Section of Structural Biology, Institute of Cancer Research, Chester Beatty Laboratories, 237 Fulham Road, London SW3 6JB, UK.
J Mol Biol. 2010 Feb 5;395(5):908-15. doi: 10.1016/j.jmb.2009.11.029. Epub 2009 Nov 17.
Mcph1 is mutated in autosomal recessive primary microcephaly and premature chromosome condensation (PCC) syndrome. Increased chromosome condensation is a common feature of cells isolated from patients afflicted with either disease. Normal cells depleted of Mcph1 also exhibit PCC phenotype. Human Mcph1 contains three BRCA1-carboxyl terminal (BRCT) domains, the first of which (Mcph1N) is necessary for the prevention of PCC. The only known disease-associated missense mutation in Mcph1 resides in this domain (T27R). We have determined the X-ray crystal structure of human Mcph1N to 1.6 A resolution. Compared with other BRCT domain structures, the most striking differences are an elongated, ordered beta1-alpha1 loop and an adjacent hydrophobic pocket. This pocket is in the equivalent structural position to the phosphate binding site of BRCT domains that recognize phospho-proteins, although the phosphate-binding residues are absent in Mcph1N. Mutations in the pocket abrogate the ability of full-length Mcph1 to rescue the PCC phenotype of Mcph1(-/-) mouse embryonic fibroblast cells, suggesting that it forms an essential part of a protein-protein interaction site necessary to prevent PCC.
Mcph1 突变可导致常染色体隐性原发性小头畸形和过早染色体凝聚（PCC）综合征。从患有这两种疾病的患者分离出的细胞中，染色体凝聚增加是一个常见特征。耗尽 Mcph1 的正常细胞也表现出 PCC 表型。人 Mcph1 含有三个 BRCA1-羧基末端（BRCT）结构域，其中第一个（Mcph1N）对于预防 PCC 是必需的。唯一已知的 Mcph1 疾病相关错义突变位于该结构域（T27R）。我们已经确定了人 Mcph1N 的 X 射线晶体结构，分辨率为 1.6A。与其他 BRCT 结构域结构相比，最显著的差异是一个拉长的、有序的β1-α1 环和一个相邻的疏水性口袋。该口袋位于 BRCT 结构域识别磷酸化蛋白的磷酸结合位点的等效结构位置，尽管 Mcph1N 中不存在磷酸结合残基。该口袋中的突变会使全长 Mcph1 丧失挽救 Mcph1（-/-）小鼠胚胎成纤维细胞 PCC 表型的能力，表明它形成了一个必需的蛋白-蛋白相互作用位点的重要部分，对于预防 PCC 是必需的。
