title: Phosphorylation by Cdk1 increases the binding of Eg5 to microtubules in vitro and in Xenopus egg extract spindles.
abstract: BACKGROUND
  Motor proteins from the kinesin-5 subfamily play an essential role in spindle assembly during cell division of most organisms. These motors crosslink and slide microtubules in the spindle. Kinesin-5 motors are phosphorylated at a conserved site by Cyclin-dependent kinase 1 (Cdk1) during mitosis. Xenopus laevis kinesin-5 has also been reported to be phosphorylated by Aurora A in vitro.
  
  
  RESULTS
  We investigate here the effect of these phosphorylations on kinesin-5 from Xenopus laevis, called Eg5. We find that phosphorylation at threonine 937 in the C-terminal tail of Eg5 by Cdk1 does not affect the velocity of Eg5, but strongly increases its binding to microtubules assembled in buffer. Likewise, this phosphorylation promotes binding of Eg5 to microtubules in Xenopus egg extract spindles. This enhancement of binding elevates the amount of Eg5 in spindles above a critical level required for bipolar spindle formation. We find furthermore that phosphorylation of Xenopus laevis Eg5 by Aurora A at serine 543 in the stalk is not required for spindle formation.
  
  
  CONCLUSIONS
  These results show that phosphorylation of Eg5 by Cdk1 has a direct effect on the interaction of this motor with microtubules. In egg extract, phosphorylation of Eg5 by Cdk1 ensures that the amount of Eg5 in the spindle is above a level that is required for spindle formation. This enhanced targeting to the spindle appears therefore to be, at least in part, a direct consequence of the enhanced binding of Eg5 to microtubules upon phosphorylation by Cdk1. These findings advance our understanding of the regulation of this essential mitotic motor protein.
authors.affiliation: European Molecular Biology Laboratory, Cell Biology and Biophysics Unit, Heidelberg, Germany.
authors.forename: Julie
authors.initials: J
authors.lastname: Cahu
authors.forename: Aurelien
authors.initials: A
authors.lastname: Olichon
authors.forename: Christian
authors.initials: C
authors.lastname: Hentrich
authors.forename: Henry
authors.initials: H
authors.lastname: Schek
authors.forename: Jovana
authors.initials: J
authors.lastname: Drinjakovic
authors.forename: Cunjie
authors.initials: C
authors.lastname: Zhang
authors.forename: Amanda
authors.initials: A
authors.lastname: Doherty-Kirby
authors.forename: Gilles
authors.initials: G
authors.lastname: Lajoie
authors.forename: Thomas
authors.initials: T
authors.lastname: Surrey
mesh_terms: D000818:Animals; D002021:Buffers; D016203:CDC2 Protein Kinase / Q000378:metabolism*; D002457:Cell Extracts; D019926:Cyclin B / Q000378:metabolism; D016547:Kinesins / Q000172:deficiency / Q000378:metabolism*; D008870:Microtubules / Q000201:enzymology*; D010063:Ovum / Q000201:enzymology*; D010766:Phosphorylation; D011485:Protein Binding; D008941:Spindle Apparatus / Q000201:enzymology*; D014981:Xenopus / Q000378:metabolism*; D029867:Xenopus Proteins / Q000172:deficiency / Q000378:metabolism*
chemical_list: D002021:Buffers; D002457:Cell Extracts; D019926:Cyclin B; C088335:KIF11 protein, Xenopus; D029867:Xenopus Proteins; D016203:CDC2 Protein Kinase; D016547:Kinesins