Ernst J D, Hoye E, Blackwood R A, Jaye D
Department of Medicine, Rosalind Russell Arthritis Research Laboratory, San Francisco, California.
J Clin Invest. 1990 Apr;85(4):1065-71. doi: 10.1172/JCI114537.
Intracellular ionized calcium has been strongly implicated in mediating several responses of human neutrophils to stimulation. However, proteins that serve as effectors of these responses have not been well characterized. To identify proteins that might serve as mediators of the effects of Ca2+ in human neutrophils, we isolated proteins that bind to membrane phospholipids in a Ca2(+)-dependent manner. The most abundant of these, a protein of 33 kD, was readily purified to homogeneity, and was found to bind to phosphatidylserine vesicles in the presence of 2 microM ionized Ca2+. In addition, this purified protein promoted Ca2(+)-dependent aggregation of isolated specific granules from human neutrophils, indicating that it might mediate membrane-membrane contact during processes such as phagosome-lysosome fusion or degranulation. This protein was localized to the cytoplasm of unstimulated neutrophils and found to account for approximately 1% of the cytosol protein. Amino acid sequence of several peptides derived from the purified protein revealed that it is identical to lipocortin III, a recently described member of the annexin family that is scarce in other cells and tissues. The abundance of this protein, together with its Ca2(+)-dependent membrane effects, suggest that it mediates membrane-localized events in stimulated neutrophils, such as phagosome-lysosome fusion or degranulation.
细胞内游离钙在介导人类中性粒细胞对刺激的多种反应中发挥着重要作用。然而，作为这些反应效应器的蛋白质尚未得到充分表征。为了鉴定可能作为人类中性粒细胞中Ca2+效应介质的蛋白质，我们分离了以Ca2+依赖方式与膜磷脂结合的蛋白质。其中最丰富的一种是33 kD的蛋白质，很容易纯化至同质，并且发现在存在2 microM游离Ca2+的情况下与磷脂酰丝氨酸囊泡结合。此外，这种纯化的蛋白质促进了从人类中性粒细胞中分离出的特定颗粒的Ca2+依赖聚集，表明它可能在吞噬体 - 溶酶体融合或脱颗粒等过程中介导膜 - 膜接触。该蛋白质定位于未受刺激的中性粒细胞的细胞质中，约占胞质溶胶蛋白质的1%。从纯化蛋白质衍生的几种肽的氨基酸序列显示，它与脂皮质素III相同，脂皮质素III是膜联蛋白家族中最近描述的成员，在其他细胞和组织中含量稀少。这种蛋白质的丰度及其Ca2+依赖的膜效应表明，它介导了受刺激的中性粒细胞中的膜定位事件，如吞噬体 - 溶酶体融合或脱颗粒。
