Crystal structure of a dynamin GTPase domain in both nucleotide-free and GDP-bound forms

Dynamins form a family of multidomain GTPases involved in endocytosis, vesicle trafficking and maintenance of mitochondrial morphology. In contrast to the classical switch GTPases, a force-generating function has been suggested for dynamins. Here we report the 2.3 Å crystal structure of the nucleotide-free and GDP-bound GTPase domain of Dictyostelium discoideum dynamin A. The GTPase domain is the most highly conserved region among dynamins. The globular structure contains the G-protein core fold, which is extended from a six-stranded β-sheet to an eight-stranded one by a 55 amino acid insertion. This topologically unique insertion distinguishes dynamins from other subfamilies of GTP-binding proteins. An additional N-terminal helix interacts with the C-terminal helix of the GTPase domain, forming a hydrophobic groove, which could be occupied by C-terminal parts of dynamin not present in our construct. The lack of major conformational changes between the nucleotide-free and the GDP-bound state suggests that mechanochemical rearrangements in dynamin occur during GTP binding, GTP hydrolysis or phosphate release and are not linked to loss of GDP.

动力蛋白（dynamin）是一类多结构域GTP酶（GTPase）家族，参与胞吞作用、囊泡运输以及线粒体形态维持。与经典开关型GTP酶不同，已有研究提示动力蛋白具备产力功能。本文报道了盘基网柄菌（Dictyostelium discoideum）动力蛋白A的无核苷酸态与GDP结合态GTP酶结构域（GTPase domain）的2.3埃晶体结构。GTP酶结构域是动力蛋白家族中保守性最高的区域。该球状结构包含G蛋白核心折叠，其由六链β折叠片通过一段55个氨基酸的插入序列延伸为八链β折叠片。这一拓扑学上独特的插入序列，是动力蛋白区别于GTP结合蛋白其他亚家族的标志性特征。一段额外的N端螺旋与GTP酶结构域的C端螺旋相互作用，形成一个疏水凹槽，该凹槽可被本研究构建体未包含的动力蛋白C端区域所占据。无核苷酸态与GDP结合态之间未出现显著构象变化，这提示动力蛋白的机械化学重排发生于GTP结合、GTP水解或磷酸释放阶段，而非与GDP解离相关。