Phosphoinositides are a family of minority acidic phospholipids in cell membranes. Their principal role is instructional: they interact with proteins. Each cellular membrane compartment uses a characteristic species of phosphoinositide. This signature phosphoinositide attracts a specific complement of functionally important, loosely attached peripheral proteins to that membrane. For example, the phosphatidylinositol 4,5-bisphosphate (PIP2) of the plasma membrane attracts phospholipase C, protein kinase C, proteins involved in membrane budding and fusion, proteins regulating the actin cytoskeleton, and others. Phosphoinositides also regulate the activity level of the integral membrane proteins. Many ion channels of the plasma membrane need the plasma-membrane-specific PIP2 to function. Their activity decreases when the abundance of this lipid falls, as for example after activation of phospholipase C. This behaviour is illustrated by the suppression of KCNQ K+ channel current by activation of M1 muscarinic receptors; KCNQ channels require PIP2 for their activity. In summary, phosphoinositides contribute to the selection of peripheral proteins for each membrane and regulate the activity of the integral proteins.
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机译:磷酸肌醇是细胞膜中少数酸性磷脂的家族。它们的主要作用是指导性的:它们与蛋白质相互作用。每个细胞膜隔室使用特征性的磷酸肌醇。这种标志性的磷酸肌醇将功能上重要的,松散附着的外周蛋白吸引到该膜上。例如,质膜的磷脂酰肌醇4,5-二磷酸(PIP2)吸引磷脂酶C,蛋白激酶C,参与膜芽和融合的蛋白,调节肌动蛋白细胞骨架的蛋白等。磷酸肌醇还调节完整膜蛋白的活性水平。质膜的许多离子通道需要质膜特定的PIP2才能发挥作用。当这种脂质的丰度下降时,例如在磷脂酶C活化后,它们的活性下降。这种现象可以通过激活M1毒蕈碱受体来抑制KCNQ K + sup>通道电流来说明。 KCNQ频道需要PIP2才能进行活动。总之,磷酸肌醇有助于每个膜的外周蛋白的选择并调节整合蛋白的活性。
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