Department of Veterinary Science, Louisiana State University Agricultural Center, Baton Rouge, LA 70803, USA.
Comp Biochem Physiol B Biochem Mol Biol. 2011 Jan;158(1):9-22. doi: 10.1016/j.cbpb.2010.06.006. Epub 2010 Jul 1.
The major plasma protein of the eastern oyster, Crassostrea virginica, was purified, characterized and named dominin. SDS-PAGE analyses revealed that dominin consistently made up more than 40% of eastern oyster plasma and extrapallial fluid proteins. Three different forms of dominin were observed under non-reducing conditions. PCR and RACE primers designed from partial amino acid sequences obtained by tandem mass spectrometry of purified dominin identified 720bp of complete cDNA encoding 192 amino acid residues. Based on the deduced amino acid sequence of mature dominin, its molecular mass was calculated to be 19,389Da and was lower than the molecular mass of purified dominin measured by MALDI. This difference is likely due to post-translational modifications of dominin as the purified protein was found to be glycolysated, phosphorylated and likely sulfated. The amino acid sequence showed high similarity to the major plasma protein of the Pacific oyster (Crassostrea gigas), cavortin, and of the green-lipped mussel (Perna canaliculus), pernin, and to a recently described protein labeled as an extracellular superoxide dismutase from the Sydney rock oyster Saccostrea glomerata. While dominin was found to possess a Cu/Zn superoxide dismutase (SOD) domain, the domain was not completely conserved which explained why purified dominin lacked SOD activity. Dominin mRNA was detected in hemocytes by in situ hybridization and its expression measured by quantitative real time RT-PCR was significantly higher in winter than summer. Although the function(s) of dominin and homologous proteins is uncertain, the reported ability of cavortin to sequester iron and possibly limit the availability of this essential metal to pathogens suggests a potential role in host defense for this group of dominant plasma proteins. Other possible functions of dominin in antioxidation, wound repair, metal transport and shell mineralization are discussed leading us to conclude that dominin is likely a multifunctional protein.
东方牡蛎（Crassostrea virginica）的主要血浆蛋白已被纯化、鉴定并命名为 dominin。SDS-PAGE 分析表明，dominin 一直占东方牡蛎血浆和外套膜外液蛋白的 40%以上。在非还原条件下观察到三种不同形式的 dominin。从串联质谱法获得的纯化 dominin 的部分氨基酸序列设计的 PCR 和 RACE 引物鉴定出编码 192 个氨基酸残基的全长 cDNA 为 720bp。根据成熟 dominin 的推导氨基酸序列，其分子量计算为 19,389Da，低于 MALDI 测量的纯化 dominin 的分子量。这种差异可能是由于 dominin 的翻译后修饰所致，因为发现纯化蛋白发生了糖基化、磷酸化和可能的硫酸化。该氨基酸序列与太平洋牡蛎（Crassostrea gigas）的主要血浆蛋白 cavortin 和绿唇贻贝（Perna canaliculus）的 pernin 以及最近描述的一种标记为悉尼岩蚝（Saccostrea glomerata）细胞外超氧化物歧化酶的蛋白质具有高度相似性。虽然 dominin 被发现具有 Cu/Zn 超氧化物歧化酶（SOD）结构域，但该结构域不完全保守，这解释了为什么纯化的 dominin 缺乏 SOD 活性。原位杂交检测到 dominin mRNA 在血细胞中表达，实时定量 RT-PCR 测量其在冬季的表达显著高于夏季。虽然 dominin 和同源蛋白的功能尚不确定，但报道称 cavortin 能够螯合铁并可能限制病原体对这种必需金属的利用，这表明该组主要血浆蛋白在宿主防御中可能具有潜在作用。还讨论了 dominin 在抗氧化、伤口修复、金属转运和壳矿化中的其他可能功能，这使我们得出结论，dominin 可能是一种多功能蛋白。
