Highly divergent dimorphic alleles of the proteasome subunit beta type-8 (PSMB8) gene of the bichir Polypterus senegalus : implication for evolution of the PSMB8 gene of jawed vertebrates
Highly divergent dimorphic alleles of the proteasome subunit beta type-8 (PSMB8) gene of the bichir Polypterus senegalus : implication for evolution of the PSMB8 gene of jawed vertebrates
复制标题
bichir Polypterus senegalus 蛋白酶体亚基 β 8 型 (PSMB8) 基因的高度分化二态性等位基因：对有颌脊椎动物 PSMB8 基因进化的影响
DOI：
10.1007/s00251-012-0602-8
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发表时间：
2012
期刊：
影响因子：
3.2
通讯作者：
Nonaka M
中科院分区：
文献类型：
--
作者：
Fujito NT;Nonaka M
蛋白酶体β8亚单位(PSMB8)基因编码免疫蛋白酶体的催化亚基，参与MHC I类分子呈递的多肽的产生。到目前为止，PSMB8的高度分化的二分等位基因已经在Oryzia物种(放线蕨类硬骨鱼)和Xenopus物种(石棺类两栖动物)中被报道。这些二态等位基因在成熟蛋白的第31位有相似的替换(A/V31F/Y)，这很可能与S1口袋的形成有关。这种替换可能赋予二晶型PSMB8不同的切割特异性。此外，在鲨鱼中已报道了两个在第31位具有A和F残基的PSMB8基因。系统发育分析表明，两种PSMB8是由独立的进化事件产生的。在这里，我们从基础放线蕨类Bichir，Polypterus senegalus中鉴定了另一对PSMB8的二态等位基因，其成熟蛋白第31位具有A和F残基。BichirPSMB8二态等位基因A型和F型的成熟蛋白编码区序列在核苷酸和氨基酸水平上的同源性分别为72.7%和77.5%。它们的内含子序列几乎没有相似性，表明BichirPSMB8的二态等位基因具有非常古老的起源。然而，系统发育分析表明，Bichir、Xenopus和Oryzia的PSMB8的二型性是由独立的进化事件引起的，这表明拥有这种二型性存在很强的选择压力。
The proteasome subunit beta type-8 (PSMB8) gene encodes a catalytic subunit of the immunoproteasome, which is involved in the generation of peptides presented by MHC class I molecules. To date, highly diverged dichotomous alleles ofPSMB8have been reported inOryziasspecies (actinopterygian teleosts) andXenopusspecies (sarcopterygian amphibians). These dimorphic alleles share a similar substitution (A/V31F/Y) at the 31st position of the mature protein, which is most probably involved in formation of the S1 pocket. This substitution likely confers different cleavage specificities on the dimorphic PSMB8s. In addition, two paralogousPSMB8genes possessing the A and F residues at the 31st position have been reported in sharks. Phylogenetic analysis indicated that the two types of PSMB8 ofOryzias,Xenopus, and sharks arose by independent evolutionary events. Here, we identified another pair of dimorphic alleles ofPSMB8, which have the A and F residues at the 31st position of the mature protein, from bichir,Polypterus senegalus, a basal actinopterygian. The sequences of the mature proteins-encoding region of the dimorphic alleles of bichirPSMB8, the A and F types, showed only 72.7% and 77.5% identities at the nucleotide and the deduced amino acid levels, respectively. Their intronic sequences show almost no similarity, indicating that the dimorphic alleles of bichirPSMB8have a very ancient origin. However, phylogenetic analysis showed that the dimorphisms ofPSMB8of bichir,Xenopus, andOryziasarose by independent evolutionary events, suggesting the presence of a strong selective pressure for possessing the dimorphism.