Srinivas S K, Srinivas R V, Anantharamaiah G M, Compans R W, Segrest J P
Department of Medicine, University of Alabama at Birmingham 35294.
J Biol Chem. 1993 Oct 25;268(30):22895-9.
Calmodulin (CaM), the major intracellular receptor for calcium, is involved in regulation of diverse cellular functions. Positively charged amphipathic helical segments have been identified as an important structural motif in the recognition of CaM by different CaM-activated enzymes and peptides. The carboxyl-terminal domain of the envelope glycoproteins of human and simian immunodeficiency viruses (HIV-1, HIV-2, and SIV) contain regions that can fold into amphipathic helical segments, which closely resemble the amphipathic segments found in CaM-activated enzymes. We show here that synthetic peptide analogs corresponding to the two putative amphipathic helical regions of HIV-1/WMJ gp160 bind to CaM with high affinity (Kd 31-41 nM) in the presence of calcium. They also bind CaM in the absence of calcium, although with much lower affinity. The peptides inhibit CaM-regulated activation of bovine brain phosphodiesterase in vitro. The peptides also inhibit mitogen-induced lymphocyte activation, a property shared by CaM antagonists. Purified HIV-1 gp160 binds to CaM, while gp120, which lacks the putative amphipathic helical segments, does not bind CaM. In HIV-infected cells, the putative CaM-binding regions of gp160 are located intracellularly and may therefore interact with the cytosolic CaM. We postulate that CaM binding by HIV envelope proteins is likely to exert diverse modulatory effects, and the mechanism for HIV-induced cytotoxicity may involve, in part, inhibition of CaM-regulated cellular functions.
钙调蛋白（CaM）是细胞内主要的钙受体，参与多种细胞功能的调节。带正电荷的两亲性螺旋片段已被确定为不同CaM激活酶和肽识别CaM的重要结构基序。人类和猿猴免疫缺陷病毒（HIV-1、HIV-2和SIV）包膜糖蛋白的羧基末端结构域包含可折叠成两亲性螺旋片段的区域，这些区域与CaM激活酶中发现的两亲性片段非常相似。我们在此表明，与HIV-1/WMJ gp160的两个假定两亲性螺旋区域相对应的合成肽类似物在钙存在的情况下以高亲和力（Kd 31 - 41 nM）与CaM结合。它们在没有钙的情况下也能结合CaM，尽管亲和力要低得多。这些肽在体外抑制CaM调节的牛脑磷酸二酯酶的激活。这些肽还抑制丝裂原诱导的淋巴细胞激活，这是CaM拮抗剂共有的特性。纯化的HIV-1 gp160与CaM结合，而缺乏假定两亲性螺旋片段的gp120则不与CaM结合。在HIV感染的细胞中，gp160假定的CaM结合区域位于细胞内，因此可能与胞质CaM相互作用。我们推测，HIV包膜蛋白与CaM的结合可能会产生多种调节作用，并且HIV诱导细胞毒性的机制可能部分涉及抑制CaM调节的细胞功能。
