CHIP is a U-box-dependent E3 ubiquitin ligase -: Identification of Hsc70 as a target for ubiquitylation
CHIP is a U-box-dependent E3 ubiquitin ligase -: Identification of Hsc70 as a target for ubiquitylation
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DOI：
10.1074/jbc.m101968200
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发表时间：
2001-11-16
影响因子：
4.8
通讯作者：
Patterson, C
中科院分区：
文献类型：
--
作者：
Jiang, JH;Ballinger, CA;Patterson, C
蛋白质的正确折叠（无论是新合成的还是因应激事件而受损）以高度调控的方式发生。 Hsc/Hsp70 等胞质伴侣受到以正向或负向方式调节折叠机制的辅因子的协助。 CHIP（Hsc70 相互作用蛋白的羧基末端）是一种与 Hsc70 相互作用的辅助因子，通常会减弱其最明确的功能。此外，CHIP 还可加速伴侣底物的泛素依赖性降解。使用重组蛋白的体外泛素化测定，我们证明 CHIP 具有内在的 E3 泛素连接酶活性并促进泛素化。该活性依赖于羧基末端 U 盒。 CHIP 在功能和物理上与应激反应性泛素结合酶家族 UBCH5 相互作用。令人惊讶的是，CHIP 泛素连接酶活性的主要目标是 Hsc70 本身。 CHIP 主要通过短的、非规范的多泛素链泛素化 Hsc70，但对该蛋白质的稳态水平或半衰期没有明显影响。这种效应可能会对 Hsc70 的陪伴活性或其将底物递送至蛋白酶体的能力产生迄今为止意想不到的后果。这些研究表明 CHIP 是一种真正的泛素连接酶，并表明含有 U-box 的蛋白质可能包含一个新的 E3 家族。
Proper folding of proteins (either newly synthesized or damaged in response to a stressful event) occurs in a highly regulated fashion. Cytosolic chaperones such as Hsc/Hsp70 are assisted by cofactors that modulate the folding machinery in a positive or negative manner. CHIP (carboxyl terminus of Hsc70-interacting protein) is such a cofactor that interacts with Hsc70 and, in general, attenuates its most well characterized functions. In addition, CHIP accelerates ubiquitin-dependent degradation of chaperone substrates. Using an in vitro ubiquitylation assay with recombinant proteins, we demonstrate that CHIP possesses intrinsic E3 ubiquitin ligase activity an promotes ubiquitylation. This activity is dependent on the carboxyl-terminal U-box. CHIP interacts functionally and physically with the stress-responsive ubiquitin-conjugating enzyme family UBCH5. Surprisingly, a major target of the ubiquitin ligase activity of CHIP is Hsc70 itself. CHIP ubiquitylates Hsc70, primarily with short, noncanonical multiubiquitin chains but has no appreciable effect on steady-state levels or half-life of this protein. This effect may have heretofore unanticipated consequences with regard to the chaperoning activities of Hsc70 or its ability to deliver substrates to the proteasome. These studies demonstrate that CHIP is a bona fide ubiquitin ligase and indicate that U-box-containing proteins may comprise a new family of E3s.