title: Origin and evolution of eukaryotic chaperonins: phylogenetic evidence for ancient duplications in CCT genes.
abstract: Chaperonins are oligomeric protein-folding complexes which are divided into two distantly related structural classes. Group I chaperonins (called GroEL/cpn60/hsp60) are found in bacteria and eukaryotic organelles, while group II chaperonins are present in archaea and the cytoplasm of eukaryotes (called CCT/TriC). While archaea possess one to three chaperonin subunit-encoding genes, eight distinct CCT gene families (paralogs) have been characterized in eukaryotes. We are interested in determining when during eukaryotic evolution the multiple gene duplications producing the CCT subunits occurred. We describe the sequence and phylogenetic analysis of five CCT genes from TRICHOMONAS: vaginalis and seven from GIARDIA: lamblia, representatives of amitochondriate protist lineages thought to have diverged early from other eukaryotes. Our data show that the gene duplications producing the eight CCT paralogs took place prior to the organismal divergence of TRICHOMONAS: and GIARDIA: from other eukaryotes. Thus, these divergent protists likely possess completely hetero-oligomeric CCT complexes like those in yeast and mammalian cells. No close phylogenetic relationship between the archaeal chaperonins and specific CCT subunits was observed, suggesting that none of the CCT gene duplications predate the divergence of archaea and eukaryotes. The duplications producing the CCTdelta and CCTepsilon subunits, as well as CCTalpha, CCTbeta, and CCTeta, are the most recent in the CCT gene family. Our analyses show significant differences in the rates of evolution of archaeal chaperonins compared with the eukaryotic CCTs, as well as among the different CCT subunits themselves. We discuss these results in light of current views on the origin, evolution, and function of CCT complexes.
authors.affiliation: Department of Biochemistry and Molecular Biology, Dalhousie University, Halifax, Nova Scotia, Canada. jmarchib@is2.dal.ca
authors.forename: J M
authors.initials: JM
authors.lastname: Archibald
authors.forename: J M
authors.initials: JM
authors.lastname: Logsdon
authors.forename: W F
authors.initials: WF
authors.lastname: Doolittle
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001105:Archaea / Q000235:genetics; D018833:Chaperonins / Q000235:genetics*; D056890:Eukaryota / Q000235:genetics*; D005057:Eukaryotic Cells; D019143:Evolution, Molecular; D020440:Gene Duplication; D017125:Genes, Protozoan; D016829:Giardia lamblia / Q000235:genetics; D047908:Intracellular Signaling Peptides and Proteins; D016013:Likelihood Functions; D008869:Microtubule-Associated Proteins; D008969:Molecular Sequence Data; D009687:Nuclear Proteins / Q000235:genetics*; D010802:Phylogeny; D017386:Sequence Homology, Amino Acid; D014246:Trichomonas vaginalis / Q000235:genetics; D044767:Ubiquitin-Protein Ligases; D056427:t-Complex Genome Region
chemical_list: D047908:Intracellular Signaling Peptides and Proteins; D008869:Microtubule-Associated Proteins; D009687:Nuclear Proteins; C116196:PPP1R11 protein, human; D044767:Ubiquitin-Protein Ligases; D018833:Chaperonins