Nymalm Yvonne, Puranen J Santeri, Nyholm Thomas K M, Käpylä Jarmo, Kidron Heidi, Pentikäinen Olli T, Airenne Tomi T, Heino Jyrki, Slotte J Peter, Johnson Mark S, Salminen Tiina A
Department of Biochemistry and Pharmacy, Abo Akademi University, P.O. Box 66, FIN-20521, Turku, Finland.
J Biol Chem. 2004 Feb 27;279(9):7962-70. doi: 10.1074/jbc.M312912200. Epub 2003 Dec 4.
Integrin alpha(1)beta(1) is one of four collagen-binding integrins in humans. Collagens bind to the alphaI domain and in the case of alpha(2)I collagen binding is competitively inhibited by peptides containing the RKKH sequence and derived from the metalloproteinase jararhagin of snake venom from Bothrops jararaca. In alpha(2)I, these peptides bind near the metal ion-dependent adhesion site (MIDAS), where a collagen (I)-like peptide is known to bind; magnesium is required for binding. Published structures of the ligand-bound "open" conformation of alpha(2)I differs significantly from the "closed" conformation seen in the structure of apo-alpha(2)I near MIDAS. Here we show that two peptides, CTRKKHDC and CARKKHDC, derived from jararhagin also bind to alpha(1)I and competitively inhibit collagen I binding. Furthermore, calorimetric and fluorimetric measurements show that the structure of the complex of alpha(1)I with Mg(2+) and CTRKKHDC differs from structure in the absence of peptide. A comparison of the x-ray structure of apo-alpha(1)I ("closed" conformation) and a model structure of the alpha(1)I ("open" conformation) based on the closely related structure of alpha(2)I reveals that the binding site is partially blocked to ligands by Glu(255) and Tyr(285) in the "closed" structure, whereas in the "open" structure helix C is unwound and these residues are shifted, and the "RKKH" peptides fit well when docked. The "open" conformation of alpha(2)I resulting from binding a collagen (I)-like peptide leads to exposure of hydrophobic surface, also seen in the model of alpha(1)I and shown experimentally for alpha(1)I using a fluorescent hydrophobic probe.
整合素α(1)β(1)是人类四种胶原结合整合素之一。胶原蛋白与αI结构域结合，就α(2)I而言，来自巴西矛头蝮蛇毒金属蛋白酶jararhagin且含有RKKH序列的肽会竞争性抑制胶原蛋白结合。在α(2)I中，这些肽在金属离子依赖性粘附位点（MIDAS）附近结合，已知一种胶原蛋白（I）样肽在此处结合；结合需要镁。已发表的与配体结合的α(2)I“开放”构象的结构与在apo-α(2)I结构中MIDAS附近看到的“封闭”构象有显著差异。在这里我们表明，源自jararhagin的两种肽CTRKKHDC和CARKKHDC也与α(1)I结合并竞争性抑制胶原蛋白I结合。此外，量热法和荧光法测量表明，α(1)I与Mg(2+)和CTRKKHDC形成的复合物的结构与无肽时的结构不同。apo-α(1)I（“封闭”构象）的x射线结构与基于α(2)I密切相关结构的α(1)I（“开放”构象）模型结构的比较表明，在“封闭”结构中，Glu(255)和Tyr(285)会部分阻断配体的结合位点，而在“开放”结构中，螺旋C展开且这些残基发生移位，“RKKH”肽对接时契合良好。结合一种胶原蛋白（I）样肽产生的α(2)I“开放构象会导致疏水表面暴露，在α(1)I模型中也可见，并且使用荧光疏水探针通过实验在α(1)I中得到证实。
