Sunney Chan - Academia.edu (original) (raw)
Papers by Sunney Chan
Annals of the New York Academy of Sciences, 1973
ABSTRACT
Journal of Inorganic Biochemistry, 2019
Highlights Subunit B (PmoB) of particulate methane monooxygenase (pMMO) is expressed in E. coli... more Highlights Subunit B (PmoB) of particulate methane monooxygenase (pMMO) is expressed in E. coli. PmoB and its variants/mutants are expressed in the membranes as Cu I proteins. The PmoB of pMMO contains a Cu I sponge with high reduction potentials for the Cu sites. The PmoB proteins show evidence of a dinuclear copper site. The PmoB-enriched E. coli membranes produce H 2 O 2 .
Catalysis Science & Technology, 2016
Selective catalytic oxidation of hydrocarbons by a tricopper complex is demonstrated.
Journal of Inorganic Biochemistry, 2008
Earlier work from our laboratory has indicated that a hemerythrin-like protein was over-produced ... more Earlier work from our laboratory has indicated that a hemerythrin-like protein was over-produced together with the particulate methane monooxygenase (pMMO) when Methylococcus capsulatus (Bath) was grown under high copper concentrations. A homologue of hemerythrin had not previously been found in any prokaryote. To confirm its identity as a hemerythrin, we have isolated and purified this protein by ion-exchange, gel-filtration and
Proceedings of the National Academy of Sciences, 2001
We report here studies of tryptophan (Trp) solvation dynamics in water and in the Pyrococcus furi... more We report here studies of tryptophan (Trp) solvation dynamics in water and in the Pyrococcus furiosus rubredoxin protein, including the native and its apo and denatured forms. We also report results on energy transfer from Trp to the iron-sulfur [Fe-S] cluster. Trp fluorescence decay with the onset of solvation dynamics of the chromophore in water was observed with femtosecond resolution (≈160 fs; 65% component), but the emission extended to the picosecond range (1.1 ps; 35% component). In contrast, the decay is much slower in the native rubredoxin; the Trp fluorescence decay extends to 10 ps and longer, reflecting the local rigidity imposed by residues and by the surface water layer. The dynamics of resonance energy transfer from the two Trps to the [Fe-S] cluster in the protein was observed to follow a temporal behavior characterized by a single exponential (15–20 ps) decay. This unusual observation in a protein indicates that the resonance transfer is to an acceptor of a well-def...
Proceedings of the National Academy of Sciences, 2004
Whether turns play an active or passive role in protein folding remains a controversial issue at ... more Whether turns play an active or passive role in protein folding remains a controversial issue at this juncture. Here we use a photolabile cage strategy in combination with laser-flash photolysis and photoacoustic calorimetry to study the effects of different turns on the kinetics of β-hairpin refolding on a nanosecond time scale. This strategy opens up a temporal window to allow the observation of early kinetic events in the protein refolding process at ambient temperature and pH without interference from any denaturants. Our results provide direct evidence demonstrating that even a one-residue difference in the turn region can change the refolding kinetics of a peptide. This observation suggests an active role for turn formation in directing protein folding.
Journal of Bacteriology, 2003
In order to obtain particulate methane monooxygenase (pMMO)-enriched membranes from Methylococcus... more In order to obtain particulate methane monooxygenase (pMMO)-enriched membranes from Methylococcus capsulatus (Bath) with high activity and in high yields, we devised a method to process cell growth in a fermentor adapted with a hollow-fiber bioreactor that allows easy control and quantitative adjustment of the copper ion concentration in NMS medium over the time course of cell culture. This technical improvement in the method for culturing bacterial cells allowed us to study the effects of copper ion concentration in the growth medium on the copper content in the membranes, as well as the specific activity of the enzyme. The optimal copper concentration in the growth medium was found to be 30 to 35 μM. Under these conditions, the pMMO is highly expressed, accounting for 80% of the total cytoplasmic membrane proteins and having a specific activity as high as 88.9 nmol of propylene oxide/min/mg of protein with NADH as the reductant. The copper stoichiometry is ∼13 atoms per pMMO molec...
