Intra-Protein Coevolution Is Increasingly Functional with Greater Proximity to Fertilization

In this study, we investigated both aspects in equally sized sets of mammalian proteins representing spermatozoa, testis, entire body, and liver. For coevolutionary analyses, we derived the proportion of covarying sites per protein from amino acid alignments of 10 mammalian orthologues each. In confirmation of the validity of our coevolution proxy, we found positive associations with the nonsynonymous or amino acid substitution rate in all protein sets. However, our coevolution proxy negatively correlated with the number of protein interactants (node degree) in male reproductive protein sets alone. In addition, a negative association of our coevolution proxy with protein hydrophobicity was significant in sperm proteins only. Accordingly, the restrictive effect of protein interactants was most pronounced in male reproductive proteins, and the tendency of sperm proteins to form internal structures decreased the more coevolutionary sites they had. Both aspects illustrate that the share of outward and thus functional coevolution increases with greater proximity to fertilization. We found this conclusion confirmed by additional comparisons within sperm proteins. Thus, sperm proteins with high hydrophobicity had the lowest proportions of covarying sites and, according to gene annotations, localized more frequently to internal cellular structures. They should therefore be less exposed to postcopulatory forms of sexual selection. Their counterparts with low hydrophobicity had larger ...
Source: Cytogenetic and Genome Research - Category: Genetics & Stem Cells Source Type: research