Document Detail

Selective constraints, amino acid composition, and the rate of protein evolution.
MedLine Citation:
PMID:  10742056     Owner:  NLM     Status:  MEDLINE    
What are the major forces governing protein evolution? A common view is that proteins with strong structural and functional requirements evolve more slowly than proteins with weak constraints, because a stringent negative selection pressure limits the number of substitutions. In contrast, Graur claimed that the substitution rate of a protein is mainly determined by its amino acid composition and the changeabilities of amino acids. In this paper, however, we found that the relative changeabilities of amino acids in mammalian proteins are different for transmembranal and nontransmembranal segments, which have very distinct structural requirements. This indicates that the changeability of a given residue is influenced by the structural and functional context. We also reexamined the relationship between substitution rate and amino acid composition. Indeed, the two kinds of segments exhibit contrasting amino acid compositions: transmembranal regions are made up mainly of hydrophobic residues (a total frequency of approximately 60%) and are very poor in polar amino acids (<5%), whereas nontransmembranal segments have frequencies of 30% and 22%, respectively. Interestingly, we found that within a given integral membrane protein, nontransmembranal segments accumulate, on average, twice as many substitutions as transmembranal regions. However, regression analyses showed that the variability in amino acid frequencies among proteins cannot explain more than 30% of the variability in substitution rate for the transmembranal and nontransmembranal data sets. Furthermore, transmembranal and nontransmembranal segments evolving at the same rate in different proteins have different compositions, and the compositions of slowly evolving and rapidly evolving segments of the same type are similar. From these observations, we conclude that the rate of protein evolution is only weakly affected by amino acid composition but is mostly determined by the strength of functional requirements or selective constraints.
N J Tourasse; W H Li
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Publication Detail:
Type:  Journal Article; Research Support, U.S. Gov't, P.H.S.    
Journal Detail:
Title:  Molecular biology and evolution     Volume:  17     ISSN:  0737-4038     ISO Abbreviation:  Mol. Biol. Evol.     Publication Date:  2000 Apr 
Date Detail:
Created Date:  2000-06-15     Completed Date:  2000-06-15     Revised Date:  2006-11-15    
Medline Journal Info:
Nlm Unique ID:  8501455     Medline TA:  Mol Biol Evol     Country:  UNITED STATES    
Other Details:
Languages:  eng     Pagination:  656-64     Citation Subset:  IM; S    
Department of Ecology and Evolution, University of Chicago, Illinois, USA.
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MeSH Terms
Amino Acid Substitution / genetics*
Evolution, Molecular*
Likelihood Functions
Mammals / genetics*
Proteins / genetics*
Sequence Alignment
Sequence Analysis, Protein
Reg. No./Substance:

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