Molecular And Biochemical Characterization Of GTP-bindin

蛋白质泛素化在许多重要的细胞过程中起着关键作用。泛素化需要E1泛素激活酶、E2泛素结合酶，通常还需要底物特异性的E3泛素蛋白连接酶。在一类E3泛素连接酶中，催化结构域包含一个锌结合的环指基序。ARD1(ADP-核糖化因子结构域蛋白1)最初是在本实验室克隆的，它在N-末端含有一个环指结构域，两个预测的B-盒，在C末端紧接ADP-核糖化因子结构域之前的一个卷曲卷曲蛋白相互作用基序，属于TRIM(三部分基序)或RBCC(环，B-盒，卷曲-线圈)家族。包含B-盒和卷曲螺旋基序的区域作为ARD1的ADP-核糖化因子结构域的GTP酶激活蛋白。我们在这里报道了全长ARD1或环指结构域(残基1-110)在哺乳动物E1和E2酶(UbcH6或UbcH5a、-5b或-5c)、ATP和泛素存在的情况下在体外产生多泛素化蛋白。环序列内的环区或点突变的缺失使ARD1E3连接酶活性丧失。所有数据都与ARD1作为E3泛素连接酶在细胞中的潜在功能一致。

Protein ubiquitinylation plays a key role in many important cellular processes. Ubiquitinylation requires the E1 ubiquitin-activating enzyme, an E2 ubiquitin-conjugating enzyme, and, frequently, a substrate-specific E3 ubiquitin-protein ligase. In one class of E3 ubiquitin ligases, the catalytic domain contains a zinc-binding RING finger motif. ARD1 (ADP-ribosylation factor domain protein 1), initially cloned in this laboratory, contains a RING finger domain in the N-terminal region, two predicted B-Boxes, and a coiled-coil protein interaction motif immediately preceding an ADP-ribosylaiton factor domain at the C terminus, belongs to the TRIM (Tripartite motif) or RBCC (RING, B-Box, coiled-coil) family. The region containing the B-Boxes and the coiled-coil motif acts as a GTPase-activating protein for the ADP-ribosylation factor domain of ARD1. We report here that full-length ARD1 or the RING finger domain (residues 1-110) produced polyubiquitinylated proteins in vitro in the presence of mammalian E1, and E2 enzyme (UbcH6 or UbcH5a, -5b, or -5c), ATP, and ubiquitin. Deletion of the RING region or point mutations within the RING sequence abolished ARD1 E3 ligase activity. All data are consistent with a potential function for ARD1 as an E3 ubiquitin ligase in cells.