The retinoblastoma protein (Rb) and its homologs p107 and p130 are critical regulators of gene expression during the cell cycle and are commonly inactivated in cancer. Rb proteins use their “pocket domain” to bind an LxCxE sequence motif in other proteins, many of which function with Rb proteins to co-regulate transcription. Here, we present binding data and crystal structures of the p107 pocket domain in complex with LxCxE peptides from the transcriptional co-repressor proteins HDAC1, ARID4A, and EID1. Our results explain why Rb and p107 have weaker affinity for cellular LxCxE proteins compared with the E7 protein from human papillomavirus, which has been used as the primary model for understanding LxCxE motif interactions. Our structural and mutagenesis data also identify and explain differences in Rb and p107 affinities for some LxCxE-containing sequences. Our study provides new insights into how Rb proteins bind their cell partners with varying affinity and specificity.

视网膜母细胞瘤蛋白 (Rb) 及其同源物 p107 和 p130 是细胞周期中基因表达的关键调节因子，并且通常在癌症中失活。Rb 蛋白利用其“口袋结构域”结合其他蛋白中的 LxCxE 序列基序，其中许多蛋白与 Rb 蛋白共同发挥作用，共同调节转录。在这里，我们展示了 p107 口袋结构域与来自转录共阻遏蛋白 HDAC1、ARID4A 和 EID1 的 LxCxE 肽复合物的结合数据和晶体结构。我们的结果解释了为什么与人乳头瘤病毒的 E7 蛋白相比，Rb 和 p107 对细胞 LxCxE 蛋白的亲和力较弱，而人乳头瘤病毒已被用作了解 LxCxE 基序相互作用的主要模型。我们的结构和诱变数据还识别并解释了一些包含 LxCxE 的序列的 Rb 和 p107 亲和力的差异。我们的研究为 Rb 蛋白如何以不同的亲和力和特异性结合其细胞伴侣提供了新的见解。