HIGHLY SEQUENTIAL BINDING OF PROTEIN-KINASE-C AND RELATED PROTEINS TO MEMBRANES
HIGHLY SEQUENTIAL BINDING OF PROTEIN-KINASE-C AND RELATED PROTEINS TO MEMBRANES
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DOI：
10.1021/bi00246a014
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发表时间：
1991-08-13
期刊：
影响因子：
2.9
通讯作者：
NELSESTUEN, GL
中科院分区：
文献类型：
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作者：
BAZZI, MD;NELSESTUEN, GL
蛋白激酶C属于一类同时与钙和磷脂相互作用的蛋白质。这一类的其他成员包括从牛脑中分离的两种蛋白质(M(R)64K和32K)。这些蛋白质与膜的结合表现出极不寻常的性质，不符合简单的平衡。蛋白质-磷脂结合强度随钙离子的变化呈明显的正常曲线，协同作用程度较低。结合速度很快，很快就能适应钙离子浓度的变化。钙很容易从蛋白质-磷脂复合体中交换出来。然而，在不同的钙浓度下，膜结合蛋白与溶液中的游离蛋白并不处于快速平衡状态，解离的半衰期超过24小时。在不同的钙浓度下，膜结合蛋白的饱和程度不同。结合蛋白的量几乎完全由钙的浓度决定，而几乎不受游离蛋白浓度的影响。这些性质表明，蛋白质-磷脂结合涉及一系列步骤，每个步骤在完成时都是不可逆的。这些结合特性与蛋白质和磷脂之间的高亲和力、与钙的高协同性(N大于或等于10)、酸性磷脂的聚集以及与膜上蛋白质密度的负协同性是一致的。PKC-膜相互作用的完全滴定的一个主要明显问题是对细胞内钙的需求超过细胞内水平。然而，高度连续的结合过程表明，在生理水平上，膜上的一些蛋白质结合部位会被钙饱和。序列结合的不同寻常的性质可能为钙调节提供其他重要的机制。
Protein kinase C belongs to a class of proteins that displays simultaneous interaction with calcium and phospholipids. Other members of this class include two proteins (M(r) 64K and 32K) isolated from bovine brain. The association of these proteins with membranes exhibited highly unusual properties that were not consistent with a simple equilibrium. Titration of protein-phospholipid binding as a function of calcium showed an apparently normal curve with a low degree of cooperativity. The binding was rapid and quickly adjusted to changes in the calcium concentration. Calcium was readily exchanged from the protein-phospholipid complex. However, at each calcium concentration, membrane-bound protein was not in rapid equilibrium with free protein in solution; the half-time for dissociation exceeded 24 h. Titration of phospholipid vesicles with proteins showed different saturation levels of bound protein at different calcium concentrations. The amount of protein bound was almost entirely determined by the concentration of calcium and was virtually unaffected by the free protein concentration. These properties suggested that protein-phospholipid binding involved a sequence of steps that were each irreversible upon completion. These binding properties were consistent with high-affinity interaction between protein and phospholipid, high cooperativity with respect to calcium (N greater-than-or-equal-to 10), clustering of acidic phospholipids, and negative cooperativity with respect to protein density on the membrane. A major apparent problem with the complete titration of PKC-membrane interaction was a requirement for calcium in excess of intracellular levels. However, a highly sequential binding process showed that a number of protein-binding sites on the membrane would be saturated with calcium at physiological levels. The unusual properties of sequential binding may provide other important mechanisms for calcium regulation.