Figure 6. Conserved motifs in kinesin-binding protein (KBP)-binding kinesin MDs.

(a) Sequence alignment of the tubulin-binding subdomain from kinesin motor domains, made using Clustal Omega multiple sequence alignment (Sievers et al., 2011). Residues are coloured according to standard Clustal X colouring (dependent on residue type and conservation, see http://bioinfolab.unl.edu/emlab/documents/clustalx_doc/clustalx.html#C). Kinesin MD constructs experimentally assessed for KBP interactivity are taken from Kevenaar et al., 2016; strongest interactors are in rows highlighted in darker shades of green, weaker interactors in lighter shades of green, and non-interactors in red. Secondary structure element, conservation and charge variation columns, as well as a ‘binding consensus’ column indicating residues/loop length conserved at the interface (according to the KBP–KIF15_MD6S complex) in KBP-binding but not non-binding kinesins are shown above the alignment. Non-conservation relative to this consensus is shown in boxed sequence; red boxes, non-conservative substitutions, orange boxes, conservative substitutions (general charge/polarity/hydrophobicity retention), cyan boxes, extended loop region, dark blue boxes, truncated loop region. (b) Top panel; view of the Kβ4–KL8 region of the tubulin-binding subdomain in the KBP–KIF15_MD6S model, coloured as in Figure 4. Bottom panel; as in upper panel, but with the KIF11_MD cryo-electron microscopy model (PDB: 6TA4 [Peña et al., 2020]) superimposed onto the now hidden KBP–KIF15_MD6S. Note steric clash introduced by KIF11_MD’s extended KL8. (c) Schematic model of KBP’s hypothesised selective kinesin inhibition mechanism. KBP (olive) binds the compatible TBsd of recognised kinesins (magenta) but is incompatible with the TBsd of non-binding kinesins (salmon). For its target kinesins, KBP therefore sterically blocks the TBsd interaction with MTs (grey), preventing activation of kinesin ATPase and motility.