Dove Katja K, Olszewski Jennifer L, Martino Luigi, Duda David M, Wu Xiaoli S, Miller Darcie J, Reiter Katherine H, Rittinger Katrin, Schulman Brenda A, Klevit Rachel E
Department of Biochemistry, University of Washington, 1705 Northeast Pacific Street, Seattle, WA 98195, USA.
Department of Structural Biology, St. Jude Children's Research Hospital, 262 Danny Thomas Place, Memphis, TN 38105, USA.
Structure. 2017 Jun 6;25(6):890-900.e5. doi: 10.1016/j.str.2017.04.013. Epub 2017 May 25.
RING-between-RING (RBR) E3s contain RING1 domains that are structurally similar yet mechanistically distinct from canonical RING domains. Both types of E3 bind E2∼ubiquitin (E2∼Ub) via their RINGs but canonical RING E3s promote closed E2∼Ub conformations required for direct Ub transfer from the E2 to substrate, while RBR RING1s promote open E2∼Ub to favor Ub transfer to the E3 active site. This different RING/E2∼Ub conformation determines its direct target, which for canonical RING E3s is typically a substrate or substrate-linked Ub, but is the E3 active-site cysteine in the case of RBR-type E3s. Here we show that a short extension of HHARI RING1, namely Zn-loop II, not present in any RING E3s, acts as a steric wedge to disrupt closed E2∼Ub, providing a structural explanation for the distinctive RING1-dependent conformational restriction mechanism utilized by RBR E3s.
环状结构间环状结构（RBR）E3泛素连接酶包含RING1结构域，其在结构上与典型的RING结构域相似，但在机制上有所不同。这两种类型的E3泛素连接酶都通过其RING结构域结合E2泛素（E2Ub），但典型的RING E3泛素连接酶促进E2Ub形成封闭构象，这是泛素从E2直接转移到底物所必需的，而RBR的RING1结构域促进E2Ub形成开放构象，有利于泛素转移到E3活性位点。这种不同的RING/E2Ub构象决定了其直接靶点，对于典型的RING E3泛素连接酶来说，通常是底物或与底物相连的泛素，但对于RBR型E3泛素连接酶来说，靶点是E3活性位点的半胱氨酸。在这里，我们表明，HHARI的RING1结构域有一个短的延伸，即锌环II，这在任何RING E3泛素连接酶中都不存在，它作为一个空间楔来破坏封闭的E2Ub，为RBR E3泛素连接酶独特的依赖RING1的构象限制机制提供了结构解释。
