| Contributions of the polar, uncharged amino acids to the stability of staphylococcal nuclease: evidence for mutational effects on the free energy of the denatured state. | |
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MedLine Citation:
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PMID: 1610820 Owner: NLM Status: MEDLINE |
Abstract/OtherAbstract:
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In order to quantitate the contributions of the polar, uncharged amino acids to the stability of the native state of staphylococcal nuclease, each of the 13 alanines, 9 glycines, 9 threonines, 6 prolines, 6 glutamines, 6 asparagines, and 3 serines was substituted, either with both alanine and glycine or with 1 of these 2 amino acids plus valine. For each mutant, the stability to reversible denaturation (delta GH2O) was quantitated by determining the Kapp for this reaction as a function of guanidine hydrochloride concentration. In addition, the parameter mGuHCl (= d(delta G)/d[GuHCl]) was calculated from the data. To identify the local structural features responsible for the relatively large and variable changes in delta GH2O and mGuHCl observed for the same type of substitution at different locations in nuclease, statistical correlations were sought between delta GH2O, mGuHCl, and a number of descriptors of the local structure. As with substitutions of the large hydrophobic amino acids [Shortle, D., Stites, W. E., & Meeker, A. K. (1990) Biochemistry 29, 8033-8041], mutation of polar, uncharged residues to Gly leads to a change in stability that, on average, correlates well with the degree to which the wild-type residue is buried. This correlation is especially significant for threonine, an amino acid with both polar and hydrophobic character, but is not demonstrated for the more typically hydrophobic residue alanine. As reported in the previous study of alanine/glycine substitutions of hydrophobic residues, a significant correlation between changes in stability and changes in the value of mGuHCl is again observed, strengthening the conclusion that the putative structural changes in the denatured state which lead to increases or decreases in mGuHCl are responsible for a significant fraction of the stability loss for an average mutant. The existence of this correlation is consistent with the denatured state of wild-type staphylococcal nuclease having evolved to a relatively high free energy via optimization of a balance between a maximal exposure of hydrophobic surface and a minimal gain in chain entropy. On average, mutations are less stable in proportion to the extent of which they perturb this balance. A new and puzzling correlation is reported between the extent of buriedness of a residue in the wild-type native state versus the difference in mGuHCl between the Ala mutation and the Gly mutation at that position. |
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Authors:
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S M Green; A K Meeker; D Shortle |
Publication Detail:
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Type: Journal Article; Research Support, U.S. Gov't, P.H.S. |
Journal Detail:
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Title: Biochemistry Volume: 31 ISSN: 0006-2960 ISO Abbreviation: Biochemistry Publication Date: 1992 Jun |
Date Detail:
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Created Date: 1992-07-28 Completed Date: 1992-07-28 Revised Date: 2007-11-14 |
Medline Journal Info:
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Nlm Unique ID: 0370623 Medline TA: Biochemistry Country: UNITED STATES |
Other Details:
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Languages: eng Pagination: 5717-28 Citation Subset: IM |
Affiliation:
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Department of Biological Chemistry, Johns Hopkins University School of Medicine, Baltimore, Maryland 21205. |
Export Citation:
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APA/MLA Format Download EndNote Download BibTex |
| MeSH Terms | |
Descriptor/Qualifier:
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Alanine
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chemistry Amino Acid Sequence Amino Acids / chemistry* Enzyme Stability* Escherichia coli / enzymology Glycine / chemistry Guanidine Guanidines Micrococcal Nuclease / chemistry*, genetics Molecular Sequence Data Mutagenesis, Site-Directed* Protein Denaturation Thermodynamics |
| Grant Support | |
ID/Acronym/Agency:
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GM14306/GM/NIGMS NIH HHS; GM34171/GM/NIGMS NIH HHS |
| Chemical | |
Reg. No./Substance:
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0/Amino Acids; 0/Guanidines; 113-00-8/Guanidine; 56-40-6/Glycine; 56-41-7/Alanine; EC 3.1.31.1/Micrococcal Nuclease |
From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine
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