The BRCA1/BARD1 heterodimer assembles polyubiquitin chains through an unconventional linkage involving lysine residue K6 of ubiquitin
The BRCA1/BARD1 heterodimer assembles polyubiquitin chains through an unconventional linkage involving lysine residue K6 of ubiquitin
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DOI：
10.1074/jbc.c300249200
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发表时间：
2003-09-12
影响因子：
4.8
通讯作者：
Baer, R
中科院分区：
文献类型：
--
作者：
Wu-Baer, F;Lagrazon, K;Baer, R
BRCA1 肿瘤抑制因子与 BARD1 蛋白形成异二聚体，所得复合物充当 E3 泛素连接酶，催化多泛素链的合成。理论上，多泛素化可以通过在泛素的七个赖氨酸残基中的任何一个处形成异肽键来发生。多聚泛素链的异肽连接是其细胞功能的一个特别重要的决定因素，因此 K48 连接的链通常以蛋白酶体降解的蛋白质为目标，而 K63 链在各种信号传导途径中发挥非蛋白水解作用。为了确定 BRCA1/BARD1 依赖性多泛素化形成的异肽键，我们纯化了全长异二聚体复合物，并将其键特异性与 E6-AP 的键特异性进行比较，E6-AP 是一种已知可诱导其细胞底物蛋白水解的 E3 连接酶。通过全面的突变分析，我们发现 E6-AP 催化 K48 连接的多聚泛素链的合成。然而，相比之下，BRCA1/BARD1 异二聚体主要通过涉及赖氨酸残基 K6 的非常规连接来指导泛素聚合。尽管 BRCA1/BARD1 的异源底物尚不清楚，但 BRCA1 自动泛素化主要通过与 K6 连接的聚合物缀合而发生。 BRCA1/BARD1 形成 K6 连接的多聚泛素链的能力表明，它可能赋予其天然酶底物独特的细胞特性。
The BRCA1 tumor suppressor forms a heterodimer with the BARD1 protein, and the resulting complex functions as an E3 ubiquitin ligase that catalyzes the synthesis of polyubiquitin chains. In theory, polyubiquitination can occur by isopeptide bond formation at any of the seven lysine residues of ubiquitin. The isopeptide linkage of a polyubiquitin chain is a particularly important determinant of its cellular function, such that K48-linked chains commonly target proteins for proteasomal degradation, while K63 chains serve non-proteolytic roles in various signaling pathways. To determine the isopeptide linkage formed by BRCA1/BARD1-dependent polyubiquitination, we purified a full-length heterodimeric complex and compared its linkage specificity with that of E6-AP, an E3 ligase known to induce proteolysis of its cellular substrates. Using a comprehensive mutation analysis, we found that E6-AP catalyzes the synthesis of K48-linked polyubiquitin chains. In contrast, however, the BRCA1/BARD1 heterodimer directs polymerization of ubiquitin primarily through an unconventional linkage involving lysine residue K6. Although heterologous substrates of BRCA1/BARD1 are not known, BRCA1 autoubiquitination occurs principally by conjugation with K6-linked polymers. The ability of BRCA1/BARD1 to form K6-linked polyubiquitin chains suggests that it may impart unique cellular properties to its natural enzymatic substrates.