FEBS Letters, 1981
I. Introduction 11. General Considerations A. Function of the Enzyme B. Occurrence and Purificati... more I. Introduction 11. General Considerations A. Function of the Enzyme B. Occurrence and Purification of Succinyl CoA Synthetase C. Substrate Specificity 1. Succinate 2. Nucleoside Triphosphate and Diphosphate 3. Coenzyme A 4. Inorganic Phosphate 5. Divalent Metal Ion D. Michaelis Constants of Substrates Mechanism of the Succinyl CoA Synthetase Reaction A. The Phosphorylated Enzyme B. High Energy Nonphosphorylated Form of the Enzyme. Evidence C. Evidence for Intermediary Formation of Enzyme-Bound Succinyl Structural Studies of the Enzyme V. Conclusion Acknowledgement References 111. for I t s Noninvolvement in the Net Catalytic Reaction Phosphate IV. 183 184 185 185 185 * Succinate: CoA ligase (ADP), E C 6.2.1.5 and (GDP), EC 6.2.1.4, also known as the succinate-phosphorylating enzyme, P-enzyme, and succinic thiokinase.
Biophysical Journal, 2012
In recent years, various folding zones within the ribosome tunnel have been identified and explor... more In recent years, various folding zones within the ribosome tunnel have been identified and explored through x-ray, cryo-electron microscopy (cryo-EM), and molecular biology studies. Here, we generated ribosome-bound nascent polypeptide complexes (RNCs) with different polyalanine (poly-A) inserts or signal peptides from membrane/secretory proteins to explore the influence of nascent chain compaction in the Escherichia coli ribosome tunnel on chaperone recruitment. By employing timeresolved fluorescence resonance energy transfer and immunoblotting, we were able to show that the poly-A inserts embedded in the passage tunnel can form a compacted structure (presumably helix) and reduce the recruitment of Trigger Factor (TF) when the helical motif is located in the region near the tunnel exit. Similar experiments on nascent chains containing signal sequences that may form compacted structural motifs within the ribosome tunnel and lure the signal recognition particle (SRP) to the ribosome, provided additional evidence that short, compacted nascent chains interfere with TF binding. These findings shed light on the possible controlling mechanism of nascent chains within the tunnel that leads to chaperone recruitment, as well as the function of L23, the ribosomal protein that serves as docking sites for both TF and SRP, in cotranslational protein targeting.
Biochimica et Biophysica Acta (BBA) - Proteins and Proteomics, 2015
JBIC Journal of Biological Inorganic Chemistry, 2006
Pyochelin, its analog 3&a... more Pyochelin, its analog 3''-nor-NH-pyochelin, and the related methyl hydroxamate, 2-(2'-hydroxyphenyl)-4,5-dihydrothiazol-4-carboxylic acid methoxymethyl amide, have been prepared together with their Fe(III) complexes. The solution stoichiometry and the coordination of the three Fe(III) complexes in methanol or buffered (pH approximately 2) 50:50 (v/v) methanol-water mixtures were determined using various spectroscopic methods: UV-vis absorption, X-ray absorption, extended X-ray absorption fine structure and electron paramagnetic resonance. All three systems showed both a 1:1 and 2:1 ligand-Fe(III) stoichiometry, but presented different coordination properties. Conditional formation constants (pH approximately 2) were determined for both the 1:1 and 2:1 complexes in all three systems. Computation of the coordination-conformational energies by semiempirical methods indicated that the coordination in the case of the 2:1 complexes of pyochelin-Fe(III) and 3''-nor-NH-pyochelin-Fe(III) was asymmetrical, with one molecule of pyochelin (or 3''-nor-NH-pyochelin) tetradentately coordinated (O1, N1, N2 and O3) to the Fe(III), and the second molecule bound bidentately (O1, N1 or N2, O3), to complete the octahedral geometry. In contrast, two molecules of the methyl hydroxamate each provided a set of tridentate ligand atoms in the formation of the 2:1 ligand-Fe(III) complex. These results are consistent with the role of pyochelin in the uptake of iron by the FptA receptor in the outer membrane of Pseudomonas aeruginosa and in several gram-negative bacteria.
Biochemical and Biophysical Research Communications, 2008
Leishmaniasis is a tropical disease caused by Leishmania, eukaryotic parasites transmitted to hum... more Leishmaniasis is a tropical disease caused by Leishmania, eukaryotic parasites transmitted to humans by sand flies. Towards the development of new chemotherapeutic targets for this disease, biochemical and in vivo expression studies were performed on one of two M32 carboxypeptidases present within the Leishmania major (LmaCP1) genome. Enzymatic studies reveal that like previously studied M32 carboxypeptidases, LmaCP1 cleaves substrates with a variety of C-terminal amino acids-the primary exception being those having C-terminal acidic residues. Cleavage assays with a series of FRETbased peptides suggest that LmaCP1 exhibits a substrate length restriction, preferring peptides shorter than 9-12 amino acids. The in vivo expression of LmaCP1 was analyzed for each major stage of the L. major life cycle. These studies reveal that LmaCP1 expression occurs only in procyclic promastigotes-the stage of life where the organism resides in the abdominal midgut of the insect. The implications of these results are discussed.
