Ayyalusamy Ramamoorthy | University of Michigan (original) (raw)
Papers by Ayyalusamy Ramamoorthy
The Journal of chemical physics, Jan 28, 2015
A proton-detected 3D (1)H/(13)C/(1)H chemical shift correlation experiment is proposed for the as... more A proton-detected 3D (1)H/(13)C/(1)H chemical shift correlation experiment is proposed for the assignment of chemical shift resonances, identification of (13)C-(1)H connectivities, and proximities of (13)C-(1)H and (1)H-(1)H nuclei under ultrafast magic-angle-spinning (ultrafast-MAS) conditions. Ultrafast-MAS is used to suppress all anisotropic interactions including (1)H-(1)H dipolar couplings, while the finite-pulse radio frequency driven dipolar recoupling (fp-RFDR) pulse sequence is used to recouple dipolar couplings among protons and the insensitive nuclei enhanced by polarization transfer technique is used to transfer magnetization between heteronuclear spins. The 3D experiment eliminates signals from non-carbon-bonded protons and non-proton-bonded carbons to enhance spectral resolution. The 2D (F1/F3) (1)H/(1)H and 2D (13)C/(1)H (F2/F3) chemical shift correlation spectra extracted from the 3D spectrum enable the identification of (1)H-(1)H proximity and (13)C-(1)H connectivit...
Chemical Communications, 2013
The aggregation of human islet amyloid polypeptide (hIAPP) has been linked to beta-cell death in ... more The aggregation of human islet amyloid polypeptide (hIAPP) has been linked to beta-cell death in type II diabetes. Zinc present in secretory granules has been shown to affect this aggregation. A combination of EXAFS, NMR, and AFM experiments shows that the influence of zinc is most likely due to the stabilization of prefibrillar aggregates of hIAPP.
Biophysical Journal, 2013
Chemical Communications, 2013
The aggregation of human islet amyloid polypeptide (hIAPP) has been linked to beta-cell death in ... more The aggregation of human islet amyloid polypeptide (hIAPP) has been linked to beta-cell death in type II diabetes. Zinc present in secretory granules has been shown to affect this aggregation. A combination of EXAFS, NMR, and AFM experiments shows that the influence of zinc is most likely due to the stabilization of prefibrillar aggregates of hIAPP.
Biophysical Journal, 2013
solutions of mTFP-PNA monomer units resulted in template directed induced assembly. Assembly was ... more solutions of mTFP-PNA monomer units resulted in template directed induced assembly. Assembly was confirmed by SDS-PAGE, mass spectrometry, and size exclusion HPLC. Fluorescence anisotropy was monitored over the course of a mTFP-PNA:DNA titration. Template coding for dimer formation was studied. The anisotropy showed a decreasing trend related to homo-FRET in the assembled forms. A maximal reduction (41%) was observed at a DNA to mTFP-PNA ratio of 1:2. Anisotropy, then increased steadily up to a 1:1 ratio. This study demonstrates an inducibly assembled homo-FRET system using expressed protein ligation which may be extended to study oligomerization and cluster formation in living systems.
Biophysical Journal, 2013
The Journal of chemical physics, Jan 21, 2016
Establishing connectivity and proximity of nuclei is an important step in elucidating the structu... more Establishing connectivity and proximity of nuclei is an important step in elucidating the structure and dynamics of molecules in solids using magic angle spinning (MAS) NMR spectroscopy. Although recent studies have successfully demonstrated the feasibility of proton-detected multidimensional solid-state NMR experiments under ultrafast-MAS frequencies and obtaining high-resolution spectral lines of protons, assignment of proton resonances is a major challenge. In this study, we first re-visit and demonstrate the feasibility of 2D constant-time uniform-sign cross-peak correlation (CTUC-COSY) NMR experiment on rigid solids under ultrafast-MAS conditions, where the sensitivity of the experiment is enhanced by the reduced spin-spin relaxation rate and the use of low radio-frequency power for heteronuclear decoupling during the evolution intervals of the pulse sequence. In addition, we experimentally demonstrate the performance of a proton-detected pulse sequence to obtain a 3D (1)H/(13)...
