Kjalke M, Welinder K G, Koch C
Department of Protein Chemistry, University of Copenhagen, Denmark.
J Immunol. 1993 Oct 15;151(8):4147-52.
Chicken complement factor B-like protease is a glycoprotein of 95 kDa. Activation of chicken serum complement with inulin cleaved the B-like protease into an N-terminal Ba fragment of 37 kDa and a C-terminal Bb fragment of 60 kDa. The whole protein and the two fragments were purified by affinity chromatography using mAb to chicken Ba or Bb followed by ion exchange chromatography. Amino acid sequencing showed that chicken B-like protease was cleaved at a site homologous to that cleaved in mammalian complement components B and C2 on activation. Limited tryptic digestion of the B-like protease generated fragments similar to Ba and Bb. More than 200 residues of the Ba sequence and two N-linked glycosylation sites were established by amino acid sequencing of peptides derived by digestion with four proteases. Comparison of human and mouse C2 and B sequences indicated a slower evolutionary rate for B (85% sequence identity) than for C2 (74% sequence identity). Comparison of chicken Ba to human and mouse C2b and Ba showed 42 to 45% sequence identity with respect to C2b fragments, and 46 to 49% sequence identity with respect to Ba fragments. Taking the slower evolutionary rate of factor B into account, chicken factor B-like protease seems to be equally related to mammalian complement components B and C2, and the B-like protease most likely represents the present-day descendant of a common ancestral protein for mammalian B and C2. This conclusion is in agreement with the requirement for the B-like protease in both classical and alternative activation pathways for chicken complement, and with the apparent lack of a chicken serum protein with exclusive C2 activity.
鸡补体因子B样蛋白酶是一种95 kDa的糖蛋白。用菊粉激活鸡血清补体可将B样蛋白酶切割成一个37 kDa的N端Ba片段和一个60 kDa的C端Bb片段。通过使用抗鸡Ba或Bb的单克隆抗体进行亲和层析，随后进行离子交换层析，对整个蛋白和两个片段进行了纯化。氨基酸测序表明，鸡B样蛋白酶在与哺乳动物补体成分B和C2激活时切割位点同源的位置被切割。对B样蛋白酶进行有限的胰蛋白酶消化产生了与Ba和Bb相似的片段。通过对用四种蛋白酶消化产生的肽段进行氨基酸测序，确定了Ba序列的200多个残基和两个N-连接糖基化位点。人与小鼠C2和B序列的比较表明，B的进化速率（序列同一性为85%）比C2（序列同一性为74%）慢。将鸡Ba与人及小鼠C2b和Ba进行比较，发现与C2b片段的序列同一性为42%至45%，与Ba片段的序列同一性为46%至49%。考虑到因子B进化速率较慢，鸡因子B样蛋白酶似乎与哺乳动物补体成分B和C2具有同等的相关性，并且B样蛋白酶很可能代表了哺乳动物B和C2共同祖先蛋白的现代后代。这一结论与鸡补体经典和替代激活途径中对B样蛋白酶的需求一致，也与明显缺乏具有唯一C2活性的鸡血清蛋白一致。
