Elucidation of activation mechanism of the lectin complement pathway

甘露糖结合凝集素(MBL，又称MBP)与两种结构上同源的丝氨酸蛋白酶MASP-1和MASP-2有关。当与病原体上的甘露糖等碳水化合物结合时，MBL-MASP复合体激活凝集素补体途径。本研究旨在阐明凝集素途径的激活机制。我们获得了以下结果：1)MBL-MASP制剂中存在一个22 kDa的蛋白(SMAP)，并与MASP-1相关。SMAP的cDNA分析表明SMAP是由MASP-2基因交替多聚腺化而来的。2)我们建立了人血清中MASP-1水平的酶联免疫吸附试验，发现MASP-1和MASP-1在个体中的水平没有相关性，MASP-1以MBL结合和MBL非结合的形式存在，后者与SMAP部分相关。3)MASP-1和MASP-2分别对C3和C4具有蛋白分解活性。4)MBL以不同大小的均聚物存在。对其中一种MBL均聚物的分析表明，它与MASP-1和SMAP共混，但不与MASP-2共混。

Mannose-binding lectin (MBL, also called MBP) is associated with two types of serine protease, MASP-1 and MASP-2, which are structually homologous. Upon binding to carbohydrates such as mannose on pathogens, the MBL-MASP complex activates the lectin complement pathway. The aim of this research was to elucidate the activation mechamism of the lectin pathway. We obtained the following results.1) A 22kDa protein (sMAP) is present in an MBL-MASP preparation and is associated with MASP-1. cDNA analysis of sMAP revealed that sMAP is derived from the MASP-2 gene by alternative polyadenylation.2) We developed an ELISA for MASP-1 levels in human serum and found that MBL and MASP-1 levels in serum are not correlated in the individual, and that MASP-1 exists as MBL-bound and MBL-unbound forms, the latter of which is associated with sMAP in part.3) MASP-1 and MASP-2 exhibit proteolytic activities towards C3 and C4, respectively.4) MBL exists as a homopolymer with various sizes. Analysis of one of MBL homopolymers revealed that it copurified with MASP-1 and sMAP but not with MASP-2.