Biochimica et Biophysica Acta (BBA) - Biomembranes, 2006
A 15-residue peptide dimer G15 derived from the cell lytic protein granulysin has been shown to e... more A 15-residue peptide dimer G15 derived from the cell lytic protein granulysin has been shown to exert potent activity against microbes, including E. coli, but not against human Jurkat cells [tumoricidal activities of synthetic peptides derived from granulysin. J. Immunol. 165 (2000Immunol. 165 ( ) 1486Immunol. 165 ( -1490. We investigated the target membrane selectivity of G15 using fluorescence, circular dichroism and 31 P NMR methods. The ANS uptake assay shows that the extent of E. coli outer membrane disruption depends on G15 concentration. 31 P NMR spectra obtained from E. coli total lipid bilayers incorporated with G15 show disruption of lipid bilayers. Fluorescence binding studies on the interaction of G15 with synthetic liposomes formed of E. coli lipids suggest a tight binding of the peptide at the membrane interface. The peptide also binds to negatively charged POPC/POPG (3:1) lipid vesicles but fails to insert deep into the membrane interior. These results are supported by the peptide-induced changes in the measured isotropic chemical shift and T1 values of POPG in 3:1 POPC:POPG multilamellar vesicles while neither a non-lamellar phase nor a fragmentation of bilayers was observed from NMR studies. The circular dichroism studies reveal that the peptide exists as a random coil in solution but folds into a less ordered conformation upon binding to POPC/POPG (3:1) vesicles. However, G15 does not bind to lipid vesicles made of POPC/POPG/Chl (9:1:1) mixture, mimicking tumor cell membrane. These results explain the susceptibility of E. coli and the resistance of human Jurkat cells to G15, and may have implications in designing membrane-selective therapeutic agents.
The journal of physical chemistry. B, 2012
The hierarchical heterogeneous architecture of bone imposes significant challenges to structural ... more The hierarchical heterogeneous architecture of bone imposes significant challenges to structural and dynamic studies conducted by traditional biophysical techniques. High-resolution solid-state nuclear magnetic resonance (SSNMR) spectroscopy is capable of providing detailed atomic-level structural insights into such traditionally challenging materials. However, the relatively long data-collection time necessary to achieve a reliable signal-to-noise ratio (S/N) remains a major limitation for the widespread application of SSNMR on bone and related biomaterials. In this study, we attempt to overcome this limitation by employing the paramagnetic relaxation properties of copper(II) ions to shorten the (1)H intrinsic spin-lattice (T(1)) relaxation times measured in natural-abundance (13)C cross-polarization (CP) magic-angle-spinning (MAS) NMR experiments on bone tissues for the purpose of accelerating the data acquisition time in SSNMR. To this end, high-resolution solid-state (13)C CPMAS experiments were conducted on type I collagen (bovine tendon), bovine cortical bone, and demineralized bovine cortical bone, each in powdered form, to measure the (1)H T(1) values in the absence and in the presence of 30 mM Cu(II)(NH(4))(2)EDTA. Our results show that the (1)H T(1) values were successfully reduced by a factor of 2.2, 2.9, and 3.2 for bovine cortical bone, type I collagen, and demineralized bone, respectively, without reducing the spectral resolution and thus enabling faster data acquisition. In addition, paramagnetic quenching of particular (13)C NMR resonances on exposure to Cu(2+) ions in the absence of mineral was also observed, potentially suggesting the relative proximity of three main amino acids in the protein backbone (glycine, proline, and alanine) to the bone mineral surface.
Journal of solid state chemistry, 2013
Solid-state (magic-angle spinning) NMR spectroscopy is a useful tool for obtaining structural inf... more Solid-state (magic-angle spinning) NMR spectroscopy is a useful tool for obtaining structural information on bone organic and mineral components and synthetic model minerals at the atomic-level. Raman and (31)P NMR spectral parameters were investigated in a series of synthetic B-type carbonated apatites (CAps). Inverse (31)P NMR linewidth and inverse Raman PO4 (3-) ν1 bandwidth were both correlated with powder XRD c-axis crystallinity over the 0.3-10.3 wt% CO3 (2-) range investigated. Comparison with bone powder crystallinities showed agreement with values predicted by NMR and Raman calibration curves. Carbonate content was divided into two domains by the (31)P NMR chemical shift frequency and the Raman phosphate ν1 band position. These parameters remain stable except for an abrupt transition at 6.5 wt% carbonate, a composition which corresponds to an average of one carbonate per unit cell. This near-binary distribution of spectroscopic properties was also found in AFM-measured particle sizes and Ca/P molar ratios by elemental analysis. We propose that this transition differentiates between two charge-balancing ion-loss mechanisms as measured by Ca/P ratios. These results define a criterion for spectroscopic characterization of B-type carbonate substitution in apatitic minerals.