Energy Environ. Sci.
The development of a heterogeneous catalyst capable for efficient selective conversion of methane... more The development of a heterogeneous catalyst capable for efficient selective conversion of methane into methanol with multiple turnovers under ambient conditions is reported here.
Biochemistry, 1990
The electrons enter the protein from the cytosol side of the mitochondrial inner membrane, and th... more The electrons enter the protein from the cytosol side of the mitochondrial inner membrane, and the protons consumed in the dioxygen reduction reaction are taken up from the matrix. In this manner, the sidedness of the membrane is exploited to convert redox free energy into a ...
Proceedings of the National Academy of Sciences, Apr 1, 1970
The nature of the intramolecular hydrogen bond in the enol tautomer of 2, 4-pentanedione has been... more The nature of the intramolecular hydrogen bond in the enol tautomer of 2, 4-pentanedione has been investigated by high resolution proton and deuteron magnetic resonance spectroscopy. An unusually large deuterium isotope effect on the chemical shift of the bridge hydrogen has been observed. This unexpected result, together with the observation of a pronounced temperature dependence for both the proton and deuteron resonances, suggests that two states with different chemical shifts for the bridge hydrogen ...
Biochemistry, Apr 20, 2004
The particulate methane monooxygenase (pMMO) is a complex membrane protein complex that has been ... more The particulate methane monooxygenase (pMMO) is a complex membrane protein complex that has been difficult to isolate and purify for biochemical and biophysical characterization because of its instability in detergents used to solubilize the enzyme. In this perspective, we summarize the progress recently made toward obtaining a purified pMMO-detergent complex and characterizing the enzyme in pMMO-enriched membranes. The purified pMMO is a multi-copper protein, with ca. 15 copper ions sequestered into five trinuclear copper ...
Angewandte Chemie International Edition
Annals of the New York Academy of Sciences, 1973
ABSTRACT
Journal of Inorganic Biochemistry, 2019
Highlights Subunit B (PmoB) of particulate methane monooxygenase (pMMO) is expressed in E. coli... more Highlights Subunit B (PmoB) of particulate methane monooxygenase (pMMO) is expressed in E. coli. PmoB and its variants/mutants are expressed in the membranes as Cu I proteins. The PmoB of pMMO contains a Cu I sponge with high reduction potentials for the Cu sites. The PmoB proteins show evidence of a dinuclear copper site. The PmoB-enriched E. coli membranes produce H 2 O 2 .
Catalysis Science & Technology, 2016
Selective catalytic oxidation of hydrocarbons by a tricopper complex is demonstrated.
Journal of Inorganic Biochemistry, 2008
Earlier work from our laboratory has indicated that a hemerythrin-like protein was over-produced ... more Earlier work from our laboratory has indicated that a hemerythrin-like protein was over-produced together with the particulate methane monooxygenase (pMMO) when Methylococcus capsulatus (Bath) was grown under high copper concentrations. A homologue of hemerythrin had not previously been found in any prokaryote. To confirm its identity as a hemerythrin, we have isolated and purified this protein by ion-exchange, gel-filtration and
Proceedings of the National Academy of Sciences, 2001
We report here studies of tryptophan (Trp) solvation dynamics in water and in the Pyrococcus furi... more We report here studies of tryptophan (Trp) solvation dynamics in water and in the Pyrococcus furiosus rubredoxin protein, including the native and its apo and denatured forms. We also report results on energy transfer from Trp to the iron-sulfur [Fe-S] cluster. Trp fluorescence decay with the onset of solvation dynamics of the chromophore in water was observed with femtosecond resolution (≈160 fs; 65% component), but the emission extended to the picosecond range (1.1 ps; 35% component). In contrast, the decay is much slower in the native rubredoxin; the Trp fluorescence decay extends to 10 ps and longer, reflecting the local rigidity imposed by residues and by the surface water layer. The dynamics of resonance energy transfer from the two Trps to the [Fe-S] cluster in the protein was observed to follow a temporal behavior characterized by a single exponential (15–20 ps) decay. This unusual observation in a protein indicates that the resonance transfer is to an acceptor of a well-def...
