Rab23 is a member of the Rab family of small GTPases. It plays crucial roles in Hedgehog signaling, ciliary transport, and embryonic development. As a small GTPase, Rab23 cycles between the GDP-bound inactivated state and the GTP-bound activated state. Mutations in Rab23 are directly implicated in Carpenter syndrome, a development disorder characterized by deformed skulls, abnormal fingers or toes, and intellectual disabilities. Several clinical point mutations, for example, M12K, C85R, and Y79del, have been found to occur within the GTPase domain. However, the mechanisms of activation of Rab23 and pathogenesis of its clinical mutants are still unclear with limited structural information. So far, there are only two reported crystal structures of mouse Rab23 in complex with GDP. Here, we determined high-resolution crystal structures of human Rab23 and the human Rab23 Y79del clinical mutant, in complex with GDP and GMPPNP, a nonhydrolysable GTP analog, respectively. Supported by in vitro biochemical and functional analyses, we demonstrated that the Y79 deletion mutant exhibited structural distortions in the switch II region relative to that of the WT. The structural changes potentially disrupted the binding of Rab23 Y79del to its interacting partners, thus leading to a loss-of-function and the development of Carpenter syndrome.

中文翻译：

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Carpenter 综合征中 Rab23 激活和功能丧失突变的结构基础


Rab23 是小 GTP 酶 Rab 家族的成员。它在 Hedgehog 信号传导、纤毛运输和胚胎发育中起着至关重要的作用。作为一种小 GTP 酶，Rab23 在 GDP 结合的失活状态和 GTP 结合的激活状态之间循环。Rab23 的突变与 Carpenter 综合征直接相关，Carpenter 综合征是一种以颅骨变形、手指或脚趾异常和智力障碍为特征的发育障碍。已发现几种临床点突变，例如 M12K、C85R 和 Y79del，发生在 GTP 酶结构域内。然而，由于结构信息有限，Rab23 的激活机制及其临床突变体的发病机制仍不清楚。到目前为止，只有两种报道的小鼠 Rab23 与 GDP 复合的晶体结构。在这里，我们确定了人 Rab23 和人 Rab23 Y79del 临床突变体的高分辨率晶体结构，分别与 GDP 和 GMPPNP（一种不可水解的 GTP 类似物）复合。在 体外生化和功能分析的支持下，我们证明 Y79 缺失突变体相对于 WT 的区域在开关 II 区表现出结构扭曲。结构变化可能破坏了 Rab23 Y79del 与其相互作用伙伴的结合，从而导致功能丧失和 Carpenter 综合征的发展。