title: GCP5 and GCP6: two new members of the human gamma-tubulin complex.
abstract: The gamma-tubulin complex is a large multiprotein complex that is required for microtubule nucleation at the centrosome. Here we report the purification and characterization of the human gamma-tubulin complex and the identification of its subunits. The human gamma-tubulin complex is a ring of ~25 nm, has a subunit structure similar to that reported for gamma-tubulin complexes from other species, and is able to nucleate microtubule polymerization in vitro. Mass spectrometry analysis of the human gamma-tubulin complex components confirmed the presence of four previously identified components (gamma-tubulin and gamma-tubulin complex proteins [GCPs] 2, 3, and 4) and led to the identification of two new components, GCP5 and GCP6. Sequence analysis revealed that the GCPs share five regions of sequence similarity and define a novel protein superfamily that is conserved in metazoans. GCP5 and GCP6, like other components of the gamma-tubulin complex, localize to the centrosome and associate with microtubules, suggesting that the entire gamma-tubulin complex takes part in both of these interactions. Stoichiometry experiments revealed that there is a single copy of GCP5 and multiple copies of gamma-tubulin, GCP2, GCP3, and GCP4 within the gamma-tubulin complex. Thus, the gamma-tubulin complex is conserved in structure and function, suggesting that the mechanism of microtubule nucleation is conserved.
authors.affiliation: Department of Biological Sciences, Stanford University, Stanford, California 94305-5020, USA.
authors.forename: S M
authors.initials: SM
authors.lastname: Murphy
authors.forename: A M
authors.initials: AM
authors.lastname: Preble
authors.forename: U K
authors.initials: UK
authors.lastname: Patel
authors.forename: K L
authors.initials: KL
authors.lastname: O'Connell
authors.forename: D P
authors.initials: DP
authors.lastname: Dias
authors.forename: M
authors.initials: M
authors.lastname: Moritz
authors.forename: D
authors.initials: D
authors.lastname: Agard
authors.forename: J T
authors.initials: JT
authors.lastname: Stults
authors.forename: T
authors.initials: T
authors.lastname: Stearns
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D002460:Cell Line; D018385:Centrosome / Q000378:metabolism; D018076:DNA, Complementary; D006801:Humans; D051379:Mice; D008807:Mice, Inbred BALB C; D008869:Microtubule-Associated Proteins / Q000145:classification / Q000235:genetics* / Q000378:metabolism*; D008969:Molecular Sequence Data; D014404:Tubulin / Q000378:metabolism*; D014407:Tumor Cells, Cultured
chemical_list: D018076:DNA, Complementary; D008869:Microtubule-Associated Proteins; C444455:TUBGCP5 protein, human; C444456:TUBGCP6 protein, human; D014404:Tubulin