PhLP3 modulates CCT-mediated actin and tubulin folding via ternary complexes with substrates.
Many ATP-dependent molecular chaperones, including Hsp70, Hsp90, and the chaperonins GroEL/Hsp60, require cofactor proteins to regulate their ATPase activities and thus folding functions in vivo. One conspicuous exception has been the eukaryotic chaperonin CCT, for which no regulator of its ATPase activity, other than non-native substrate proteins, is known. We identify the evolutionarily conserved PhLP3 (phosducin-like protein 3) as a modulator of CCT function in vitro and in vivo. PhLP3 binds CCT, spanning the cylindrical chaperonin cavity and contacting at least two subunits. When present in a ternary complex with CCT and an actin or tubulin substrate, PhLP3 significantly diminishes the chaperonin ATPase activity, and accordingly, excess PhLP3 perturbs actin or tubulin folding in vitro. Most interestingly, however, the Saccharomyces cerevisiae PhLP3 homologue is required for proper actin and tubulin function. This cellular role of PhLP3 is most apparent in a strain that also lacks prefoldin, a chaperone that facilitates CCT-mediated actin and tubulin folding. We propose that the antagonistic actions of PhLP3 and prefoldin serve to modulate CCT activity and play a key role in establishing a functional cytoskeleton in vivo.
Stirling
Peter C
PC
Department of Molecular Biology and Biochemistry, Simon Fraser University, Burnaby, British Columbia V5A 1S6, Canada.
Cuéllar
Jorge
J
Alfaro
Gabriel A
GA
El Khadali
Fatima
F
Beh
Christopher T
CT
Valpuesta
José M
JM
Melki
Ronald
R
Leroux
Michel R
MR
D000199:Actins / Q000737:chemistry; D000255:Adenosine Triphosphate / Q000737:chemistry; D000818:Animals; D002352:Carrier Proteins / Q000737:chemistry / Q000502:physiology*; D002417:Cattle; D002460:Cell Line; D056404:Chaperonin Containing TCP-1; D018833:Chaperonins / Q000737:chemistry; D003599:Cytoskeleton / Q000378:metabolism; D017353:Gene Deletion; D005982:Glutathione Transferase / Q000378:metabolism; D006801:Humans; D007091:Image Processing, Computer-Assisted; D008297:Male; D008854:Microscopy, Electron; D008870:Microtubules / Q000378:metabolism; D009419:Nerve Tissue Proteins / Q000737:chemistry / Q000502:physiology*; D010641:Phenotype; D011485:Protein Binding; D014176:Protein Biosynthesis; D017510:Protein Folding; D017434:Protein Structure, Tertiary; D034622:RNA Interference; D011994:Recombinant Proteins / Q000737:chemistry; D012441:Saccharomyces cerevisiae / Q000378:metabolism; D013379:Substrate Specificity; D013696:Temperature; D013737:Testis / Q000378:metabolism; D013997:Time Factors; D014404:Tubulin / Q000737:chemistry
D000199:Actins; D002352:Carrier Proteins; D009419:Nerve Tissue Proteins; C498322:PDCL3 protein, human; D011994:Recombinant Proteins; D014404:Tubulin; D000255:Adenosine Triphosphate; D005982:Glutathione Transferase; D056404:Chaperonin Containing TCP-1; D018833:Chaperonins