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A novel calcium-independent peripheral membrane-bound form of annexin B12

机译：Annexin B12的一种新型的钙独立的外周膜结合形式

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摘要

Annexins are soluble proteins that can interact with membranes in a Ca2+-dependent manner. Recent studies have shown that they can also undergo Ca2+-independent membrane interactions that are modulated by pH and phospholipid composition. Here, we investigated the structural changes that occurred during Ca2+-independent interaction of annexin B12 with phospholipid vesicles as a function of pH. Electron paramagnetic resonance analysis of a helical hairpin encompassing the D and E helices in the second repeat of the protein showed that this region refolded and formed a continuous amphipathic a helix following Ca2+-independent binding to membranes at mildly acidic pH. At pH 4.0, this helix assumed a transmembrane topography, but at pH similar to 5.0-5.5, it was peripheral and approximately parallel to the membrane. The peripheral form was reversibly converted into the transmembrane form by lowering the pH and vice versa. Furthermore, analysis of vesicles incubated with annexin B12 using freeze-fracture electron microscopy methods showed classical intramembrane particles at pH 4.0 but none at pH 5.3. Together, these data raise the possibility that the peripheral-bound form of annexin B12 could act as a kinetic intermediate in the formation of the transmembrane form of the protein.
机译：膜联蛋白是可与Ca 2+依赖的方式与膜相互作用的可溶性蛋白。最近的研究表明，它们还可以进行不依赖Ca2 +的膜相互作用，该相互作用受pH和磷脂成分的调节。在这里，我们调查了膜联蛋白B12与磷脂囊泡的Ca2 +依赖性相互作用过程中发生的结构变化，这些变化是pH的函数。在蛋白质的第二个重复序列中包含D和E螺旋的螺旋发夹的电子顺磁共振分析表明，该区域重新折叠并在中等酸性pH下与Ca2 +无关地与膜结合后形成连续的两亲性螺旋。在pH 4.0时，该螺旋呈跨膜形貌，但在pH接近5.0-5.5时，它是外围的并且近似平行于膜。通过降低pH将外围形式可逆地转化为跨膜形式，反之亦然。此外，使用冷冻-断裂电子显微镜法分析与膜联蛋白B12一起温育的囊泡显示在pH 4.0下经典的膜内颗粒但在pH 5.3下没有。总之，这些数据增加了膜联蛋白B12的外周结合形式可以在蛋白质的跨膜形式形成中充当动力学中间体的可能性。

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