GCP5 and GCP6: two new members of the human gamma-tubulin complex.
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.
Murphy
S M
SM
Department of Biological Sciences, Stanford University, Stanford, California 94305-5020, USA.
Preble
A M
AM
Patel
U K
UK
O'Connell
K L
KL
Dias
D P
DP
Moritz
M
M
Agard
D
D
Stults
J T
JT
Stearns
T
T
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
D018076:DNA, Complementary; D008869:Microtubule-Associated Proteins; C444455:TUBGCP5 protein, human; C444456:TUBGCP6 protein, human; D014404:Tubulin