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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.