title: Microtubule-driven multimerization recruits ase1p onto overlapping microtubules.
abstract: Microtubule (MT) crosslinking proteins of the ase1p/PRC1/Map65 family play a major role in the construction of MT networks such as the mitotic spindle. Most homologs in this family have been shown to localize with a remarkable specificity to sets of MTs that overlap with an antiparallel relative orientation [1-4]. Regulatory proteins bind to ase1p/PRC1/Map65 and appear to use the localization to set up precise spatial signals [5-10]. Here, we present evidence for a mechanism of localized protein multimerization underlying the specific targeting of ase1p, the fision yeast homolog. In controlled in vitro experiments, dimers of ase1-GFP diffused along the surface of single MTs and, at concentrations above a certain threshold, assembled into static multimeric structures. We observed that this threshold was significantly lower on overlapping MTs. We also observed diffusion and multimerization of ase1-GFP on MTs inside living cells, suggesting that a multimerization-driven localization mechanism is relevant in vivo. The domains responsible for MT binding and multimerization were identified via a series of ase1p truncations. Our findings show that cells use a finely tuned cooperative localization mechanism that exploits differences in the geometry and concentration of ase1p binding sites along single and overlapping MTs.
authors.affiliation: Department of Physics and Astronomy, VU University Amsterdam, De Boelelaan 1081, 1081 HV Amsterdam, The Netherlands.
authors.forename: Lukas C
authors.initials: LC
authors.lastname: Kapitein
authors.forename: Marcel E
authors.initials: ME
authors.lastname: Janson
authors.forename: Siet M J L
authors.initials: SM
authors.lastname: van den Wildenberg
authors.forename: Casper C
authors.initials: CC
authors.lastname: Hoogenraad
authors.forename: Christoph F
authors.initials: CF
authors.lastname: Schmidt
authors.forename: Erwin J G
authors.initials: EJ
authors.lastname: Peterman
mesh_terms: D000818:Animals; D019556:COS Cells; D002522:Chlorocebus aethiops; D008869:Microtubule-Associated Proteins / Q000378:metabolism*; D008870:Microtubules / Q000378:metabolism*; D011485:Protein Binding; D054730:Protein Interaction Domains and Motifs; D055503:Protein Multimerization; D012568:Schizosaccharomyces / Q000378:metabolism / Q000648:ultrastructure*; D029702:Schizosaccharomyces pombe Proteins / Q000378:metabolism*
chemical_list: C502827:Ase1 protein, S pombe; D008869:Microtubule-Associated Proteins; D029702:Schizosaccharomyces pombe Proteins