title: On the oligomeric state of chloroplast chaperonin 10 and chaperonin 20.
abstract: Type I chaperonins are fundamental protein folding machineries that function in eubacteria, mitochondria and chloroplasts. Eubacteria and mitochondria contain chaperonin systems comprised of homo-oligomeric chaperonin 60 tetradecamers and co-chaperonin 10 heptamers. In contrast, the chloroplast chaperonins are heterooligomeric tetradecamers that are composed of two subunit types, alpha and beta. Additionally, chloroplasts contain two structurally distinct co-chaperonins. One, ch-cpn10, is probably similar to the mitochondrial and bacterial co-chaperonins, and is composed of 10 kDa subunits. The other, termed ch-cpn20 is composed of two cpn10-like domains that are held together by a short linker. While the oligomeric structure of ch-cpn10 remains to be elucidated, it was previously suggested that ch-cpn20 forms tetramers in solution, and that this is the functional oligomer. In the present study, we investigated the properties of purified ch-cpn10 and ch-cpn20. Using bifunctional cross-linking reagents, gel filtration chromatography and analytical ultracentrifugation, we show that ch-cpn10 is a heptamer in solution. In contrast, ch-cpn20 forms multiple oligomers that are in dynamic equilibrium with each other and cover a broad spectrum of molecular weights in a concentration-dependent manner. However, upon association with GroEL, only one type of co-chaperonin-GroEL complex is formed.
mesh_terms: D000818:Animals; D017360:Arabidopsis / Q000235:genetics / Q000378:metabolism; D029681:Arabidopsis Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D018835:Chaperonin 10 / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D018834:Chaperonin 60 / Q000737:chemistry / Q000378:metabolism; D018833:Chaperonins / Q000235:genetics / Q000378:metabolism*; D002736:Chloroplasts / Q000737:chemistry / Q000378:metabolism*; D003432:Cross-Linking Reagents / Q000737:chemistry; D056384:Group I Chaperonins; D046911:Macromolecular Substances; D008291:Malate Dehydrogenase / Q000737:chemistry / Q000378:metabolism; D011108:Polymers / Q000737:chemistry / Q000378:metabolism; D017510:Protein Folding; D021122:Protein Subunits / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D013552:Swine
chemical_list: D029681:Arabidopsis Proteins; D018835:Chaperonin 10; D018834:Chaperonin 60; C478767:Cpn20 protein, Arabidopsis; D003432:Cross-Linking Reagents; D046911:Macromolecular Substances; D011108:Polymers; D021122:Protein Subunits; D008291:Malate Dehydrogenase; D018833:Chaperonins; D056384:Group I Chaperonins