Memorial Sloan-Kettering Cancer Center, Howard Hughes Medical Institute and the Structural Biology Program, New York, NY, USA.
EMBO J. 2013 Apr 3;32(7):926-37. doi: 10.1038/emboj.2013.41. Epub 2013 Mar 12.
Cytoplasmic dilysine motifs on transmembrane proteins are captured by coatomer α-COP and β'-COP subunits and packaged into COPI-coated vesicles for Golgi-to-ER retrieval. Numerous ER/Golgi proteins contain K(x)Kxx motifs, but the rules for their recognition are unclear. We present crystal structures of α-COP and β'-COP bound to a series of naturally occurring retrieval motifs-encompassing KKxx, KxKxx and non-canonical RKxx and viral KxHxx sequences. Binding experiments show that α-COP and β'-COP have generally the same specificity for KKxx and KxKxx, but only β'-COP recognizes the RKxx signal. Dilysine motif recognition involves lysine side-chain interactions with two acidic patches. Surprisingly, however, KKxx and KxKxx motifs bind differently, with their lysine residues transposed at the binding patches. We derive rules for retrieval motif recognition from key structural features: the reversed binding modes, the recognition of the C-terminal carboxylate group which enforces lysine positional context, and the tolerance of the acidic patches for non-lysine residues.
跨膜蛋白的细胞质双赖氨酰基模体被衣被蛋白α-COP 和 β'-COP 亚基捕获，并包装到 COPI 被膜小泡中，用于高尔基体到内质网的回收。许多内质网/高尔基体蛋白含有 K(x)Kxx 模体，但它们的识别规则尚不清楚。我们展示了α-COP 和 β'-COP 与一系列天然存在的回收模体结合的晶体结构，包括 KKxx、KxKxx 和非典型的 RKxx 和病毒 KxHxx 序列。结合实验表明，α-COP 和 β'-COP 对 KKxx 和 KxKxx 具有大致相同的特异性，但只有 β'-COP 识别 RKxx 信号。双赖氨酰基模体识别涉及赖氨酸侧链与两个酸性斑之间的相互作用。然而，令人惊讶的是，KKxx 和 KxKxx 模体的结合方式不同，其赖氨酸残基在结合斑处置换。我们从关键结构特征中得出了回收模体识别的规则：反向结合模式、对强制赖氨酸位置上下文的 C 末端羧基基团的识别以及酸性斑对非赖氨酸残基的容忍度。