Metal ion homeostasis in conjunction with amyloid-b (Ab) aggregation in the brain has been implic... more Metal ion homeostasis in conjunction with amyloid-b (Ab) aggregation in the brain has been implicated in Alzheimer's disease (AD) pathogenesis. To uncover the interplay between metal ions and Ab peptides, synthetic, multifunctional small molecules have been employed to modulate Ab aggregation in vitro.
Alzheimer's disease (AD) is a complex, multifactorial, neurodegenerative disease that poses treme... more Alzheimer's disease (AD) is a complex, multifactorial, neurodegenerative disease that poses tremendous difficulties in pinpointing its precise etiology. A toolkit, which specifically targets and modulates suggested key players, may elucidate their roles in disease onset and progression.
![Research paper thumbnail of High-Resolution Characterization of Liquid-Crystalline [60]Fullerenes Using Solid-State Nuclear Magnetic Resonance Spectroscopy](https://attachments.academia-assets.com/38853831/thumbnails/1.jpg)
](Liquid-crystalline materials containing fullerenes are valuable in the development of supramolecu... more Liquid-crystalline materials containing fullerenes are valuable in the development of supramolecular switches
and in solar cell technology. In this study, we characterize the liquid-crystalline and dynamic properties of
fullerene-containing thermotropic compounds using solid-state natural abundance 13 C NMR experiments under
stationary and magic angle spinning sample conditions. Chemical shifts spectra were measured in isotropic,
liquid-crystalline nematic and smectic A and crystalline phases using one-dimensional 13 C experiments, while
two-dimensional separated local-field experiments were used to measure the 1 H- 13 C dipolar couplings in
mesophases. Chemical shift and dipolar coupling parameters were used to characterize the structure and
dynamics of the liquid-crystalline dyads. NMR data of fullerene-containing thermotropic liquid crystals are
compared to that of basic mesogenic unit and mesomorphic promoter compounds. Our NMR results suggest
that the fullerene-ferrocene dyads form highly dynamic liquid-crystalline phases in which molecules rotate
fast around the symmetry axis on the characteristic NMR time scale of ∼ 10-4 s.
Biochemistry, 2004
LL-37 is a cationic, amphipathic R-helical antimicrobial peptide found in humans that kills cells... more LL-37 is a cationic, amphipathic R-helical antimicrobial peptide found in humans that kills cells by disrupting the cell membrane. To disrupt membranes, antimicrobial peptides such as LL-37 must alter the hydrophobic core of the bilayer. Differential scanning calorimetry and deuterium ( 2 H) NMR experiments on acyl chain perdeuterated lipids demonstrate that LL-37 inserts into the hydrophobic region of the bilayer and alters the chain packing and cooperativity. The results show that hydrophobic interactions between LL-37 and the hydrophobic acyl chains are as important for the ability of this peptide to disrupt lipid bilayers as its electrostatic interactions with the polar headgroups. The 2 H NMR data are consistent with the previously determined surface orientation of LL-37 (Henzler Wildman, K. A., et al. (2003) Biochemistry 42, 6545) with an estimated 5-6 Å depth of penetration of the hydrophobic face of the amphipathic helix into the hydrophobic interior of the bilayer. LL-37 also alters the material properties of lipid bilayers, including the area per lipid, hydrophobic thickness, and coefficient of thermal expansion in a manner that varies with lipid type and temperature. Comparison of the effect of LL-37 on 1-palmitoyl-2-oleoyl-phosphatidylcholine (POPC-d 31 ) and 1,2-dimyristoyl-phosphatidylcholine (DMPC-d 54 ) at different temperatures demonstrates the importance of bilayer order in determining the type and extent of disordering and disruption of the hydrophobic core by LL-37. One possible explanation, which accounts for both the 2 H NMR data presented here and the known surface orientation of LL-37 under identical conditions, is that bilayer order influences the depth of insertion of LL-37 into the hydrophobic/hydrophilic interface of the bilayer, altering the balance of electrostatic and hydrophobic interactions between the peptide and the lipids.
