title: The unique hetero-oligomeric nature of the subunits in the catalytic cooperativity of the yeast Cct chaperonin complex.
abstract: The structural and functional organization of the Cct complex was addressed by genetic analyses of subunit interactions and catalytic cooperativity among five of the eight different essential subunits, Cct1p-Cct8p, in the yeast Saccharomyces cerevisiae. The cct1-1, cct2-3, and cct3-1 alleles, containing mutations at the conserved putative ATP-binding motif, GDGTT, are cold-sensitive, whereas single and multiple replacements of the corresponding motif in Cct6p are well tolerated by the cell. We demonstrated herein that cct6-3 (L19S), but not the parolog cct1-5 (R26I), specifically suppresses the cct1-1, cct2-3, and cct3-1 alleles, and that this suppression can be modulated by mutations in a putative phosphorylation motif, RXS, and the putative ATP-binding pocket of Cct6p. Our results suggest that the Cct ring is comprised of a single hetero-oligomer containing eight subunits of differential functional hierarchy, in which catalytic cooperativity of ATP-binding/hydrolysis takes place in a sequential manner different from the concerted cooperativity proposed for GroEL.
authors.affiliation: Department of Biochemistry and Biophysics, University of Rochester Medical School, Rochester, NY 14642, USA.
authors.forename: P
authors.initials: P
authors.lastname: Lin
authors.forename: F
authors.initials: F
authors.lastname: Sherman
mesh_terms: D000595:Amino Acid Sequence; D001704:Biopolymers; D002384:Catalysis; D018834:Chaperonin 60 / Q000737:chemistry / Q000378:metabolism; D018833:Chaperonins / Q000737:chemistry / Q000378:metabolism*; D005816:Genetic Complementation Test; D008969:Molecular Sequence Data; D010766:Phosphorylation; D012441:Saccharomyces cerevisiae / Q000235:genetics / Q000378:metabolism*; D013329:Structure-Activity Relationship
chemical_list: D001704:Biopolymers; D018834:Chaperonin 60; D018833:Chaperonins