J chain in the nurse shark: Implications for function in a lower vertebrate
J chain in the nurse shark: Implications for function in a lower vertebrate
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DOI：
10.4049/jimmunol.170.12.6016
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发表时间：
2003-06-15
影响因子：
4.4
通讯作者：
Steiner, LA
中科院分区：
文献类型：
--
作者：
Hohman, VS;Stewart, SE;Steiner, LA
J链是共价连接到多聚伊加和IgM的小多肽。在人类和小鼠中，其在将IG结合到聚合物IG受体以转运到分泌物中起作用。通过对哺乳动物J链的cDNA序列和从IgM中分离的多肽序列的分析，在护士鲨中鉴定了假定的哺乳动物J链的直向同源物。与其他物种的J链的保守性相对较差，特别是在羧基末端部分，并且与其他J链不同，鲨鱼蛋白质不是酸性的。在所有已知的J链中唯一高度保守的片段是围绕N-连接的糖基化位点的残基块。在哺乳动物J链中保守的8个半胱氨酸残基中，有3个在护士鲨中缺乏，其中包括2个在羧基末端片段中，据报道这2个片段是含有人J链的伊加与分泌组分结合所必需的。结合这些数据，脾脏中J链转录本的相对丰度和螺旋瓣（肠）中的缺失表明护士鲨中的J链可能在IG分泌中没有作用。J链序列在不同物种的分析是一致的公认的系统发育关系，与例外的无脊椎动物，这表明报告的J链在无脊椎动物中的存在应重新评估。
J chain is a small polypeptide covalently attached to polymeric IgA and IgM. In humans and mice, it plays a role in binding Ig to the polymeric Ig receptor for transport into secretions. The putative orthologue of mammalian J chain has been identified in the nurse shark by sequence analysis of cDNA and the polypeptide isolated from IgM. Conservation with J chains from other species is relatively poor, especially in the carboxyl-terminal portion, and, unlike other J chains, the shark protein is not acidic. The only highly conserved segment in all known J chains is a block of residues surrounding an N-linked glycosylation site. Of the eight half-cystine residues that are conserved in mammalian J chains, three are lacking in the nurse shark, including two in the carboxyl-terminal segment that have been reported to be required for binding of human J chain-containing IgA to secretory component. Taken together with these data, the relative abundance of J chain transcripts in the spleen and their absence in the spiral valve (intestine) suggest that J chain in nurse sharks may not have a role in Ig secretion. Analysis of J chain sequences in diverse species is in agreement with accepted phylogenetic relationships, with the exception of the earthworm, suggesting that the reported presence of J chain in invertebrates should be reassessed.