Langen R, Isas J M, Luecke H, Haigler H T, Hubbell W L
Jules Stein Eye Institute and Department of Chemistry and Biochemistry, University of California, Los Angeles, California 90095, USA.
J Biol Chem. 1998 Aug 28;273(35):22453-7. doi: 10.1074/jbc.273.35.22453.
Annexins are soluble proteins that bind to membranes in the presence of Ca2+. Crystal structures have been determined for some soluble forms, but little is known about the important membrane-bound state. We employed site-directed spin labeling to demonstrate that 1) annexin XII assumes a trimer configuration similar to the crystal structure when bound to bilayers under physiological conditions; 2) trimer assembly on bilayers is remarkably rapid, occurring on a millisecond time scale, whereas subunit exchange requires hours; and 3) different annexins can mix to form heterotrimers. The rapid assembly and heterotrimer formation have important implications concerning the cellular functions of annexins.
膜联蛋白是一类在Ca2+存在时能与膜结合的可溶性蛋白质。已确定了一些可溶性形式的晶体结构，但对于重要的膜结合状态却知之甚少。我们采用定点自旋标记法来证明：1）膜联蛋白XII在生理条件下与双层膜结合时呈现出与晶体结构相似的三聚体构型；2）在双层膜上三聚体的组装非常迅速，发生在毫秒时间尺度上，而亚基交换则需要数小时；3）不同的膜联蛋白可以混合形成异源三聚体。这种快速组装和异源三聚体的形成对于膜联蛋白的细胞功能具有重要意义。