Proceedings of the National Academy of Sciences, 2004
Whether turns play an active or passive role in protein folding remains a controversial issue at ... more Whether turns play an active or passive role in protein folding remains a controversial issue at this juncture. Here we use a photolabile cage strategy in combination with laser-flash photolysis and photoacoustic calorimetry to study the effects of different turns on the kinetics of β-hairpin refolding on a nanosecond time scale. This strategy opens up a temporal window to allow the observation of early kinetic events in the protein refolding process at ambient temperature and pH without interference from any denaturants. Our results provide direct evidence demonstrating that even a one-residue difference in the turn region can change the refolding kinetics of a peptide. This observation suggests an active role for turn formation in directing protein folding.
Journal of Bacteriology, 2003
In order to obtain particulate methane monooxygenase (pMMO)-enriched membranes from Methylococcus... more In order to obtain particulate methane monooxygenase (pMMO)-enriched membranes from Methylococcus capsulatus (Bath) with high activity and in high yields, we devised a method to process cell growth in a fermentor adapted with a hollow-fiber bioreactor that allows easy control and quantitative adjustment of the copper ion concentration in NMS medium over the time course of cell culture. This technical improvement in the method for culturing bacterial cells allowed us to study the effects of copper ion concentration in the growth medium on the copper content in the membranes, as well as the specific activity of the enzyme. The optimal copper concentration in the growth medium was found to be 30 to 35 μM. Under these conditions, the pMMO is highly expressed, accounting for 80% of the total cytoplasmic membrane proteins and having a specific activity as high as 88.9 nmol of propylene oxide/min/mg of protein with NADH as the reductant. The copper stoichiometry is ∼13 atoms per pMMO molec...
FEBS Letters, 1981
I. Introduction 11. General Considerations A. Function of the Enzyme B. Occurrence and Purificati... more I. Introduction 11. General Considerations A. Function of the Enzyme B. Occurrence and Purification of Succinyl CoA Synthetase C. Substrate Specificity 1. Succinate 2. Nucleoside Triphosphate and Diphosphate 3. Coenzyme A 4. Inorganic Phosphate 5. Divalent Metal Ion D. Michaelis Constants of Substrates Mechanism of the Succinyl CoA Synthetase Reaction A. The Phosphorylated Enzyme B. High Energy Nonphosphorylated Form of the Enzyme. Evidence C. Evidence for Intermediary Formation of Enzyme-Bound Succinyl Structural Studies of the Enzyme V. Conclusion Acknowledgement References 111. for I t s Noninvolvement in the Net Catalytic Reaction Phosphate IV. 183 184 185 185 185 * Succinate: CoA ligase (ADP), E C 6.2.1.5 and (GDP), EC 6.2.1.4, also known as the succinate-phosphorylating enzyme, P-enzyme, and succinic thiokinase.
Biophysical Journal, 2012
In recent years, various folding zones within the ribosome tunnel have been identified and explor... more In recent years, various folding zones within the ribosome tunnel have been identified and explored through x-ray, cryo-electron microscopy (cryo-EM), and molecular biology studies. Here, we generated ribosome-bound nascent polypeptide complexes (RNCs) with different polyalanine (poly-A) inserts or signal peptides from membrane/secretory proteins to explore the influence of nascent chain compaction in the Escherichia coli ribosome tunnel on chaperone recruitment. By employing timeresolved fluorescence resonance energy transfer and immunoblotting, we were able to show that the poly-A inserts embedded in the passage tunnel can form a compacted structure (presumably helix) and reduce the recruitment of Trigger Factor (TF) when the helical motif is located in the region near the tunnel exit. Similar experiments on nascent chains containing signal sequences that may form compacted structural motifs within the ribosome tunnel and lure the signal recognition particle (SRP) to the ribosome, provided additional evidence that short, compacted nascent chains interfere with TF binding. These findings shed light on the possible controlling mechanism of nascent chains within the tunnel that leads to chaperone recruitment, as well as the function of L23, the ribosomal protein that serves as docking sites for both TF and SRP, in cotranslational protein targeting.
