Hu Nien-Jen, Bradshaw Jeremy, Lauter Hans, Buckingham Julia, Solito Egle, Hofmann Andreas
Institute of Structural and Molecular Biology, School of Biological Sciences, The University of Edinburgh, Edinburgh EH9 3JR, United Kingdom.
Biophys J. 2008 Mar 1;94(5):1773-81. doi: 10.1529/biophysj.107.119685. Epub 2007 Nov 9.
Annexins constitute a family of calcium-dependent membrane-binding proteins and can be classified into two groups, depending on the length of the N-terminal domain unique for each individual annexin. The N-terminal domain of annexin A1 can adopt an alpha-helical conformation and has been implicated in mediating the membrane aggregation behavior of this protein. Although the calcium-independent interaction of the annexin A1 N-terminal domain has been known for some time, there was no structural information about the membrane interaction of this secondary membrane-binding site of annexin A1. This study used circular dichroism spectroscopy to show that a rat annexin A1 N-terminal peptide possesses random coil structure in aqueous buffer but an alpha-helical structure in the presence of small unilamellar vesicles. The binding of peptides to membranes was confirmed by surface pressure (Langmuir film balance) measurements using phosphatidylcholine/phosphatidylserine monolayers, which show a significant increase after injection of rat annexin A1 N-terminal peptides. Lamellar neutron diffraction with human and rat annexin A1 N-terminal peptides reveals an intercalation of the helical peptides with the phospholipid bilayer, with the helix axis lying parallel to the surface of membrane. Our findings confirm that phospholipid membranes assist the folding of the N-terminal peptides into alpha-helical structures and that this conformation enables favorable direct interactions with the membrane. The results are consistent with the hypothesis that the N-terminal domain of annexin A1 can serve as a secondary membrane binding site in the process of membrane aggregation by providing a peripheral membrane anchor.
膜联蛋白是一类钙依赖性膜结合蛋白家族，根据每个膜联蛋白独特的N端结构域长度可分为两组。膜联蛋白A1的N端结构域可呈α螺旋构象，并参与介导该蛋白的膜聚集行为。尽管膜联蛋白A1 N端结构域的钙非依赖性相互作用已为人所知一段时间，但关于膜联蛋白A1这个二级膜结合位点的膜相互作用尚无结构信息。本研究使用圆二色光谱表明，大鼠膜联蛋白A1 N端肽在水性缓冲液中具有无规卷曲结构，但在存在小单层囊泡时具有α螺旋结构。使用磷脂酰胆碱/磷脂酰丝氨酸单层通过表面压力（朗缪尔膜天平）测量证实了肽与膜的结合，在注射大鼠膜联蛋白A1 N端肽后显示出显著增加。对人和大鼠膜联蛋白A1 N端肽进行的层状中子衍射揭示了螺旋肽与磷脂双层的插入，螺旋轴与膜表面平行。我们的研究结果证实，磷脂膜有助于N端肽折叠成α螺旋结构，并且这种构象能够与膜形成有利的直接相互作用。这些结果与以下假设一致，即膜联蛋白A1的N端结构域可通过提供外周膜锚定在膜聚集过程中作为二级膜结合位点。