The Journal of Chemical Physics, 2008
A new type of spin diffusion, cross-relaxation driven spin diffusion (CRDSD), is investigated usi... more A new type of spin diffusion, cross-relaxation driven spin diffusion (CRDSD), is investigated using (15)N NMR on a N-acetyl-L-valyl-L-leucine (NAVL) single crystal under stationary condition. A two-dimensional (2D) pulse sequence that correlates the chemical shifts of (15)N nuclei, with a radio-frequency spin lock on the (15)N channel during the mixing time, is used to observe CRDSD. Experimental results obtained using CRDSD, rf-driven spin diffusion, and proton driven spin diffusion approaches on the NAVL single crystal are compared. Our experimental results suggest that the (15)N spin diffusion rate can be enhanced by about 1000 times using CRDSD than by the normal proton driven spin diffusion. Interestingly, the required spin-locking rf field strength for CRDSD is much lower than that used for the rf-driven spin diffusion experiments. The cross-peak patterns observed in 2D (15)N-(15)N correlation spectra using CRDSD and RFDSD are very different as they arise from different spin-spin interactions. A detailed theory describing CRDSD and RFDSD processes is also presented using a thermodynamic model. The speedy spin diffusion process rendered by the CRDSD approach will be useful to assign resonances from a uniformly (15)N or (13)C labeled proteins and peptides, particularly in aligned samples.
Journal of the American Chemical Society, 2009
Understanding the structure and structural changes of bone, a highly heterogeneous material with ... more Understanding the structure and structural changes of bone, a highly heterogeneous material with a complex hierarchical architecture, continues to be a significant challenge even for high-resolution solid-state NMR spectroscopy. While it is known that dehydration affects mechanical properties of bone by decreasing its strength and toughness, the underlying structural mechanism at atomic-level is unknown. Solid-state NMR spectroscopy, controlled dehydration, and H/D exchange are used for the first time to reveal the structural changes of an intact piece of bovine cortical bone. Proton spectra are used to monitor the dehydration of bone inside the rotor and high-resolution 13 C chemical shift spectra obtained under magic angle spinning are used evaluate the dehydration-induced conformational changes in bone. Experiments reveal the slow denaturation of collagen while the trans-Xaa-Pro conformation in collagen is unchanged due to dehydration. Our results suggest that GAGs in the collagen fiber and mineral interface may chelate with a Ca 2+ ion present on the surface of the mineral through sulfate or carboxylate groups. These results provide insights into the role of water molecules in the bone structure and shed light on the relationship between the structure and mechanics of bone.
Journal of the American Chemical Society, 2009
. CD spectra of 25 µM PAP 248-286 in 10 mM Sodium Phosphate buffer with 100 mM NaF at pH 7.3 titr... more . CD spectra of 25 µM PAP 248-286 in 10 mM Sodium Phosphate buffer with 100 mM NaF at pH 7.3 titrated with a 10 mM SDS stock solution (A) or trifluorethanol (TFE) (B). Reference 6 in the main text: Munch, J.; Rucker, E.; Standker, L.; Adermann, K.; Goffinet, C.; Schindler, M.; Wildum, S.; Chinnadurai, R.; Rajan, D.; Specht, A.; Gimenez-Gallego, G.; Sanchez, P. C.; Fowler, D. M.; Koulov, A.; Kelly, J. W.; Mothes, W.; Grivel, J. C.; Margolis, L.; Keppler, O. T.; Forssmann, W. G.; Kirchhoff, F. Cell 2007, 131, 1059-1071.
Journal of Proteome Research, 2011
High-resolution magic-angle spinning (HR-MAS) proton NMR spectroscopy is used to explore the meta... more High-resolution magic-angle spinning (HR-MAS) proton NMR spectroscopy is used to explore the metabolic signatures of head and neck squamous cell carcinoma (HNSCC) which included matched normal adjacent tissue (NAT) and tumor originating from tongue, lip, larynx and oral cavity, and associated lymph-node metastatic (LN-Met) tissues. A total of 43 tissues (18 NAT, 18 Tumor and 7 LN-Met) from twenty-two HNSCC patients were analyzed. Principal Component Analysis of NMR data showed a clear classification between NAT and tumor tissues, however, LN-Met tissues were classified among tumor. A partial least squares discriminant analysis model generated from NMR metabolic profiles was used to differentiate normal from tumor samples (Q 2 > 0.80, Receiver Operator Characteristic area under the curve > 0. 86, using 7-fold cross validation). HNSCC and LN-Met tissues showed elevated levels of lactate, amino acids including leucine, isoleucine, valine, alanine, glutamine, glutamate, aspartate, glycine, phenylalanine and tyrosine, choline containing compounds, creatine, taurine, glutathione and decreased levels of triglycerides. These elevated metabolites were associated with highly active glycolysis, increased amino acids influx (anaplerosis) into the TCA cycle, altered energy metabolism, membrane choline phospholipid metabolism, and oxidative and osmotic defense mechanisms. Moreover, decreased levels of triglycerides may indicate lipolysis followed by β-oxidation of fatty acids that may exist to deliver bioenergy for rapid tumor cell proliferation and growth.
