Trivalent Arsenicals: Probes of Mechanism and Specificity inReactions of Ubiquitin-Protein Ligation

三价砷试剂与蛋白质特异性相互作用 带有连位巯基，形成非常稳定的环状 二硫代亚砷酸盐配合物。 这种复合物是无活性的，如果 巯基是关键的催化或调节元件。 泛素（Ub）是一种高度保守的小分子多肽， 与其他细胞蛋白质的连接可以产生蛋白质 降解 在某些情况下，Ub连接也可以用于 调节蛋白质功能。 三价砷被发现 抑制参与Ub蛋白连接的两种酶。之一 Ub载体蛋白（E2- 230 K）直接催化Ub 与蛋白质结合。 另一种是氨酰-tRNA蛋白 转移酶 催化的氨基末端酰基化反应 转移酶使蛋白质成为Ub连接的底物。 的 建议的研究解决机制和结构 这些酶的抑制三价的影响 砷剂 这些实验将揭示抑制是否 实际上是由砷剂与邻位 巯基，也将解决如何这个结构元素， 如果存在的话，其在催化和/或调节中起作用。 这 研究涉及催化机制的基本问题 和特异性，也可能导致 开发更好、更特异的抑制剂。

Trivalent arsenical reagents interact specificially with proteins bearing vicinal sulfhydryl groups, forming very stable cyclic dithioarsenite complexes. Such complexes are inactive if the sulfhydryl groups are critical catalytic or regulatory elements. Ubiquitin (Ub) is a small and highly-conserved polypeptide whose ligation to other cellular proteins can bring about protein degradation. In some cases, Ub ligation may also serve to regulate protein function. Trivalent arsenicals have been found to inhibit two enzymes involved in Ub protein ligation. One of these, a Ub carrier protein (E2-230K), directly catalyzes Ub conjugation to proteins. The other is an aminoacyl-tRNA protein transferase. Amino-terminal arginylation catalyzed by the transferase renders proteins substrates for Ub ligation. The proposed research addresses the mechanistic and structural implications of inhibition of these enzymes by trivalent arsenicals. The experiments will reveal whether inhibition is indeed mediated by interaction of arsenicals with vicinal sulfhydryls, and will also address how this structural element, if present, functions in catalysis and/or regulation. This research addresses basic issues concerning catalytic mechanism and specificity in Ub-protein ligation, and may also lead to development of better and more specific inhibitors.