The katanin p80 α1 N-terminal region is distinct from SPR2 α1, and plays a role in binding factors that localize to microtubule minus ends.

(A) Sequence alignment of the N-terminal region, including α1, from the A.t. SPR2 C-terminal domain and the A.t. and Mus musculus (M.m.) p80 katanin C-terminal domain. Conservation across SPR2 homologs from Fig 1B is indicated on the SPR2 sequence. M.m. p80 residues involved in contacts with p60 are highlighted in light blue. Residues conserved between M.m. p80 and A.t. p80 over the region modeled in the 5NBT [52] structure are highlighted dark cyan (100% identity) and light orange (100% similarity) on the A.t. p80 sequence. Residue numbers are for A.t. SPR2 (above the alignment) and M.m. p80 (below the alignment). Secondary structure is indicated above for SPR2 based on the crystal structure (residues 717–736), and predicted using Jpred4 (for residues 649–716, which were either not present (degraded) or ordered in the construct crystallized), while the secondary structure for M.m. p80 is shown below based on the 5NBT structure [52]. Proline residues in the SPR2 sequence that are N-terminal to α1 and within the equivalent span that constitutes α1 in the M.m. p80 structure are colored red. (B) Structural alignment of the SPR2 C-terminal domain and the katanin p60:p80 heterodimer from 5NBT [52], oriented as in Fig 6D, with SPR2 shown in surface representation with conservation mapped as in Fig 4A. (C) Electrostatic surface potential mapped on the katanin p60:p80 heterodimer structure [52] (left image oriented as in B, right image after a 180° rotation about the y-axis). (D) Structural alignment of the mouse katanin p60:p80 heterodimerization module in complex with the microtubule minus end-binding proteins: Abnormal spindle-like microcephaly-associated protein homolog (ASPM, PDB accession code 5LB7 [51], shown in stick format, colored orange) and CAMSAP3 (PDB accession code 5OW5 [53], shown in stick format, colored chartreuse). The p60 and p80 chains are only shown from the 5LB7 structure for simplicity. Image at upper left depicts p60 and p80 chains in cartoon format with the region boxed in black shown in zoom view (lower right) with p60 and p80 depicted in surface format.