The Journal of chemical physics, Jan 28, 2015
A proton-detected 3D (1)H/(13)C/(1)H chemical shift correlation experiment is proposed for the as... more A proton-detected 3D (1)H/(13)C/(1)H chemical shift correlation experiment is proposed for the assignment of chemical shift resonances, identification of (13)C-(1)H connectivities, and proximities of (13)C-(1)H and (1)H-(1)H nuclei under ultrafast magic-angle-spinning (ultrafast-MAS) conditions. Ultrafast-MAS is used to suppress all anisotropic interactions including (1)H-(1)H dipolar couplings, while the finite-pulse radio frequency driven dipolar recoupling (fp-RFDR) pulse sequence is used to recouple dipolar couplings among protons and the insensitive nuclei enhanced by polarization transfer technique is used to transfer magnetization between heteronuclear spins. The 3D experiment eliminates signals from non-carbon-bonded protons and non-proton-bonded carbons to enhance spectral resolution. The 2D (F1/F3) (1)H/(1)H and 2D (13)C/(1)H (F2/F3) chemical shift correlation spectra extracted from the 3D spectrum enable the identification of (1)H-(1)H proximity and (13)C-(1)H connectivit...
Chemical Communications, 2013
The aggregation of human islet amyloid polypeptide (hIAPP) has been linked to beta-cell death in ... more The aggregation of human islet amyloid polypeptide (hIAPP) has been linked to beta-cell death in type II diabetes. Zinc present in secretory granules has been shown to affect this aggregation. A combination of EXAFS, NMR, and AFM experiments shows that the influence of zinc is most likely due to the stabilization of prefibrillar aggregates of hIAPP.
Biophysical Journal, 2013
Chemical Communications, 2013
The aggregation of human islet amyloid polypeptide (hIAPP) has been linked to beta-cell death in ... more The aggregation of human islet amyloid polypeptide (hIAPP) has been linked to beta-cell death in type II diabetes. Zinc present in secretory granules has been shown to affect this aggregation. A combination of EXAFS, NMR, and AFM experiments shows that the influence of zinc is most likely due to the stabilization of prefibrillar aggregates of hIAPP.
Biophysical Journal, 2013
solutions of mTFP-PNA monomer units resulted in template directed induced assembly. Assembly was ... more solutions of mTFP-PNA monomer units resulted in template directed induced assembly. Assembly was confirmed by SDS-PAGE, mass spectrometry, and size exclusion HPLC. Fluorescence anisotropy was monitored over the course of a mTFP-PNA:DNA titration. Template coding for dimer formation was studied. The anisotropy showed a decreasing trend related to homo-FRET in the assembled forms. A maximal reduction (41%) was observed at a DNA to mTFP-PNA ratio of 1:2. Anisotropy, then increased steadily up to a 1:1 ratio. This study demonstrates an inducibly assembled homo-FRET system using expressed protein ligation which may be extended to study oligomerization and cluster formation in living systems.
Biophysical Journal, 2013
The Journal of chemical physics, Jan 21, 2016
Establishing connectivity and proximity of nuclei is an important step in elucidating the structu... more Establishing connectivity and proximity of nuclei is an important step in elucidating the structure and dynamics of molecules in solids using magic angle spinning (MAS) NMR spectroscopy. Although recent studies have successfully demonstrated the feasibility of proton-detected multidimensional solid-state NMR experiments under ultrafast-MAS frequencies and obtaining high-resolution spectral lines of protons, assignment of proton resonances is a major challenge. In this study, we first re-visit and demonstrate the feasibility of 2D constant-time uniform-sign cross-peak correlation (CTUC-COSY) NMR experiment on rigid solids under ultrafast-MAS conditions, where the sensitivity of the experiment is enhanced by the reduced spin-spin relaxation rate and the use of low radio-frequency power for heteronuclear decoupling during the evolution intervals of the pulse sequence. In addition, we experimentally demonstrate the performance of a proton-detected pulse sequence to obtain a 3D (1)H/(13)...
