Ubiquitin Ligase Activity of Cul3-KLHL7 Protein Is Attenuated by Autosomal Dominant Retinitis Pigmentosa Causative Mutation
Ubiquitin Ligase Activity of Cul3-KLHL7 Protein Is Attenuated by Autosomal Dominant Retinitis Pigmentosa Causative Mutation
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DOI：
10.1074/jbc.m111.245126
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发表时间：
2011-09-23
影响因子：
4.8
通讯作者：
Chiba, Tomoki
中科院分区：
文献类型：
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作者：
Kigoshi, Yu;Tsuruta, Fuminori;Chiba, Tomoki
由泛素蛋白酶体系统 (UPS) 介导的底物特异性蛋白质降解对于细胞的正常功能至关重要。蛋白质被泛素连接酶 (E3) 特异性识别和泛素化，然后被蛋白酶体降解。 BTB 蛋白充当底物识别亚基，将其同源底物募集到基于 Cullin 3 的多亚基 E3 中。最近，据报道，BTB-Kelch 蛋白 KLHL7 的错义突变与常染色体显性视网膜色素变性（adRP）有关。然而，KLHL7 在 UPS 中的参与以及 adRP 致病突变的结果尚不清楚。在这项研究中，我们发现 KLHL7 形成二聚体，通过其 BTB 和 BACK 结构域与 Cul3 组装，并发挥 E3 活性。 Lys-48 连接但非 Lys-63 连接的多聚泛素链与 KLHL7 共定位，在蛋白酶体抑制时增加，表明 KLHL7 通过 UPS 介导蛋白质降解。 KLHL7 BACK 结构域中的 adRP 致病性错义突变仅减弱了 Cul3 相互作用，但不减弱二聚化。然而，将突变体作为异二聚体掺入 Cul3-KLHL7 复合物中会降低 E3 连接酶活性。总之，我们的结果表明，KLHL7 构成了基于 Cul3 的 E3，并且致病突变以显性失活方式抑制连接酶活性，这可能导致蛋白酶体降解的底物不适当的积累。
Substrate-specific protein degradation mediated by the ubiquitin proteasome system (UPS) is crucial for the proper function of the cell. Proteins are specifically recognized and ubiquitinated by the ubiquitin ligases (E3s) and are then degraded by the proteasome. BTB proteins act as the substrate recognition subunit that recruits their cognate substrates to the Cullin 3-based multisubunit E3s. Recently, it was reported that missense mutations in KLHL7, a BTB-Kelch protein, are related to autosomal dominant retinitis pigmentosa (adRP). However, the involvement of KLHL7 in the UPS and the outcome of the adRP causative mutations were unknown. In this study, we show that KLHL7 forms a dimer, assembles with Cul3 through its BTB and BACK domains, and exerts E3 activity. Lys-48-linked but not Lys-63-linked polyubiquitin chain co-localized with KLHL7, which increased upon proteasome inhibition suggesting that KLHL7 mediates protein degradation via UPS. An adRP-causative missense mutation in the BACK domain of KLHL7 attenuated only the Cul3 interaction but not dimerization. Nevertheless, the incorporation of the mutant as a heterodimer in the Cul3-KLHL7 complex diminished the E3 ligase activity. Together, our results suggest that KLHL7 constitutes a Cul3-based E3 and that the disease-causing mutation inhibits ligase activity in a dominant negative manner, which may lead to the inappropriate accumulation of the substrates targeted for proteasomal degradation.