Hosokawa M, Nonaka M, Okada N, Nonaka M, Okada H
Department of Molecular Biology, Nagoya City University School of Medicine, Japan.
J Immunol. 1996 Dec 1;157(11):4946-52.
Human membrane cofactor protein (MCP) is a widely distributed cell-associated complement-regulatory protein, and recent findings suggest that MCP may be involved in sperm-egg interaction. We have isolated four cDNA clones and one reverse transcriptase-PCR product homologous to human MCP from guinea pig testis. These clones defined five isoform classes generated from a single copy gene by alternative splicing. Reverse transcriptase-PCR revealed that two classes for the clones termed GMP1 and GM2 were predominant. GMP1 consisted of four short consensus repeats (SCRs), regions corresponding to the human serine/threonine/proline-rich C (STP(C)) domain and a human region of unknown significance, a hydrophobic region presumed to be a transmembrane domain, and a cytoplasmic region. Identity with human MCP in the SCR region was 56% at the amino acid level and 71% at the nucleotide level. GM2 had the same structure as GMP1, except that it lacked the fourth SCR, which is presumed to be essential for C3b binding of human MCP. Northern blotting analysis of various tissues revealed a significant level of MCP transcripts in testis. Guinea pig MCP is likely to have only one STP domain that is homologous to human STP(C) and is similar in this respect to human spermatozoa MCP. Gene analysis revealed a single base deletion and a lack of consensus sequences for splicing in the guinea pig regions corresponding to human STP(A) and STP(B), respectively. These results suggest that guinea pig MCP plays a more restricted role in reproduction than does human MCP.
人膜辅因子蛋白（MCP）是一种广泛分布的细胞相关补体调节蛋白，最近的研究结果表明，MCP可能参与精卵相互作用。我们从豚鼠睾丸中分离出四个与人类MCP同源的cDNA克隆和一个逆转录酶-聚合酶链反应（RT-PCR）产物。这些克隆定义了由一个单拷贝基因通过可变剪接产生的五种同工型类别。逆转录酶-聚合酶链反应显示，名为GMP1和GM2的两个克隆类别占主导地位。GMP1由四个短共有重复序列（SCR）、对应于人类富含丝氨酸/苏氨酸/脯氨酸的C（STP（C））结构域的区域以及一个意义不明的人类区域、一个推测为跨膜结构域的疏水区域和一个细胞质区域组成。在SCR区域与人类MCP的氨基酸水平同一性为56%，核苷酸水平同一性为71%。GM2与GMP1结构相同，只是缺少第四个SCR，推测该SCR对人类MCP结合C3b至关重要。对各种组织的Northern印迹分析显示，睾丸中MCP转录本水平显著。豚鼠MCP可能只有一个与人类STP（C）同源的STP结构域，在这方面与人类精子MCP相似。基因分析显示，在豚鼠中分别对应于人类STP（A）和STP（B）的区域存在一个单碱基缺失和缺乏剪接共有序列的情况。这些结果表明，豚鼠MCP在生殖中的作用比人类MCP更有限。