Biochimica et Biophysica Acta (BBA) - Biomembranes, 2006
A 15-residue peptide dimer G15 derived from the cell lytic protein granulysin has been shown to e... more A 15-residue peptide dimer G15 derived from the cell lytic protein granulysin has been shown to exert potent activity against microbes, including E. coli, but not against human Jurkat cells [tumoricidal activities of synthetic peptides derived from granulysin. J. Immunol. 165 (2000Immunol. 165 ( ) 1486Immunol. 165 ( -1490. We investigated the target membrane selectivity of G15 using fluorescence, circular dichroism and 31 P NMR methods. The ANS uptake assay shows that the extent of E. coli outer membrane disruption depends on G15 concentration. 31 P NMR spectra obtained from E. coli total lipid bilayers incorporated with G15 show disruption of lipid bilayers. Fluorescence binding studies on the interaction of G15 with synthetic liposomes formed of E. coli lipids suggest a tight binding of the peptide at the membrane interface. The peptide also binds to negatively charged POPC/POPG (3:1) lipid vesicles but fails to insert deep into the membrane interior. These results are supported by the peptide-induced changes in the measured isotropic chemical shift and T1 values of POPG in 3:1 POPC:POPG multilamellar vesicles while neither a non-lamellar phase nor a fragmentation of bilayers was observed from NMR studies. The circular dichroism studies reveal that the peptide exists as a random coil in solution but folds into a less ordered conformation upon binding to POPC/POPG (3:1) vesicles. However, G15 does not bind to lipid vesicles made of POPC/POPG/Chl (9:1:1) mixture, mimicking tumor cell membrane. These results explain the susceptibility of E. coli and the resistance of human Jurkat cells to G15, and may have implications in designing membrane-selective therapeutic agents.
The journal of physical chemistry. B, 2012
The hierarchical heterogeneous architecture of bone imposes significant challenges to structural ... more The hierarchical heterogeneous architecture of bone imposes significant challenges to structural and dynamic studies conducted by traditional biophysical techniques. High-resolution solid-state nuclear magnetic resonance (SSNMR) spectroscopy is capable of providing detailed atomic-level structural insights into such traditionally challenging materials. However, the relatively long data-collection time necessary to achieve a reliable signal-to-noise ratio (S/N) remains a major limitation for the widespread application of SSNMR on bone and related biomaterials. In this study, we attempt to overcome this limitation by employing the paramagnetic relaxation properties of copper(II) ions to shorten the (1)H intrinsic spin-lattice (T(1)) relaxation times measured in natural-abundance (13)C cross-polarization (CP) magic-angle-spinning (MAS) NMR experiments on bone tissues for the purpose of accelerating the data acquisition time in SSNMR. To this end, high-resolution solid-state (13)C CPMAS experiments were conducted on type I collagen (bovine tendon), bovine cortical bone, and demineralized bovine cortical bone, each in powdered form, to measure the (1)H T(1) values in the absence and in the presence of 30 mM Cu(II)(NH(4))(2)EDTA. Our results show that the (1)H T(1) values were successfully reduced by a factor of 2.2, 2.9, and 3.2 for bovine cortical bone, type I collagen, and demineralized bone, respectively, without reducing the spectral resolution and thus enabling faster data acquisition. In addition, paramagnetic quenching of particular (13)C NMR resonances on exposure to Cu(2+) ions in the absence of mineral was also observed, potentially suggesting the relative proximity of three main amino acids in the protein backbone (glycine, proline, and alanine) to the bone mineral surface.
Journal of solid state chemistry, 2013
Solid-state (magic-angle spinning) NMR spectroscopy is a useful tool for obtaining structural inf... more Solid-state (magic-angle spinning) NMR spectroscopy is a useful tool for obtaining structural information on bone organic and mineral components and synthetic model minerals at the atomic-level. Raman and (31)P NMR spectral parameters were investigated in a series of synthetic B-type carbonated apatites (CAps). Inverse (31)P NMR linewidth and inverse Raman PO4 (3-) ν1 bandwidth were both correlated with powder XRD c-axis crystallinity over the 0.3-10.3 wt% CO3 (2-) range investigated. Comparison with bone powder crystallinities showed agreement with values predicted by NMR and Raman calibration curves. Carbonate content was divided into two domains by the (31)P NMR chemical shift frequency and the Raman phosphate ν1 band position. These parameters remain stable except for an abrupt transition at 6.5 wt% carbonate, a composition which corresponds to an average of one carbonate per unit cell. This near-binary distribution of spectroscopic properties was also found in AFM-measured particle sizes and Ca/P molar ratios by elemental analysis. We propose that this transition differentiates between two charge-balancing ion-loss mechanisms as measured by Ca/P ratios. These results define a criterion for spectroscopic characterization of B-type carbonate substitution in apatitic minerals.
