Lambris J D, Ganu V S, Hirani S, Müller-Eberhard H J
Proc Natl Acad Sci U S A. 1985 Jun;82(12):4235-9. doi: 10.1073/pnas.82.12.4235.
The C3d domain of C3 contains the site that binds to the C3d receptor (CR2) which is expressed on B lymphocytes. It also contains a neoantigenic determinant that is recognized by monoclonal antibody (mAb) 130 and is expressed when C3b is cleaved to iC3b and subsequently to C3dg or C3d. mAb 130 inhibits the binding of C3d to CR2. In this study, the locations of the CR2-binding site and of the neoantigen recognized by mAb 130 within the C3d domain were investigated. Treatment of human C3d with CNBr generated two major fragments with Mrs of 12,500 and 8600. Binding studies showed that only the Mr 8600 fragment was capable of binding to both CR2 and mAb 130. Amino-terminal sequence analysis of the Mr 8600 fragment and comparison with the amino acid sequence derived from human C3 cDNA [de Bruijn, M. H. L. & Fey, G. H. (1985) Proc. Natl. Acad. Sci. USA 82, 708-712] placed it between residues 1199 and 1274 of the C3 sequence. Several peptides were synthesized according to the derived C3 sequence of amino acid residues 1209-1236. Based on their differential binding to CR2 and mAb 130, we localized the CR2-binding site and mAb 130 neoantigenic site, respectively, to residues 1227-1232 and 1217-1232 of the C3 sequence.
补体C3的C3d结构域包含与B淋巴细胞上表达的C3d受体（CR2）结合的位点。它还包含一个新抗原决定簇，可被单克隆抗体（mAb）130识别，当C3b裂解为iC3b，随后再裂解为C3dg或C3d时该决定簇会表达。mAb 130可抑制C3d与CR2的结合。在本研究中，对C3d结构域内CR2结合位点以及mAb 130识别的新抗原的位置进行了研究。用溴化氰处理人C3d产生了两个主要片段，分子量分别为12,500和8600。结合研究表明，只有分子量为8600的片段能够与CR2和mAb 130结合。对分子量为8600的片段进行氨基末端序列分析，并与源自人C3 cDNA的氨基酸序列进行比较[德布鲁因，M. H. L. & 费伊，G. H.（1985年）《美国国家科学院院刊》82, 708 - 712]，将其定位在C3序列的第1199至1274位残基之间。根据推导的C3序列中第1209 - 1236位氨基酸残基合成了几种肽。基于它们与CR2和mAb 130的不同结合情况，我们分别将CR2结合位点和mAb 130新抗原位点定位到C3序列的第1227 - 1232位残基和第1217 - 1232位残基。
