Intramolecular coevolution of amino acid sites has repeatedly been studied to improve predictions on protein structure and function. Thereby, the focus was on bacterial proteins with available crystallographic data. However, intramolecular coevolution has not yet been compared between protein sets along a gradient of functional proximity to fertilization. This is especially true for the potential effect of external selective forces on intraprotein coevolution. 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 proportions of covarying sites and more often resided at the cell membrane or were secreted. At the cellular level, they are thus closer to externally induced forces of postcopulatory selection which are known for their potential to increase substitution rates. In addition, we show that the intermediary status of the testicular protein set in correlation analyses is probably due to a special combination of reproductive and somatic involvements.

中文翻译：

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蛋白质内协同进化功能越来越接近受精

已经反复研究了氨基酸位点的分子内协同进化，以改进对蛋白质结构和功能的预测。因此，重点是具有可用晶体学数据的细菌蛋白质。然而，尚未在蛋白质组之间沿着功能接近受精的梯度比较分子内协同进化。对于外部选择力对蛋白质内共同进化的潜在影响尤其如此。在这项研究中，我们在代表精子、睾丸、全身和肝脏的相同大小的哺乳动物蛋白质组中研究了这两个方面。对于共同进化分析，我们从 10 个哺乳动物直向同源物的氨基酸比对中推导出每个蛋白质的共变位点的比例。为了确认我们共同进化代理的有效性，我们发现与所有蛋白质组中的非同义或氨基酸替代率呈正相关。然而，我们的共同进化代理仅与雄性生殖蛋白质组中蛋白质相互作用物的数量（节点度）呈负相关。此外，我们的共同进化代理与蛋白质疏水性的负相关仅在精子蛋白质中显着。因此，蛋白质相互作用物的限制作用在男性生殖蛋白质中最为明显，精子蛋白质形成内部结构的趋势越低，它们的共同进化位点越多。这两个方面都表明，外向和功能共同进化的份额随着受精的距离的增加而增加。我们发现通过精子蛋白质内的其他比较证实了这一结论。因此，具有高疏水性的精子蛋白具有最低比例的共变位点，并且根据基因注释，更频繁地定位于内部细胞结构。因此，它们应该较少地暴露于交配后的性选择形式。它们具有低疏水性的对应物具有更大比例的共变位点，并且更常驻留在细胞膜上或被分泌。因此，在细胞水平上，它们更接近于外部诱导的交配后选择力，后者以提高替代率的潜力而闻名。此外，我们表明相关分析中睾丸蛋白组的中间状态可能是由于生殖和躯体参与的特殊组合。更频繁地定位于内部细胞结构。因此，它们应该较少地暴露于交配后的性选择形式。它们具有低疏水性的对应物具有更大比例的共变位点，并且更常驻留在细胞膜上或被分泌。因此，在细胞水平上，它们更接近于外部诱导的交配后选择力，后者以提高替代率的潜力而闻名。此外，我们表明相关分析中睾丸蛋白组的中间状态可能是由于生殖和躯体参与的特殊组合。更频繁地定位于内部细胞结构。因此，它们应该较少地暴露于交配后的性选择形式。它们具有低疏水性的对应物具有更大比例的共变位点，并且更常驻留在细胞膜上或被分泌。因此，在细胞水平上，它们更接近于外部诱导的交配后选择力，后者以提高替代率的潜力而闻名。此外，我们表明相关分析中睾丸蛋白组的中间状态可能是由于生殖和躯体参与的特殊组合。它们具有低疏水性的对应物具有更大比例的共变位点，并且更常驻留在细胞膜上或被分泌。因此，在细胞水平上，它们更接近于外部诱导的交配后选择力，后者以提高替代率的潜力而闻名。此外，我们表明相关分析中睾丸蛋白组的中间状态可能是由于生殖和躯体参与的特殊组合。它们具有低疏水性的对应物具有更大比例的共变位点，并且更常驻留在细胞膜上或被分泌。因此，在细胞水平上，它们更接近于外部诱导的交配后选择力，后者以提高替代率的潜力而闻名。此外，我们表明相关分析中睾丸蛋白组的中间状态可能是由于生殖和躯体参与的特殊组合。