Metal ion homeostasis in conjunction with amyloid-b (Ab) aggregation in the brain has been implic... more Metal ion homeostasis in conjunction with amyloid-b (Ab) aggregation in the brain has been implicated in Alzheimer's disease (AD) pathogenesis. To uncover the interplay between metal ions and Ab peptides, synthetic, multifunctional small molecules have been employed to modulate Ab aggregation in vitro.
Alzheimer's disease (AD) is a complex, multifactorial, neurodegenerative disease that poses treme... more Alzheimer's disease (AD) is a complex, multifactorial, neurodegenerative disease that poses tremendous difficulties in pinpointing its precise etiology. A toolkit, which specifically targets and modulates suggested key players, may elucidate their roles in disease onset and progression.
Liquid-crystalline materials containing fullerenes are valuable in the development of supramolecu... more Liquid-crystalline materials containing fullerenes are valuable in the development of supramolecular switches
and in solar cell technology. In this study, we characterize the liquid-crystalline and dynamic properties of
fullerene-containing thermotropic compounds using solid-state natural abundance 13 C NMR experiments under
stationary and magic angle spinning sample conditions. Chemical shifts spectra were measured in isotropic,
liquid-crystalline nematic and smectic A and crystalline phases using one-dimensional 13 C experiments, while
two-dimensional separated local-field experiments were used to measure the 1 H- 13 C dipolar couplings in
mesophases. Chemical shift and dipolar coupling parameters were used to characterize the structure and
dynamics of the liquid-crystalline dyads. NMR data of fullerene-containing thermotropic liquid crystals are
compared to that of basic mesogenic unit and mesomorphic promoter compounds. Our NMR results suggest
that the fullerene-ferrocene dyads form highly dynamic liquid-crystalline phases in which molecules rotate
fast around the symmetry axis on the characteristic NMR time scale of ∼ 10-4 s.
Biochemistry, 2004
LL-37 is a cationic, amphipathic R-helical antimicrobial peptide found in humans that kills cells... more LL-37 is a cationic, amphipathic R-helical antimicrobial peptide found in humans that kills cells by disrupting the cell membrane. To disrupt membranes, antimicrobial peptides such as LL-37 must alter the hydrophobic core of the bilayer. Differential scanning calorimetry and deuterium ( 2 H) NMR experiments on acyl chain perdeuterated lipids demonstrate that LL-37 inserts into the hydrophobic region of the bilayer and alters the chain packing and cooperativity. The results show that hydrophobic interactions between LL-37 and the hydrophobic acyl chains are as important for the ability of this peptide to disrupt lipid bilayers as its electrostatic interactions with the polar headgroups. The 2 H NMR data are consistent with the previously determined surface orientation of LL-37 (Henzler Wildman, K. A., et al. (2003) Biochemistry 42, 6545) with an estimated 5-6 Å depth of penetration of the hydrophobic face of the amphipathic helix into the hydrophobic interior of the bilayer. LL-37 also alters the material properties of lipid bilayers, including the area per lipid, hydrophobic thickness, and coefficient of thermal expansion in a manner that varies with lipid type and temperature. Comparison of the effect of LL-37 on 1-palmitoyl-2-oleoyl-phosphatidylcholine (POPC-d 31 ) and 1,2-dimyristoyl-phosphatidylcholine (DMPC-d 54 ) at different temperatures demonstrates the importance of bilayer order in determining the type and extent of disordering and disruption of the hydrophobic core by LL-37. One possible explanation, which accounts for both the 2 H NMR data presented here and the known surface orientation of LL-37 under identical conditions, is that bilayer order influences the depth of insertion of LL-37 into the hydrophobic/hydrophilic interface of the bilayer, altering the balance of electrostatic and hydrophobic interactions between the peptide and the lipids.