Biochimica et Biophysica Acta (BBA) - Proteins and Proteomics, 2015
JBIC Journal of Biological Inorganic Chemistry, 2006
Pyochelin, its analog 3&a... more Pyochelin, its analog 3''-nor-NH-pyochelin, and the related methyl hydroxamate, 2-(2'-hydroxyphenyl)-4,5-dihydrothiazol-4-carboxylic acid methoxymethyl amide, have been prepared together with their Fe(III) complexes. The solution stoichiometry and the coordination of the three Fe(III) complexes in methanol or buffered (pH approximately 2) 50:50 (v/v) methanol-water mixtures were determined using various spectroscopic methods: UV-vis absorption, X-ray absorption, extended X-ray absorption fine structure and electron paramagnetic resonance. All three systems showed both a 1:1 and 2:1 ligand-Fe(III) stoichiometry, but presented different coordination properties. Conditional formation constants (pH approximately 2) were determined for both the 1:1 and 2:1 complexes in all three systems. Computation of the coordination-conformational energies by semiempirical methods indicated that the coordination in the case of the 2:1 complexes of pyochelin-Fe(III) and 3''-nor-NH-pyochelin-Fe(III) was asymmetrical, with one molecule of pyochelin (or 3''-nor-NH-pyochelin) tetradentately coordinated (O1, N1, N2 and O3) to the Fe(III), and the second molecule bound bidentately (O1, N1 or N2, O3), to complete the octahedral geometry. In contrast, two molecules of the methyl hydroxamate each provided a set of tridentate ligand atoms in the formation of the 2:1 ligand-Fe(III) complex. These results are consistent with the role of pyochelin in the uptake of iron by the FptA receptor in the outer membrane of Pseudomonas aeruginosa and in several gram-negative bacteria.
Biochemical and Biophysical Research Communications, 2008
Leishmaniasis is a tropical disease caused by Leishmania, eukaryotic parasites transmitted to hum... more Leishmaniasis is a tropical disease caused by Leishmania, eukaryotic parasites transmitted to humans by sand flies. Towards the development of new chemotherapeutic targets for this disease, biochemical and in vivo expression studies were performed on one of two M32 carboxypeptidases present within the Leishmania major (LmaCP1) genome. Enzymatic studies reveal that like previously studied M32 carboxypeptidases, LmaCP1 cleaves substrates with a variety of C-terminal amino acids-the primary exception being those having C-terminal acidic residues. Cleavage assays with a series of FRETbased peptides suggest that LmaCP1 exhibits a substrate length restriction, preferring peptides shorter than 9-12 amino acids. The in vivo expression of LmaCP1 was analyzed for each major stage of the L. major life cycle. These studies reveal that LmaCP1 expression occurs only in procyclic promastigotes-the stage of life where the organism resides in the abdominal midgut of the insect. The implications of these results are discussed.
Energy Environ. Sci.
The development of a heterogeneous catalyst capable for efficient selective conversion of methane... more The development of a heterogeneous catalyst capable for efficient selective conversion of methane into methanol with multiple turnovers under ambient conditions is reported here.
Biochemistry, 1990
The electrons enter the protein from the cytosol side of the mitochondrial inner membrane, and th... more The electrons enter the protein from the cytosol side of the mitochondrial inner membrane, and the protons consumed in the dioxygen reduction reaction are taken up from the matrix. In this manner, the sidedness of the membrane is exploited to convert redox free energy into a ...
Proceedings of the National Academy of Sciences, Apr 1, 1970
The nature of the intramolecular hydrogen bond in the enol tautomer of 2, 4-pentanedione has been... more The nature of the intramolecular hydrogen bond in the enol tautomer of 2, 4-pentanedione has been investigated by high resolution proton and deuteron magnetic resonance spectroscopy. An unusually large deuterium isotope effect on the chemical shift of the bridge hydrogen has been observed. This unexpected result, together with the observation of a pronounced temperature dependence for both the proton and deuteron resonances, suggests that two states with different chemical shifts for the bridge hydrogen ...
Biochemistry, Apr 20, 2004
The particulate methane monooxygenase (pMMO) is a complex membrane protein complex that has been ... more The particulate methane monooxygenase (pMMO) is a complex membrane protein complex that has been difficult to isolate and purify for biochemical and biophysical characterization because of its instability in detergents used to solubilize the enzyme. In this perspective, we summarize the progress recently made toward obtaining a purified pMMO-detergent complex and characterizing the enzyme in pMMO-enriched membranes. The purified pMMO is a multi-copper protein, with ca. 15 copper ions sequestered into five trinuclear copper ...
Angewandte Chemie International Edition