Nakajima K, Hamanoue M, Takemoto N, Hattori T, Kato K, Kohsaka S
Department of Neurochemistry, National Institute of Neuroscience, Tokyo.
J Neurochem. 1994 Dec;63(6):2048-57. doi: 10.1046/j.1471-4159.1994.63062048.x.
Plasminogen (PGn) that we identified in microglial-conditioned medium has a neurotrophic factor-like effect on cultured neurons. We have also shown that PGn binds specifically to a protein with a molecular mass of 45 kDa in the neuronal plasma membrane. As a candidate PGn receptor-like molecule on the neuronal surface, this 45-kDa protein was purified from the plasma membrane of embryonic rat brain. Amino acid sequence analysis of polypeptides derived from the cleavage of the protein with cyanogen bromide and V8 protease revealed that the 45-kDa protein is identical to rat alpha-enolase. In fact, PGn was found to bind to purified rat alpha-enolase and also to a synthetic peptide (30 residues) that corresponds to the carboxyl terminal region of rat alpha-enolase. Physical properties of the 45-kDa protein, such as molecular mass, isoelectric point, and the ability to form dimers, are quite similar to those of alpha-enolase. The 45-kDa PGn-binding protein in the plasma membrane was also recognized by anti-rat alpha-enolase antibody, and pretreatment with alpha-enolase antibody markedly diminished the PGn-binding to the plasma membrane. In addition, immunocytochemical staining of the cultured cells under the nonpermeable condition showed that alpha-enolase is present on the cell surface of a certain population of neurons. These results suggest that alpha-enolase may function as a PGn-binding molecule on the neuronal cell surface.
我们在小胶质细胞条件培养基中鉴定出的纤溶酶原（PGn）对培养的神经元具有神经营养因子样作用。我们还表明，PGn与神经元质膜中一种分子量为45 kDa的蛋白质特异性结合。作为神经元表面候选的PGn受体样分子，这种45 kDa的蛋白质是从胚胎大鼠脑的质膜中纯化出来的。用溴化氰和V8蛋白酶切割该蛋白质产生的多肽的氨基酸序列分析表明，45 kDa的蛋白质与大鼠α-烯醇化酶相同。事实上，发现PGn与纯化的大鼠α-烯醇化酶以及与大鼠α-烯醇化酶羧基末端区域对应的合成肽（30个残基）结合。45 kDa蛋白质的物理性质，如分子量、等电点和形成二聚体的能力，与α-烯醇化酶非常相似。质膜中45 kDa的PGn结合蛋白也能被抗大鼠α-烯醇化酶抗体识别，用α-烯醇化酶抗体预处理可显著减少PGn与质膜的结合。此外，在非通透条件下对培养细胞进行免疫细胞化学染色显示，α-烯醇化酶存在于一定数量神经元的细胞表面。这些结果表明，α-烯醇化酶可能作为神经元细胞表面的PGn结合分子发挥作用。
