title: Excessive homoplasy in an evolutionarily constrained protein.
abstract: The evolution of monomorphic proteins among closely related species has not been examined in detail. To investigate this phenomenon, the glycerol-3-phosphate dehydrogenase (Gpdh) locus was sequence in a broad range of Drosophila species. Although purifying selection to remove amino acid variation is the dominant force in the evolution of Gpdh, some replacements have occurred. The sequences were compared in the context of the phylogeny of the genus, revealing a high proportion of amino acid parallelism and reversal (homoplasy) at four sites. The level of homoplasy is significantly greater than that seen in other proteins for which multiple sequences are available, showing that Gpdh is strongly constrained by both the number of amino acid differences and the types of changes allowed. These four sites evolve at a much higher rate than do the other variable positions in the protein, accounting for half of the interspecific amino acid replacements. However, unlike typical hypervariable sites, where multiple changes to several different amino acids are seen, evolutionary 'flip-flopping' between two amino acid states defines this new class of hypervariable site.
authors.affiliation: Museum of Comparative Zoology Laboratories, Harvard University, Cambridge, Massachusetts 02138, USA.
authors.forename: R S
authors.initials: RS
authors.lastname: Wells
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D004330:Drosophila / Q000201:enzymology* / Q000235:genetics*; D019143:Evolution, Molecular; D014644:Genetic Variation; D005993:Glycerolphosphate Dehydrogenase / Q000235:genetics*; D006801:Humans; D008969:Molecular Sequence Data; D009154:Mutation; D010802:Phylogeny; D011506:Proteins / Q000235:genetics*; D017386:Sequence Homology, Amino Acid; D013045:Species Specificity
chemical_list: D011506:Proteins; D005993:Glycerolphosphate Dehydrogenase