Merritt T J, Quattro J M
Department of Biological Sciences, Program in Marine Science, Baruch Institute and School of the Environment, University of South Carolina, Columbia, 29208, USA.
Genetics. 2001 Oct;159(2):689-97. doi: 10.1093/genetics/159.2.689.
A striking correlation between neural expression and high net negative charge in some teleost isozymes led to the interesting, yet untested, suggestion that negative charge represents an adaptation (via natural selection) to the neural environment. We examine the evolution of the triosephosphate isomerase (TPI) gene family in fishes for periods of positive selection. Teleost fish express two TPI proteins, including a generally expressed, neutrally charged isozyme and a neurally expressed, negatively charged isozyme; more primitive fish express only a single, generally expressed TPI isozyme. The TPI gene phylogeny constructed from sequences isolated from two teleosts, a single acipenseriform, and other TPI sequences from the databases, supports a single gene duplication event early in the evolution of bony fishes. Comparisons between inferred ancestral TPI sequences indicate that the neural TPI isozyme evolved through a period of positive selection resulting in the biased accumulation of negatively charged amino acids. Further, the number of nucleotide changes required for the observed amino acid substitutions suggests that selection acted on the overall charge of the protein and not on specific key amino acids.
在一些硬骨鱼同工酶中，神经表达与高净负电荷之间存在显著相关性，这引发了一个有趣但未经检验的观点，即负电荷代表了（通过自然选择）对神经环境的一种适应。我们研究了鱼类磷酸丙糖异构酶（TPI）基因家族在正选择时期的进化情况。硬骨鱼表达两种TPI蛋白，包括一种普遍表达的、呈中性电荷的同工酶和一种在神经中表达的、带负电荷的同工酶；更原始的鱼类只表达一种单一的、普遍表达的TPI同工酶。从两种硬骨鱼、一种鲟形目鱼类以及数据库中的其他TPI序列分离出的序列构建的TPI基因系统发育树，支持在硬骨鱼进化早期发生了一次单一的基因复制事件。对推断的祖先TPI序列的比较表明，神经TPI同工酶是通过一段正选择时期进化而来的，导致带负电荷氨基酸的偏向性积累。此外，观察到的氨基酸替换所需的核苷酸变化数量表明，选择作用于蛋白质的整体电荷而非特定的关键氨基酸。
