Journal article
Protein thermal denaturation, side-chain models, and evolution: amino acid substitutions at a conserved helix-helix interface
Biochemistry (Easton), v 34(10), pp 3268-3276
14 Mar 1995
PMID: 7880822
Featured in Collection : UN Sustainable Development Goals @ Drexel
Abstract
Random mutant libraries with substitutions at the interface between the N- and C-terminal helices of Saccharomyces cerevisiae iso-1-cytochrome c were screened. All residue combinations that have been identified in naturally occurring cytochrome c sequences are found in the libraries. Mutants with these combinations are biologically functional. Enthalpies, heat capacities, and midpoint temperatures of denaturation are used to determine the entropy and Gibbs free energy of denaturation (AGd) for the fern form of the wild-type protein and 13 interface variants. Changes in AGd cannot be allocated solely to enthalpic or entropic effects, but there is no evidence of enthalpy—entropy compensation. The lack of additivity of AGd values for single versus multiple amino acid substitutions indicates that the helices interact thermodynamically. Changes in AGd are not in accord with helix propensities, indicating that interactions between the helices and the rest of the protein outweigh helix propensity. Comparison of AGd values for the interface variants and nearly 90 non-cytochrome c variants to side-chain model data leads to several conclusions. First, hydrocarbon side chains react to burial-like transfer from water to cyclohexane, but even weakly polar side chains respond differently. Second, despite octanol being a poor model for protein interiors, octanol-to-water transfer free energies are useful stability predictors for changing large hydrocarbon side chains to smaller ones. Third, unlike cyclohexane and octanol, the Dayhoff mutation matrix predicts stability changes for a variety of substitutions, even at interacting sites. Furthermore, a correlation is observed between stability changes and the growth rates of yeast harboring the variants. In relation to protein evolution, interface variants possessing residue combinations found in naturally occurring cytochrome c sequences are the most stable, and the data support the neutral theory of macromolecular evolution
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Details
- Title
- Protein thermal denaturation, side-chain models, and evolution: amino acid substitutions at a conserved helix-helix interface
- Creators
- Gary J PielakDouglas S AuldJames R BeasleyStephen F BetzDavid S CohenDonald F DoyleShelley A FingerZoey L Fredericks - Duke UniversitySharon Hilgen-Willis - California University of PennsylvaniaAleister J Saunders - BiologySonja K. Trojak - University of North Carolina at Chapel Hill
- Publication Details
- Biochemistry (Easton), v 34(10), pp 3268-3276
- Publisher
- American Chemical Society; Washington, DC
- Number of pages
- 9
- Resource Type
- Journal article
- Language
- English
- Academic Unit
- Biology
- Web of Science ID
- WOS:A1995QM33300017
- Scopus ID
- 2-s2.0-0028920911
- Other Identifier
- 991021448039204721
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- Web of Science research areas
- Biochemistry & Molecular Biology