Centrioles are microtubule-based cylindrical ultrastructures characterized by their definite size and robustness. The molecular capping protein, CPAP (also known as CENPJ) engages its N-terminal region with the centriole microtubules to regulate their length. Nevertheless, the conserved C-terminal glycine-rich G-box of CPAP, which interacts with the centriole inner cartwheel protein STIL, is frequently mutated in primary microcephaly (MCPH) patients. Here, we show that two different MCPH-associated variants, E1235V and D1196N in the CPAP G-box, affect distinct functions at centrioles. The E1235V mutation reduces CPAP centriole recruitment and causes overly long centrioles. The D1196N mutation increases centriole numbers without affecting centriole localization. Both mutations prevent binding to STIL, which controls centriole duplication. Our work highlights the involvement of an alternative CEP152-dependent route for CPAP centriole localization. Molecular dynamics simulations suggest that E1235V leads to an increase in G-box flexibility, which could have implications on its molecular interactions. Collectively, we demonstrate that a CPAP region outside the microtubule-interacting domains influences centriole number and length, which translates to spindle defects and reduced cell viability. Our work provides new insights into the molecular causes of primary microcephaly.

中文翻译：

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CPAP 功能分离 MCPH 相关突变影响中心粒数量和长度。

中心粒是基于微管的圆柱形超微结构，其特征在于其确定的尺寸和坚固性。分子加帽蛋白 CPAP（也称为 CENPJ）将其 N 末端区域与中心粒微管接合以调节其长度。然而，CPAP 保守的 C 端富含甘氨酸的 G 盒与中心粒内车轮蛋白 STIL 相互作用，在原发性小头畸形 (MCPH) 患者中经常发生突变。在这里，我们展示了 CPAP G 盒中的两种不同的 MCPH 相关变体，E1235V 和 D1196N，影响中心粒的不同功能。E1235V 突变减少了 CPAP 中心粒的募集并导致中心粒过长。D1196N 突变增加了中心粒数量，但不影响中心粒定位。这两种突变都阻止与控制中心粒复制的 STIL 结合。我们的工作强调了 CPAP 中心粒定位的替代 CEP152 依赖途径的参与。分子动力学模拟表明，E1235V 导致 G-box 灵活性增加，这可能对其分子相互作用产生影响。总的来说，我们证明微管相互作用域之外的 CPAP 区域会影响中心粒的数量和长度，这会导致纺锤体缺陷和细胞活力降低。我们的工作为原发性小头畸形的分子原因提供了新的见解。