Langen R, Isas J M, Hubbell W L, Haigler H T
Jules Stein Eye Institute and Department of Chemistry and Biochemistry, University of California, Los Angeles, CA 90095, USA.
Proc Natl Acad Sci U S A. 1998 Nov 24;95(24):14060-5. doi: 10.1073/pnas.95.24.14060.
Previous studies of the annexin family of Ca2+ binding proteins identified a soluble monomer in the absence of Ca2+ and a trimer adsorbed on the membrane surface in the presence of Ca2+. On the basis of site-directed spin-labeling studies of annexin XII at low pH, we now report a membrane-inserted form of the protein with a dramatically different structure. The data suggest that upon insertion a continuous transmembrane alpha-helix is reversibly formed from a helix-loop-helix motif in the solution structure. Other regions with similar membrane-insertion potential were identified in the amino acid sequence, and we propose that the corresponding helices come together to form an aqueous pore that mediates the ion channel activity reported for several annexins.
先前对钙结合蛋白膜联蛋白家族的研究发现，在没有钙离子的情况下会形成可溶性单体，而在有钙离子的情况下会形成吸附在膜表面的三聚体。基于在低pH值下对膜联蛋白XII进行的定点自旋标记研究，我们现在报告了一种结构截然不同的膜插入形式的该蛋白。数据表明，插入时，溶液结构中的螺旋-环-螺旋基序会可逆地形成连续的跨膜α螺旋。在氨基酸序列中还鉴定出了具有类似膜插入潜力的其他区域，我们推测相应的螺旋会聚集在一起形成一个水相孔道，介导几种膜联蛋白所报道的离子通道活性。
