Unsaturated amino-acid residues as probes for the conformation of polypeptides in solution (original) (raw)
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Journal of Controlled Release, 2000
In a new group of polypeptides, the branches were composed of DL-Ala oligopeptide, L-serine and L-leucine or L-glutamic acid residues. The synthesis of eight different side-chain combinations is described. In the first group, Ser was attached directly to the´-amino groups of polylysine, and Leu or Glu was situated at the side chain end (poly[Lys(X -DL-Alai m Ser )]). Alternatively, Leu or Glu was positioned next to the polylysine backbone (poly[Lys(Ser -DL-Ala -X )], where j j m i X5L-Leu or L-Glu and m|3-6, i#1 and j#1). The second group of polymers was synthesised by grafting oligo(DL-alanine) chains to the e-amino groups of polylysine, followed by coupling of Ser and Leu or Glu consecutively to the chain ends, however, in a different order, resulting in the polymers (poly[Lys(X -Ser -DL-Ala )] and poly[Lys(Ser -X -DL-Ala )], i j m j i m
Chirality, 2003
Circular dichroism (CD) spectra in the region of 210-250 nm allow visualization of intrachain phase transition of pH-and thermosensitive polyelectrolytes. Indeed, in 0.001 M citrate and acetate buffers, at pH 4.0-5.5, aqueous solutions of a poly(N-isopropylacrylamide-co-N-methacryloyl-L-leucine) (NIPAAm-MALEU) copolymer containing 90.9 mol% of NIPAAm residues exhibit a well-defined sigmoidal increase in the CD signal at 220 nm with increasing temperature. This phenomenon is suggestive of a highly cooperative transition which occurs at lower temperatures compared to that observed by cloud point measurements. The change in the CD signal is less sharp at higher pH, indicating varying cooperativity with pH. For pH 6.0 and higher, no such phenomena are observed. Chirality 15: 251-255, 2003.
Acetonitrile-induced conformational transitions in poly-l-lysine
International Journal of Biological Macromolecules, 1997
The effect of acetonitrile on the random coil, alpha-helix and beta-sheet conformations induced in poly-L-lysine is studied. It is found that acetonitrile at higher concentrations transforms the backbone of polylysine from a random coil to a helical conformation. Addition of acetonitrile to polylysine (pH 11.5) in the alpha-helix conformation, induces conformational changes in two stages. At concentrations below 60% v/v, acetonitrile stabilizes the helical conformation and at higher concentrations (> 70% v/v), it destabilizes the helix. beta-sheet-->alpha-helix-->random coil conformational transitions are found to occur when polylysine in the heat-induced conformation is titrated with acetonitrile. The possible mechanism(s) of action of acetonitrile in inducing these structural transitions is discussed.
Self-Assembly and Responsive Behavior of Poly(peptide)-Based Copolymers
Macromolecular Chemistry and Physics, 2018
Well-defined copolymers synthesized by combining poly(ethylene glycol) (PEG) and amino acid based building blocks are investigated with regard to their helical rigidity and self-assembly. Optical active block copolymers reported here are designed to have a pendant amino acid and polymerizable group, that is, isonitrile in order to induce helix formation and reduce the mobility of polymer chains by forming a hydrogen bond network so that a helix with reasonable rigidity can be obtained. Due to the amphiphilicity and a relatively shorter PEG as a coil, these polymers form micelles as observed under transmission electron microscopy in which copolymers PEG 108-b-PPIC 764 and PEG 108-b-PPIC 1020 appear to be evolving into nanoparticles with a size distribution of 100-200 nm. Circular dichroism spectroscopy is employed to study the nature of the helix and its rigidity. The folding and unfolding of polymer helix as a result of the ability of a selective solvent to form/disrupt hydrogen bonds with the peptide linkage is also discussed to highlight the responsive nature of the polymer.
