title: Chaperonin-mediated folding of vertebrate actin-related protein and gamma-tubulin.
abstract: The folding of actin and tubulin is mediated via interaction with a heteromeric toroidal complex (cytoplasmic chaperonin) that hydrolyzes ATP as part of the reaction whereby native proteins are ultimately released. Vertebrate actin-related protein (actin-RPV) (also termed centractin) and gamma-tubulin are two proteins that are distantly related to actin and tubulin, respectively: gamma-tubulin is exclusively located at the centrosome, while actin-RPV is conspicuously abundant at the same site. Here we show that actin-RPV and gamma-tubulin are both folded via interaction with the same chaperonin that mediates the folding of beta-actin and alpha- and beta-tubulin. In each case, the unfolded polypeptide forms a binary complex with cytoplasmic chaperonin and is released as a soluble, monomeric protein in the presence of Mg-ATP and the presence or absence of Mg-GTP. In contrast to alpha- and beta-tubulin, the folding of gamma-tubulin does not require the presence of cofactors in addition to chaperonin itself. Monomeric actin-RPV produced in in vitro folding reactions cocycles efficiently with native brain actin, while in vitro folded gamma-tubulin binds to polymerized microtubules in a manner consistent with interaction with microtubule ends. Both monomeric actin-RPV and gamma-tubulin bind to columns of immobilized nucleotide: monomeric actin-RPV has no marked preference for ATP or GTP, while gamma-tubulin shows some preference for GTP binding. We show that actin-RPV and gamma-tubulin compete with one another, and with beta-actin or alpha-tubulin, for binary complex formation with cytoplasmic chaperonin.
authors.affiliation: Department of Biochemistry, New York University Medical Center, New York 10016.
authors.forename: R
authors.initials: R
authors.lastname: Melki
authors.forename: I E
authors.initials: IE
authors.lastname: Vainberg
authors.forename: R L
authors.initials: RL
authors.lastname: Chow
authors.forename: N J
authors.initials: NJ
authors.lastname: Cowan
mesh_terms: D000199:Actins / Q000737:chemistry* / Q000378:metabolism; D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D001483:Base Sequence; D001667:Binding, Competitive; D002417:Cattle; D018833:Chaperonins; D006160:Guanosine Triphosphate / Q000378:metabolism; D008297:Male; D051379:Mice; D008969:Molecular Sequence Data; D010452:Peptide Biosynthesis; D011485:Protein Binding; D011487:Protein Conformation; D011506:Proteins / Q000378:metabolism / Q000502:physiology*; D011817:Rabbits; D012156:Reticulocytes / Q000737:chemistry / Q000378:metabolism; D014404:Tubulin / Q000737:chemistry* / Q000378:metabolism
chemical_list: D000199:Actins; D011506:Proteins; D014404:Tubulin; C076834:centractin; D006160:Guanosine Triphosphate; D000255:Adenosine Triphosphate; D018833:Chaperonins