title: Local stability identification and the role of key acidic amino acid residues in staphylococcal nuclease unfolding.
abstract: Staphylococcal nuclease is a single domain protein with 149 amino acids. It has no disulfide bonds, which makes it a simple model for the study of protein folding. In this study, 20 mutants of this protein were generated each with a single base substitution of glycine for negatively charged glutamic acid or aspartic acid. Using differential scanning microcalorimetry in thermal denaturation experiments, we identified two mutants, E75G and E129G, having approximately 43% and 44%, respectively, lower DeltaH(cal) values than the wild-type protein. Furthermore, two mutants, E75Q and E129Q, were created and the results imply that substitution of the Gly residue has little influence on destabilization of the secondary structure that leads to the large perturbation of the tertiary protein structure stability. Two local stable areas formed by the charge-charge interactions around E75 and E129 with particular positively charged amino acids are thus identified as being significant in maintenance of the three-dimensional structure of the protein.
authors.affiliation: Institute of BioAgricultural Sciences, Academia Sinica, Taipei, Taiwan.
authors.forename: Hueih-Min
authors.initials: HM
authors.lastname: Chen
authors.forename: Siu-Chiu
authors.initials: SC
authors.lastname: Chan
authors.forename: King-Wong
authors.initials: KW
authors.lastname: Leung
authors.forename: Jiun-Ming
authors.initials: JM
authors.lastname: Wu
authors.forename: Huey-Jen
authors.initials: HJ
authors.lastname: Fang
authors.forename: Tian Yow
authors.initials: TY
authors.lastname: Tsong
mesh_terms: D001224:Aspartic Acid / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D002152:Calorimetry, Differential Scanning; D002942:Circular Dichroism; D004795:Enzyme Stability / Q000502:physiology; D018698:Glutamic Acid / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D008836:Micrococcal Nuclease / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D009154:Mutation; D011489:Protein Denaturation / Q000502:physiology; D017510:Protein Folding; D017434:Protein Structure, Tertiary; D013050:Spectrometry, Fluorescence; D013696:Temperature; D013816:Thermodynamics
chemical_list: D001224:Aspartic Acid; D018698:Glutamic Acid; D008836:Micrococcal Nuclease