Rousseau J C, Farjanel J, Boutillon M M, Hartmann D J, van der Rest M, Moradi-Améli M
Institut de Biologie et Chimie des Protéines, UPR412 CNRS, 7 Passage du Vercors, F-69367 Lyon Cedex 7, France.
J Biol Chem. 1996 Sep 27;271(39):23743-8. doi: 10.1074/jbc.271.39.23743.
Type XI collagen is mainly found as a minor constituent in type II-containing fibrils and presents a alpha1(XI)alpha2(XI)alpha3(XI) stoichiometry. This molecule was shown to be partially processed in its intact tissue form. Moreover, alternative splicing has been demonstrated in the variable region of the N-terminal domain of alpha1(XI) and alpha2(XI) chains. In this work, the processing of a major intact form of alpha1(XI) from matrix laid down by chick chondrocytes in culture was identified using N-terminal sequencing and antibodies to synthetic peptides corresponding to the N-terminal propeptide cDNA-derived sequence. The results show that the fully processed form of alpha1(XI) begins at Gln254 of the N-terminal propeptide, seven residues before the end of the proline/arginine-rich protein region encoded by exon I (Zhidkova, N. I., Justice, S. K., and Mayne, R. (1995) J. Biol. Chem. 270, 9486-9493). This sequence is immediately followed by a sequence encoded by exon III. The processing takes place at an Ala-Gln sequence that corresponds to a consensus sequence for procollagen N-proteinase. The antibody raised against a sequence located within the region corresponding to exon IV (anti-P8) fails to recognize this fully processed form of the alpha1(XI) chain. It recognizes, however, two minor bands of high molecular mass. These results suggest that a major cartilage form of alpha1(XI) is the product of alternative splicing in which sequences encoded by both exons II and IV are skipped. The presence of a highly acidic subdomain encoded by exon III at the N terminus of the major form of the alpha1(XI) chain, as predicted by these data, provides potential sites for interaction of collagen XI with other molecules.
XI型胶原蛋白主要作为含II型纤维的次要成分被发现，其化学计量比为α1(XI)α2(XI)α3(XI)。该分子在其完整的组织形式中显示为部分加工状态。此外，已证实在α1(XI)和α2(XI)链的N端结构域可变区存在可变剪接。在这项工作中，使用N端测序以及针对与N端前肽cDNA衍生序列对应的合成肽的抗体，鉴定了培养的鸡软骨细胞分泌的基质中主要完整形式的α1(XI)的加工过程。结果表明，α1(XI)的完全加工形式始于N端前肽的Gln254，在由外显子I编码的富含脯氨酸/精氨酸的蛋白质区域末端前七个残基处（Zhidkova, N. I., Justice, S. K., and Mayne, R. (1995) J. Biol. Chem. 270, 9486 - 9493）。该序列紧接着是由外显子III编码的序列。加工发生在一个Ala - Gln序列处，该序列对应于原胶原蛋白N蛋白酶的共有序列。针对位于与外显子IV对应的区域内的序列产生的抗体（抗P8）无法识别α1(XI)链的这种完全加工形式。然而，它识别出两条高分子量的次要条带。这些结果表明，α1(XI)的一种主要软骨形式是可变剪接的产物，其中外显子II和IV编码的序列均被跳过。如这些数据所预测，在α1(XI)链主要形式的N端存在由外显子III编码的高度酸性亚结构域，为胶原蛋白XI与其他分子的相互作用提供了潜在位点。