Biopolymers, 1994
Vibrational CD (VCD) and electronic CD (ECD) spectra of some sequential Lys and Leu based oligo-arid polypeptides were studied as a function of added salt and (for ECD ) as a function of concentration in aqueous solution. For these samples, the VCD spectra can only be measured at relatively high concentrations under which the well-known salt-induced transition to a /3-sheet form can be observed for the KL based species, but only the endstate a-helical conformation is obvious for the LKKL based samples. ECD concentration dependence demonstrates that, at high concentration with no added or with added salt, LKKL based oligomers and polymers give a-helical spectra. These data provide evidence of aggregation induced secondary structure formation in an exceptionally simple peptide system. Similarly, the KL based oligomers and polymers give 0-sheet like spectra at high concentration or at high salt. These systems further provide model systems under "normal" aqueous conditions that yield VCD band shapes that correlate to the major secondary structural types of polypeptides. They are in substantial agreement with those spectra obtained on homopolypeptides and 011 proteins, confirming the relative independence of the VCD technique from side-chain and solvent effects.
Conformational Study of the Diastereomeric Pairs in Poly(lysine)−Pectate Complexes
Macromolecules, 2001
The complex formation in aqueous solution between the polyelectrolytes poly(lysine) and pectate was studied focusing on the conformational changes of the polysaccharidic moiety. The findings suggest that the pectate adopts a superhelical conformation around the R helix of the poly(L-lysine). A threshold value of the degree of polymerization of the pectate chain enabling the transition of the peptide was determined by chromatographic and circular dichroism methods. Conformational analysis results are in agreement with the experimental findings and support the superhelical topology of the polyelectrolyte poly(L-lysine)-pectate complex.
Biomacromolecules, 2009
We studied the self-assembly of peptide-based ABA and CBC triblock-copolymers (obtained by bacterial expression) containing random coiled hydrophilic central B blocks flanked with helical A or C blocks. The A and C blocks were of different compositions with respect to the fraction of lysine residues which provided a higher pH sensitivity of the copolymer solutions. The interchain interactions of the copolymers driven by external stimuli (pH and temperature) were explored in the process of macromolecular self-assembling in the thin films of the copolymer solutions deposited on the solid substrate. The interactions involved in the macromolecular association affected the morphology of the developed patterns. The polypeptide of the B block was not involved in the formation of the secondary structures, while the A and C blocks demonstrated helical folding responsible for the intermolecular association. The mechanism of the responsive behavior of the copolymers is based on the reversible assembling of the helices into coiled-coil structures upon the change of pH or temperature. It was found that at low pH values, when electrostatic repulsion was strong and the A/C blocks unfolded, assembling yielded fractal dendrites. Increasing the pH resulted in the recovery of the helical conformation of the A/C blocks and caused a transition from the fractal to compact structures. An elevation of temperature resulted in the disruption of the dendritic structures. The reported here approach to the evaluation of the intermolecular interactions, based on the analysis of the dendritic patterns, provides a rapid and simple method for the characterization of complex processes of self-assembling biomacromolecules.
Chirality and helix stability of polyglutamic acid enantiomers
Journal of Colloid and Interface Science, 2008
In this work the chirality and the relative thermal stability of ordered micellar aggregates of poly-L-and poly-D-glutamic acids with the cationic surfactant C 14 TAB is examined. The complexed mesophases poly-L-Glu/C 14 TAB and poly-D-Glu/C 14 TAB were characterized by circular dichroism (CD) in the temperature range 10-70 • C for their chirality and thermal stability as well as by X-ray diffraction (XRD) for the micellar ordered structure. Low angle XRD analysis showed that both micellar aggregates poly-L-Glu/C 14 TAB and poly-D-Glu/C 14 TAB are hexagonally packed in a MCM-41 fashion with an intermicellar distance identical and equal to 3.55 ± 0.10 nm. The CD spectra indicated that both complexes poly-L-Glu/C 14 TAB and poly-D-Glu/C 14 TAB possess a mainly α-helix structure and are exact mirror images to each other. The same mirror images and a mainly α-helix configuration were also observed by CD for the free poly-L-and poly-D-glutamic acids at room temperature. As the temperature increases from 10 up to 70 • C the α-helix of the poly-L-glutamic acid is gradually transformed to a mixture containing increased amounts of the 3 10 -helix while the α-helix structure of the poly-D-glutamic acid is constantly degenerated. In contrast the α-helices of the corresponding complexes poly-L-Glu/C 14 TAB and poly-D-Glu/C 14 TAB are degenerated upon heating without appreciable increase of the 3 10 -helices as an intermediate configuration. This difference in helix conservation is attributed to increase protection of the L-enantiomers, compared to D-enantiomers, which might be related to the survival of L-aminoacids in the living world.