Allosterism in membrane binding: A common motif of the annexins?
Allosterism in membrane binding: A common motif of the annexins?
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DOI：
10.1021/bi050474g
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发表时间：
2005-08-16
期刊：
影响因子：
2.9
通讯作者：
Hinderliter, A
中科院分区：
文献类型：
--
作者：
Almeida, PFF;Sohma, H;Hinderliter, A
膜联蛋白是一个蛋白质家族，通常被描述为磷脂结合的Ca 2+依赖性。然而，膜联蛋白具有多种结合行为和构象状态，其中一些是脂质依赖性和Ca 2+非依赖性的。我们提出了一个模型，捕捉阳离子和磷脂结合行为的高度保守的核心膜联蛋白。膜联蛋白A4和A5的实验数据，其中有短的N-末端，在全球范围内建模，以获得保守的蛋白质核心的脂质结合亲和力是如何调制的理解。通过使用镧系元素Tb 3+作为Ca 2+类似物来实现结合行为的分析。结合等温线的实验确定的内在荧光的膜联蛋白A4和A5的Tb 3+在存在或不存在的膜的猝灭。在脂质存在下，膜联蛋白对阳离子的亲和力增加，结合等温线从双曲线变为弱S形。这种行为是由微观结合分配函数的等温线模拟。从双曲线到S形结合的变化发生，因为从膜联蛋白溶液状态到其膜缔合状态的变构转变。蛋白质与脂质双层的结合使得膜联蛋白与阳离子的结合具有协同性。两种膜联蛋白状态表示蛋白质对阳离子的两种亲和力，一种在膜不存在的情况下，另一种在膜存在的情况下。在这个模型的框架中，我们讨论膜结合以及在修改膜联蛋白阳离子结合亲和力的N-末端的影响，通过改变蛋白质的概率进行假设的两个状态的转变。
Annexins are a family of proteins generally described as Ca2+-dependent for phospholipid binding. Yet, annexins have a wide variety of binding behaviors and conformational states, some of which are lipid-dependent and Ca2+-independent. We present a model that captures the cation and phospholipid binding behavior of the highly conserved core of the annexins. Experimental data for annexins A4 and A5, which have short N-termini, were globally modeled to gain an understanding of how the lipid-binding affinity of the conserved protein core is modulated. Analysis of the binding behavior was achieved through use of the lanthanide Tb3+ as a Ca2+ analogue. Binding isotherms were determined experimentally from the quenching of the intrinsic fluorescence of annexins A4 and A5 by Tb3+ in the presence or absence of membranes. In the presence of lipid, the affinity of annexin for cation increases, and the binding isotherms change from hyperbolic to weakly sigmoidal. This behavior was modeled by isotherms derived from microscopic binding partition functions. The change from hyperbolic to sigmoidal binding occurs because of an allosteric transition from the annexin solution state to its membrane-associated state. Protein binding to lipid bilayers renders cation binding by annexins cooperative. The two annexin states denote two affinities of the protein for cation, one in the absence and another in the presence of membrane. In the framework of this model, we discuss membrane binding as well as the influence of the N-terminus in modifying the annexin cation-binding affinity by changing the probability of the protein to undergo the postulated two-state transition.