Illien Françoise, Piao Hong-Rong, Coué Marine, di Marco Chiara, Ayala-Sanmartin Jesus
Laboratoire des Biomolecules, Groupe N J Conte, Paris, France.
Biochim Biophys Acta. 2012 Nov;1818(11):2892-900. doi: 10.1016/j.bbamem.2012.07.012. Epub 2012 Jul 25.
Annexin A2 (AnxA2) is a phospholipid binding protein that has been implicated in many membrane-related cellular functions. AnxA2 is able to bind different acidic phospholipids such as phosphatidylserine (PS) and phosphatidylinositol-4,5-bisphosphate (PI2P). This binding is mediated by Ca(2+)-dependent and Ca(2+)-independent mechanisms. The specific functions of annexin A2 related to these two phospholipids and the molecular mechanisms involved in their interaction remain obscure. Herein we studied the influence of lipid composition on the Ca(2+)-dependency of AnxA2-mediated membrane bridging and on membrane fluidity. Membrane models of ten different lipid compositions and detergent-resistant membranes from two cellular sources were investigated. The results show that the AnxA2-mediated membrane bridging requires 3 to 50 times less calcium for PS-membranes than for PI2P-membranes. Membrane fluidity was measured by the ratiometric fluorescence parameter generalized polarization method with two fluorescent probes. Compared to controls containing low phospholipid ligand, AnxA2 was found to reduce the membrane fluidity of PI2P-membranes twice as much as the PS-membranes in the presence of calcium. On the contrary, at mild acidic pH in the absence of calcium AnxA2 reduces the fluidity of the PS-membranes more than the PI2P-membranes. The presence of cholesterol on the bilayer reduced the AnxA2 capacity to reduce membrane fluidity. The presented data shed light on the specific roles of PI2P, PS and cholesterol present on membranes related to the action of annexin A2 as a membrane bridging molecule during exocytosis and endocytosis events and as a plasma membrane domain phospholipid packing regulator.
膜联蛋白A2（AnxA2）是一种磷脂结合蛋白，与许多膜相关的细胞功能有关。AnxA2能够结合不同的酸性磷脂，如磷脂酰丝氨酸（PS）和磷脂酰肌醇-4,5-二磷酸（PI2P）。这种结合由钙依赖性和非钙依赖性机制介导。与这两种磷脂相关的膜联蛋白A2的具体功能及其相互作用的分子机制仍不清楚。在此，我们研究了脂质组成对AnxA2介导的膜桥接的钙依赖性和膜流动性的影响。研究了十种不同脂质组成的膜模型以及来自两种细胞来源的抗去污剂膜。结果表明，AnxA2介导的膜桥接对于PS膜所需的钙比PI2P膜少3至50倍。通过使用两种荧光探针的比率荧光参数广义极化方法测量膜流动性。与含有低磷脂配体的对照相比，发现在有钙的情况下，AnxA2使PI2P膜的膜流动性降低的程度是PS膜的两倍。相反，在无钙的轻度酸性pH条件下，AnxA2使PS膜的流动性降低的程度比PI2P膜更大。双层膜上胆固醇的存在降低了AnxA2降低膜流动性的能力。所呈现的数据揭示了膜上存在的PI2P、PS和胆固醇在膜联蛋白A2作为胞吐作用和胞吞作用过程中的膜桥接分子以及作为质膜结构域磷脂堆积调节剂的作用中的具体作用。
