Kirszbaum L, Sharpe J A, Murphy B, d'Apice A J, Classon B, Hudson P, Walker I D
Department of Veterinary Preclinical Sciences, University of Melbourne, Victoria, Australia.
EMBO J. 1989 Mar;8(3):711-8. doi: 10.1002/j.1460-2075.1989.tb03430.x.
The cDNA sequence encoding the human complement-associated protein, SP-40,40, is reported. The two chains of SP-40,40 are coded in a single open reading frame on the same mRNA molecule, indicating the existence of a biosynthetic precursor protein which matures post-synthetically by the proteolysis of at least one peptide bond. The precursor is preceded by a signal sequence for vectorial export and contains six N-linked glycosylation sites distributed equally between the two chains of the structure. The sequence of the SP-40,40 precursor bears a 77% identity to a rat sulphated glycoprotein-2 (SGP-2) which is the major secreted product of Sertoli cells. The presence of SP-40,40 within human seminal plasma at levels comparable to those in serum was demonstrated, indicating that SP-40,40 and SGP-2 are serum and seminal forms of the same protein. A sequence of 23 amino acids within the beta-chain of SP-40,40 exhibited significant homology to corresponding segments located within complement components C7, C8 and C9. The short cysteine-containing motif represented the only evidence of a possible vestigial relationship between SP-40,40 and other complement components. The precise role of SP-40,40 is not known in either blood or semen but the present findings document an intriguing link between the immune and the reproductive systems.
已报道了编码人补体相关蛋白SP-40,40的cDNA序列。SP-40,40的两条链由同一mRNA分子上的单一开放阅读框编码，这表明存在一种生物合成前体蛋白，该前体蛋白在合成后通过至少一个肽键的蛋白水解作用而成熟。该前体蛋白之前有一个用于定向输出的信号序列，并包含六个N-连接糖基化位点，在结构的两条链之间平均分布。SP-40,40前体蛋白的序列与大鼠硫酸化糖蛋白-2（SGP-2）具有77%的同一性，SGP-2是支持细胞的主要分泌产物。已证实在人精浆中存在与血清中水平相当的SP-40,40，这表明SP-40,40和SGP-2是同一蛋白的血清和精浆形式。SP-40,40β链内一段23个氨基酸的序列与补体成分C7、C8和C9内的相应片段表现出显著的同源性。这个含半胱氨酸的短基序是SP-40,40与其他补体成分之间可能存在残余关系的唯一证据。SP-40,40在血液或精液中的具体作用尚不清楚，但目前的研究结果证明了免疫系统和生殖系统之间存在着有趣的联系。