The Journal of Chemical Physics, 2008
A new type of spin diffusion, cross-relaxation driven spin diffusion (CRDSD), is investigated usi... more A new type of spin diffusion, cross-relaxation driven spin diffusion (CRDSD), is investigated using (15)N NMR on a N-acetyl-L-valyl-L-leucine (NAVL) single crystal under stationary condition. A two-dimensional (2D) pulse sequence that correlates the chemical shifts of (15)N nuclei, with a radio-frequency spin lock on the (15)N channel during the mixing time, is used to observe CRDSD. Experimental results obtained using CRDSD, rf-driven spin diffusion, and proton driven spin diffusion approaches on the NAVL single crystal are compared. Our experimental results suggest that the (15)N spin diffusion rate can be enhanced by about 1000 times using CRDSD than by the normal proton driven spin diffusion. Interestingly, the required spin-locking rf field strength for CRDSD is much lower than that used for the rf-driven spin diffusion experiments. The cross-peak patterns observed in 2D (15)N-(15)N correlation spectra using CRDSD and RFDSD are very different as they arise from different spin-spin interactions. A detailed theory describing CRDSD and RFDSD processes is also presented using a thermodynamic model. The speedy spin diffusion process rendered by the CRDSD approach will be useful to assign resonances from a uniformly (15)N or (13)C labeled proteins and peptides, particularly in aligned samples.
Journal of the American Chemical Society, 2009
Understanding the structure and structural changes of bone, a highly heterogeneous material with ... more Understanding the structure and structural changes of bone, a highly heterogeneous material with a complex hierarchical architecture, continues to be a significant challenge even for high-resolution solid-state NMR spectroscopy. While it is known that dehydration affects mechanical properties of bone by decreasing its strength and toughness, the underlying structural mechanism at atomic-level is unknown. Solid-state NMR spectroscopy, controlled dehydration, and H/D exchange are used for the first time to reveal the structural changes of an intact piece of bovine cortical bone. Proton spectra are used to monitor the dehydration of bone inside the rotor and high-resolution 13 C chemical shift spectra obtained under magic angle spinning are used evaluate the dehydration-induced conformational changes in bone. Experiments reveal the slow denaturation of collagen while the trans-Xaa-Pro conformation in collagen is unchanged due to dehydration. Our results suggest that GAGs in the collagen fiber and mineral interface may chelate with a Ca 2+ ion present on the surface of the mineral through sulfate or carboxylate groups. These results provide insights into the role of water molecules in the bone structure and shed light on the relationship between the structure and mechanics of bone.
Journal of the American Chemical Society, 2009
. CD spectra of 25 µM PAP 248-286 in 10 mM Sodium Phosphate buffer with 100 mM NaF at pH 7.3 titr... more . CD spectra of 25 µM PAP 248-286 in 10 mM Sodium Phosphate buffer with 100 mM NaF at pH 7.3 titrated with a 10 mM SDS stock solution (A) or trifluorethanol (TFE) (B). Reference 6 in the main text: Munch, J.; Rucker, E.; Standker, L.; Adermann, K.; Goffinet, C.; Schindler, M.; Wildum, S.; Chinnadurai, R.; Rajan, D.; Specht, A.; Gimenez-Gallego, G.; Sanchez, P. C.; Fowler, D. M.; Koulov, A.; Kelly, J. W.; Mothes, W.; Grivel, J. C.; Margolis, L.; Keppler, O. T.; Forssmann, W. G.; Kirchhoff, F. Cell 2007, 131, 1059-1071.
Journal of Proteome Research, 2011
High-resolution magic-angle spinning (HR-MAS) proton NMR spectroscopy is used to explore the meta... more High-resolution magic-angle spinning (HR-MAS) proton NMR spectroscopy is used to explore the metabolic signatures of head and neck squamous cell carcinoma (HNSCC) which included matched normal adjacent tissue (NAT) and tumor originating from tongue, lip, larynx and oral cavity, and associated lymph-node metastatic (LN-Met) tissues. A total of 43 tissues (18 NAT, 18 Tumor and 7 LN-Met) from twenty-two HNSCC patients were analyzed. Principal Component Analysis of NMR data showed a clear classification between NAT and tumor tissues, however, LN-Met tissues were classified among tumor. A partial least squares discriminant analysis model generated from NMR metabolic profiles was used to differentiate normal from tumor samples (Q 2 > 0.80, Receiver Operator Characteristic area under the curve > 0. 86, using 7-fold cross validation). HNSCC and LN-Met tissues showed elevated levels of lactate, amino acids including leucine, isoleucine, valine, alanine, glutamine, glutamate, aspartate, glycine, phenylalanine and tyrosine, choline containing compounds, creatine, taurine, glutathione and decreased levels of triglycerides. These elevated metabolites were associated with highly active glycolysis, increased amino acids influx (anaplerosis) into the TCA cycle, altered energy metabolism, membrane choline phospholipid metabolism, and oxidative and osmotic defense mechanisms. Moreover, decreased levels of triglycerides may indicate lipolysis followed by β-oxidation of fatty acids that may exist to deliver bioenergy for rapid tumor cell proliferation and growth.