Bitto E, Li M, Tikhonov A M, Schlossman M L, Cho W
Departments of Chemistry (M/C 111) and Physics (M/C 273), University of Illinois at Chicago, 845 West Taylor Street, Chicago, Illinois 60607-7061, USA.
Biochemistry. 2000 Nov 7;39(44):13469-77. doi: 10.1021/bi001275u.
It has been proposed that annexin I has two separate interaction sites that are involved in membrane binding and aggregation, respectively. To better understand the mechanism of annexin I-mediated membrane aggregation, we investigated the properties of the inducible secondary interaction site implicated in membrane aggregation. X-ray specular reflectivity measurements showed that the thickness of annexin I layer bound to the phospholipid monolayer was 31 +/- 2 A, indicating that annexin I binds membranes as a protein monomer or monolayer. Surface plasmon resonance measurements of annexin I, V, and mutants, which allowed evaluation of membrane aggregation activity of annexin I separately from its membrane binding, revealed direct correlation between the relative membrane aggregation activity and the relative affinity of the secondary interaction site for the secondary membrane. The secondary binding was driven primarily by hydrophobic interactions, unlike calcium-mediated electrostatic primary membrane binding. Chemical cross-linking of membrane-bound annexin I showed that a significant degree of lateral association of annexin I molecules precedes its membrane aggregation. Taken together, these results support a hypothetical model of annexin I-mediated membrane aggregation, in which a laterally aggregated monolayer of membrane-bound annexin I directly interacts with a secondary membrane via its induced hydrophobic interaction site.
有人提出，膜联蛋白I有两个分别参与膜结合和聚集的独立相互作用位点。为了更好地理解膜联蛋白I介导的膜聚集机制，我们研究了与膜聚集有关的可诱导二级相互作用位点的特性。X射线镜面反射率测量表明，与磷脂单层结合的膜联蛋白I层的厚度为31±2埃，这表明膜联蛋白I以蛋白质单体或单层形式结合膜。对膜联蛋白I、V及其突变体的表面等离子体共振测量，使得能够独立于其膜结合来评估膜联蛋白I的膜聚集活性，结果揭示了相对膜聚集活性与二级相互作用位点对二级膜的相对亲和力之间的直接相关性。与钙介导的静电一级膜结合不同，二级结合主要由疏水相互作用驱动。对膜结合的膜联蛋白I进行化学交联表明，膜联蛋白I分子的显著程度的侧向缔合先于其膜聚集。综上所述，这些结果支持了膜联蛋白I介导的膜聚集的假设模型，其中膜结合的膜联蛋白I的侧向聚集单层通过其诱导的疏水相互作用位点直接与二级膜相互作用。
