All kinesins contain a motor domain or head, the position varies but it is structurally highly conserved (Kull et al. 1996, Sablin et al. 1996). The microtubule-binding site includes structural elements which interact with tubulin and undergo movement between the ADP and ATP bound states. The highly conserved switch I (SSRSH) and II (DLAGSE) motifs, which change in conformation during the ATP hydrolysis cycle, form a salt-bridge that, in myosin, closes the nucleotide-binding cleft, enabling the motor to hydrolyze ATP (Geeves & Holmes 1999). This closed conformation has now been seen in a crystal structure of the frog kinesin-5 Eg5 (Parke et al. 2010).