EXTRAORDINARY DIVERGENCE AND POSITIVE DARWINIAN SELECTION IN A FUSAGENIC PROTEIN COATING THE ACROSOMAL PROCESS OF ABALONE SPERMATOZOA
EXTRAORDINARY DIVERGENCE AND POSITIVE DARWINIAN SELECTION IN A FUSAGENIC PROTEIN COATING THE ACROSOMAL PROCESS OF ABALONE SPERMATOZOA
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DOI：
10.1073/pnas.92.11.4957
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发表时间：
1995-05-23
影响因子：
11.1
通讯作者：
VACQUIER, VD
中科院分区：
文献类型：
--
作者：
SWANSON, WJ;VACQUIER, VD
在海洋无脊椎动物的受精过程中，精子和卵细胞膜之间的融合发生在精子顶体突起的顶端。在鲍鱼精子中，顶体突起被一种18-kDa的蛋白质包裹，这种蛋白质在原位上对卵黄被膜没有影响，但在体外它是一种强有力的脂质体融合因子，因此，18-kDa蛋白质可能介导配子之间的膜融合，这是配子识别中已知的限制其他物种异种受精的一个步骤。对核苷酸替换的分析表明，与沉默的替换相比，氨基酸改变替换的频率极高，这表明积极的达尔文选择促进了该蛋白质的分化，但氨基酸替换在残基的大小和极性上是保守的。这些数据支持这样的发展观点，即在自由产卵的海洋无脊椎动物中，介导受精的蛋白质可能受到强烈的、未知的选择性作用力，受精蛋白的异常差异可能与异种受精障碍的建立有关。
During fertilization in marine invertebrates, fusion between sperm and egg cell membranes occurs at the tip of the sperm acrosomal process. In abalone sperm the acrosomal process is coated with an 18-kDa protein, In situ, this protein has no effect on the egg vitelline envelope, but in vitro it is a potent fusagen of liposomes, Thus, the 18-kDa protein may mediate membrane fusion between the gametes, a step in gamete recognition known to restrict heterospecific fertilization in other species, The cDNA and deduced amino acid sequences of the 18-kDa protein were determined for five species of California abalone, The deduced amino acid sequences exhibit extraordinary divergence; the percent identity varies from 27% to 87%. Analysis of nucleotide substitution shows extremely high frequencies of amino acid-altering substitution compared to silent substitution, demonstrating that positive Darwinian selection promotes the divergence of this protein, However, amino acid replacement is conservative with respect to size and polarity of residue, The data support the developing idea that in free-spawning marine invertebrates, the proteins mediating fertilization may be subjected to intense, and as yet unknown, selective forces, The extraordinary divergence of fertilization proteins may be related to the establishment of barriers to heterospecific fertilization.