Shin Dong-Ho, Webb Barbara, Nakao Miki, Smith Sylvia L
Department of Biological Sciences, Florida International University, University Park, Miami, FL 33199, USA.
Dev Comp Immunol. 2007;31(11):1168-82. doi: 10.1016/j.dci.2007.03.001. Epub 2007 Apr 2.
Factor B and C2 are serine proteases that provide the catalytic subunits of C3 and C5 convertases of the alternative (AP) and classical (CP) complement pathways. Two Bf/C2 cDNAs, GcBf/C2-1 and -2 (previously referred to as nsBf/C2-A and nsBf/C2-B), were isolated from the nurse shark, Ginglymostoma cirratum. GcBf/C2-1 and -2 are 3364 and 3082bp in length and encode a leader peptide, three CCPs, one VWFA, the serine protease domain and have a putative factor D/C1s/MASP cleavage site. Southern blots show that there might be up to two Bf/C2-like genes for each of the two GcBf/C2 isoforms. GcBf/C2-1 and -2 are constitutively expressed, albeit at different levels, in all nine tissues examined. Expression in erythrocytes is a novel finding. Structural analysis has revealed that the localization of glycosylation sites in the SP domain of both putative proteins indicates that the molecular organization of the shark molecules is more like C2 than factor B. Phylogenetic analysis indicates that GcBf/C2-1 and -2 and TrscBf of Triakis scyllia (another shark species) originated from a common ancestor and share a remote ancestor with Bf and C2 of mammals and bony fish.
B因子和C2是丝氨酸蛋白酶，它们分别为替代补体途径（AP）和经典补体途径（CP）的C3和C5转化酶提供催化亚基。从护士鲨（Ginglymostoma cirratum）中分离出了两个Bf/C2 cDNA，即GcBf/C2-1和-2（以前称为nsBf/C2-A和nsBf/C2-B）。GcBf/C2-1和-2的长度分别为3364和3082bp，编码一个前导肽、三个补体控制蛋白（CCP）、一个von Willebrand因子A结构域（VWFA）、丝氨酸蛋白酶结构域，并具有一个假定的因子D/C1s/甘露聚糖结合凝集素相关丝氨酸蛋白酶（MASP）裂解位点。Southern印迹显示，这两种GcBf/C2同工型中的每一种可能都有多达两个类似Bf/C2的基因。在所检测的所有九个组织中，GcBf/C2-1和-2均持续表达，尽管表达水平不同。红细胞中的表达是一个新发现。结构分析表明，两种假定蛋白质的丝氨酸蛋白酶结构域（SP）中糖基化位点的定位表明，鲨鱼分子的分子组织更类似于C2而非B因子。系统发育分析表明，GcBf/C2-1和-2以及三角鲨（Triakis scyllia，另一种鲨鱼物种）的TrscBf起源于一个共同祖先，并与哺乳动物和硬骨鱼的Bf和C2共享一个远古祖先。
