Johnstone S A, Hubaishy I, Waisman D M
Department of Medical Biochemistry, University of Calgary, Alberta, Canada.
J Biol Chem. 1992 Dec 25;267(36):25976-81.
Annexin II tetramer (A-IIt) is a member of the annexin family of Ca2+ and phospholipid-binding proteins. The ability of this protein to aggregate both phospholipid vesicles and chromaffin granules has suggested a role for the protein in membrane trafficking events such as exocytosis. A-IIt is also a major intracellular substrate of both pp60src and protein kinase C; however, the effect of phosphorylation on the activity of this protein is unknown. In the current report we have examined the effect of phosphorylation on the lipid vesicle aggregation activity of the protein. Protein kinase C catalyzed the incorporation of 2.1 +/- 0.8 mol of phosphate/mol of A-IIt. Phosphorylation of A-IIt caused a dramatic decrease in the rate and extent of lipid vesicle aggregation without significantly effecting Ca(2+)-dependent lipid binding by the phosphorylated protein. Phosphorylation of A-IIt increased the A50%(Ca2+) of lipid vesicle aggregation from 0.18 microM to 0.65 mM. Activation of A-IIt phosphorylation, concomitant with activation of lipid vesicle aggregation, inhibited both the rate and extent of lipid vesicle aggregation but did not cause disassembly of the aggregated lipid vesicles. These results suggest that protein kinase C-dependent phosphorylation of A-IIt blocks the ability of the protein to aggregate phospholipid vesicles without affecting the lipid vesicle binding properties of the protein.
膜联蛋白 II 四聚体（A-IIt）是膜联蛋白家族中一种能结合钙离子和磷脂的蛋白质。该蛋白可使磷脂囊泡和嗜铬颗粒聚集，这表明它在诸如胞吐作用等膜运输过程中发挥作用。A-IIt 也是 pp60src 和蛋白激酶 C 的主要细胞内底物；然而，磷酸化对该蛋白活性的影响尚不清楚。在本报告中，我们研究了磷酸化对该蛋白脂质囊泡聚集活性的影响。蛋白激酶 C 催化每摩尔 A-IIt 掺入 2.1±0.8 摩尔磷酸。A-IIt 的磷酸化导致脂质囊泡聚集的速率和程度显著降低，而对磷酸化蛋白的钙离子依赖性脂质结合没有明显影响。A-IIt 的磷酸化使脂质囊泡聚集的 A50%（Ca2+）从 0.18μM 增加到 0.65 mM。A-IIt 磷酸化的激活与脂质囊泡聚集的激活同时发生，抑制了脂质囊泡聚集的速率和程度，但并未导致聚集的脂质囊泡解体。这些结果表明，蛋白激酶 C 依赖性的 A-IIt 磷酸化阻断了该蛋白聚集磷脂囊泡 的能力，而不影响该蛋白的脂质囊泡结合特性。
