Khoshnoodi Jamshid, Sigmundsson Kristmundur, Cartailler Jean-Philippe, Bondar Olga, Sundaramoorthy Munirathinam, Hudson Billy G
Department of Medicine, Vanderbilt University School of Medicine, Medical Center, 1161 21st Avenue South, Nashville, TN 37232, USA.
J Biol Chem. 2006 Mar 3;281(9):6058-69. doi: 10.1074/jbc.M506555200. Epub 2005 Dec 22.
Collagens comprise a large superfamily of extracellular matrix proteins that play diverse roles in tissue function. The mechanism by which newly synthesized collagen chains recognize each other and assemble into specific triple-helical molecules is a fundamental question that remains unanswered. Emerging evidence suggests a role for the non-collagenous domain (NC1) located at the C-terminal end of each chain. In this study, we have investigated the molecular mechanism underlying chain selection in the assembly of collagen IV. Using surface plasmon resonance, we have determined the kinetics of interaction and assembly of the alpha1(IV) and alpha2(IV) NC1 domains. We show that the differential affinity of alpha2(IV) NC1 domain for dimer formation underlies the driving force in the mechanism of chain discrimination. Given its characteristic domain recognition and affinity for the alpha1(IV) NC1 domain, we conclude that the alpha2(IV) chain plays a regulatory role in directing chain composition in the assembly of (alpha1)(2)alpha2 triple-helical molecule. Detailed crystal structure analysis of the (alpha1)(2)alpha2 NC1 hexamer and sequence alignments of the NC1 domains of all six alpha-chains from mammalian species revealed the residues involved in the molecular recognition of NC1 domains. We further identified a hypervariable region of 15 residues and a beta-hairpin structural motif of 13 residues as two prominent regions that mediate chain selection in the assembly of collagen IV. To our knowledge, this report is the first to combine kinetics and structural data to describe molecular basis for chain selection in the assembly of a collagen molecule.
胶原蛋白构成了一个庞大的细胞外基质蛋白超家族，在组织功能中发挥着多种作用。新合成的胶原链相互识别并组装成特定三螺旋分子的机制是一个尚未得到解答的基本问题。新出现的证据表明，位于每条链C末端的非胶原结构域（NC1）发挥了作用。在本研究中，我们调查了IV型胶原组装过程中链选择的分子机制。利用表面等离子体共振，我们确定了α1(IV)和α2(IV) NC1结构域相互作用和组装的动力学。我们表明，α2(IV) NC1结构域对二聚体形成的差异亲和力是链区分机制中的驱动力。鉴于其对α1(IV) NC1结构域的特征性结构域识别和亲和力，我们得出结论，α2(IV)链在指导(α1)₂α2三螺旋分子组装中的链组成方面发挥调节作用。[(α1)₂α2]₂ NC1六聚体的详细晶体结构分析以及来自哺乳动物物种的所有六条α链的NC1结构域的序列比对揭示了参与NC1结构域分子识别的残基。我们进一步确定了一个由15个残基组成的高变区和一个由13个残基组成的β发夹结构基序，作为IV型胶原组装过程中介导链选择的两个突出区域。据我们所知，本报告首次结合动力学和结构数据来描述胶原分子组装中链选择的分子基础。
