The C-terminal α-helix of SPAS-1, a Caenorhabditis elegans spastin homologue, is crucial for microtubule severing.

Spastin belongs to the meiotic subfamily, together with Vps4/SKD1, fidgetin and katanin, of AAA (ATPases associated with diverse cellular activities) proteins, and functions in microtubule severing. Interestingly, all members of this subgroup specifically contain an additional α-helix at the very C-terminal end. To understand the function of the C-terminal α-helix, we characterised its deletion mutants of SPAS-1, a Caenorhabditis elegans spastin homologue, in vitro and in vivo. We found that the C-terminal α-helix plays essential roles in ATP binding, ATP hydrolysing and microtubule severing activities. It is likely that the C-terminal α-helix is required for cellular functions of members of meiotic subgroup of AAA proteins, since the C-terminal α-helix of Vps4 is also important for assembly, ATPase activity and in vivo function mediated by ESCRT-III complexes.