title: Autonomous and phosphorylation-responsive microtubule-regulating activities of the N-terminus of Op18/stathmin.
abstract: Op18 is the prototypical member of a family of phosphorylation-responsive regulators of microtubule (MT) dynamics. Previous dissection of Op18 has suggested that it has a functional dichotomy in which an intact N-terminus is required for catastrophe promotion (i.e. transition from growing to shrinking MTs), whereas an intact C-terminus is required for efficient ternary Op18-tubulin complex formation and the resultant tubulin-sequestering activity. Here we have expressed and functionally analyzed the properties of the N-terminus of Op18. The data show that the N-terminal 57 residues are sufficient for low-affinity tubulin interactions, as shown by inhibition of basal GTP hydrolysis of soluble heterodimers. In addition, high concentrations of the Op18 N-terminal portion increased the catastrophe rate during MT assembly in vitro. Overexpression of the N-terminus in a human cell line results in MT destabilization in interphase and phosphorylation-modulated accumulation of metaphase-arrested cells with dense short MTs. These results demonstrate that the N-terminus of Op18 has autonomous activity. Evidently, this activity is enhanced by the increase in tubulin affinity that is provided by the extended alpha-helical portion of native Op18.
authors.affiliation: Department of Molecular Biology, Umeå University, Sweden.
authors.forename: Bo
authors.initials: B
authors.lastname: Segerman
authors.forename: Per
authors.initials: P
authors.lastname: Holmfeldt
authors.forename: Justin
authors.initials: J
authors.lastname: Morabito
authors.forename: Lynne
authors.initials: L
authors.lastname: Cassimeris
authors.forename: Martin
authors.initials: M
authors.lastname: Gullberg
mesh_terms: D000595:Amino Acid Sequence / Q000502:physiology; D002453:Cell Cycle / Q000502:physiology; D019281:Dimerization; D005057:Eukaryotic Cells / Q000166:cytology / Q000378:metabolism*; D015870:Gene Expression / Q000502:physiology; D006160:Guanosine Triphosphate / Q000378:metabolism; D006801:Humans; D006868:Hydrolysis; D007399:Interphase / Q000502:physiology; D008677:Metaphase / Q000502:physiology; D008868:Microtubule Proteins; D008870:Microtubules / Q000378:metabolism*; D008938:Mitosis / Q000502:physiology; D010750:Phosphoproteins / Q000378:metabolism*; D010766:Phosphorylation; D017433:Protein Structure, Secondary / Q000502:physiology; D017434:Protein Structure, Tertiary / Q000502:physiology; D050777:Stathmin; D014407:Tumor Cells, Cultured
chemical_list: D008868:Microtubule Proteins; D010750:Phosphoproteins; C493995:STMN1 protein, human; D050777:Stathmin; D006160:Guanosine Triphosphate