Cofactor A is a molecular chaperone required for beta-tubulin folding: functional and structural characterization.
Actin and tubulin polypeptide chains acquire their native conformation in the presence of the chaperonin containing TCP-1 (CCT) and, in the case of alpha- and beta-tubulin additional protein cofactors. We recently identified one of these cofactors, termed cofactor A, that is required for the proper folding of the beta-tubulin chain [Gao et al. (1994) J. Cell. Biol. 125, 989-996]. We show here that cofactor A, a monomeric protein that has no measurable affinity for nucleotides, is a highly conserved protein among vertebrates. Its NH2-terminal region is essential for the structural integrity of the protein and consequently for its activity. We demonstrate that cofactor A does not interact with CCT nor does it affect the intrinsic ATPase activity of CCT, alone or in the presence of different target proteins. Thus, unlike GroES, cofactor A does not modulate or coordinate ATP hydrolysis. It does not act as a nucleotide exchange factor or a catalyst in tubulin folding. Rather, we demonstrate that cofactor A participates in the tubulin folding process by interacting with a folding intermediate of beta-tubulin that is released from CCT. Our data imply that cofactor A is a chaperone involved in tubulin folding.
Melki
R
R
Laboratoire d'Enzymologie et Biochimie Structurales, Centre National de la Recherche Scientifique, Gif-sur-Yvette, France. melki@lebs.cnrs-gif.fr
Rommelaere
H
H
Leguy
R
R
Vandekerckhove
J
J
Ampe
C
C
D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D018833:Chaperonins; D002645:Chickens; D003001:Cloning, Molecular; D018076:DNA, Complementary; D018832:Molecular Chaperones / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D008969:Molecular Sequence Data; D011485:Protein Binding; D017510:Protein Folding; D011499:Protein Processing, Post-Translational; D011506:Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D011817:Rabbits; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D017386:Sequence Homology, Amino Acid; D012689:Sequence Homology, Nucleic Acid; D012996:Solutions; D014404:Tubulin / Q000737:chemistry* / Q000378:metabolism; D014867:Water
D018076:DNA, Complementary; D018832:Molecular Chaperones; D011506:Proteins; D011994:Recombinant Proteins; D012996:Solutions; D014404:Tubulin; C087414:chaperonin cofactor A; D014867:Water; D018833:Chaperonins