FUNCTIONAL DIVERSIFICATION AND EVOLUTION OF ANTIFREEZE PROTEINS

这个子项目是利用资源的许多研究子项目之一。 由NIH/NCRR资助的中心拨款提供。对子项目的主要支持 子项目的首席调查员可能是由其他来源提供的， 包括美国国立卫生研究院的其他来源。为子项目列出的总成本可能 表示该子项目使用的中心基础设施的估计数量， 不是由NCRR赠款提供给次级项目或次级项目工作人员的直接资金。 抗冻蛋白(AFP)在许多生物体中独立进化。AFPS通过与冰晶结合，有效地降低冰点。AFP在基因组中通常具有较高的拷贝数，并且拷贝之间存在多样性。在北极和南极的鳗鱼嘴巴中发现了III型抗冻蛋白，此前已有研究表明，它们在正向选择下会进化。在这里，我们结合分子和蛋白质组学技术来了解单个南极鱼Lycodichthys dearborni的III型抗冻蛋白的分子进化和多样性。我们的表达序列标签(EST)屏幕显示，至少有七种不同的AFP变体被转录，这些变体最终被翻译成五种不同的蛋白质亚型。异构体具有相同的66个碱基对信号序列和不同数量的后续冰结合结构域，后面跟着一个终止密码子。EST文库中存在具有一个冰结合单元(单体)、两个单元(二聚体)和多个单元(多聚体)的异构体。我们发现了一种以前未知的蛋白质二聚体，这进一步证明了III型AFP亚型之间存在多样性，这可能是由于对更大热滞的积极选择所致。蛋白质组学分析证实，其中几种异构体被翻译并存在于肝脏中。我们的分子进化研究表明，在正选择的情况下，对虾已经发生了分化。我们假设抗冻蛋白的多样性是降低血清冰点的重要因素。

This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. Primary support for the subproject and the subproject's principal investigator may have been provided by other sources, including other NIH sources. The Total Cost listed for the subproject likely represents the estimated amount of Center infrastructure utilized by the subproject, not direct funding provided by the NCRR grant to the subproject or subproject staff. Antifreeze proteins (AFPs) have independently evolved in many organisms. AFPs act by binding to ice crystals, effectively lowering the freezing point. AFPs are often at high copy number in a genome and diversity exists between copies. Type III antifreeze proteins are found in Arctic and Antarctic eel pouts, and have previously been shown to evolve under positive selection. Here we combine molecular and proteomic techniques to understand the molecular evolution and diversity of Type III antifreeze proteins in a single individual Antarctic fish Lycodichthys dearborni. Our expressed sequence tag (EST) screen reveals that at least seven different AFP variants are transcribed, which are ultimately translated into five different protein isoforms. The isoforms have identical 66 base pair signal sequences and different numbers of subsequent ice-binding domains followed by a stop codon. Isoforms with one ice-binding unit (monomer), two units (dimer), and multiple units (multimer) were present in the EST library. We identify a previously uncharacterized protein dimer, providing further evidence that there is diversity between Type III AFP isoforms, perhaps driven by positive selection for greater thermal hysteresis. Proteomic analysis confirms that several of these isoforms are translated and present in the liver. Our molecular evolution study shows that paralogs have diverged under positive selection. We hypothesize that antifreeze protein diversity is an important contributor to depressing the serum freezing point.