IDENTIFICATION AND FUNCTIONAL-ANALYSIS OF CHAPERONIN-10, THE GROES HOMOLOG FROM YEAST MITOCHONDRIA

Chaperonin 60 (cpn60) and chaperonin 10 (cpn10) constitute the chapero nin system in prokaryotes, mitochondria, and chloroplasts. In Escheric hia coli, these two chaperonins are also termed groEL and groES. We ha ve used a functional assay to identify the groES homolog cpn10 in yeas t mitochondria. When dimeric ribulose-1,5-bisphosphate carboxylase (Ru bisco) is denatured and allowed to bind to yeast cpn60, subsequent ref olding of Rubisco is strictly dependent upon yeast cpn10. The heterolo gous combination of cpn60 from E. coli plus yeast cpn10 is also functi onal. In contrast, yeast cpn60 plus E. coli cpn10 do not support refol ding of Rubisco. In the presence of MgATP, yeast cpn60 and yeast cpn10 form a stable complex that can be isolated by gel filtration and that facilitates refolding of denatured Rubisco. Although the potassium-de pendent ATPase activity of E. coli cpn60 can be inhibited by cpn10 fro m either E. coli or yeast, neither of these cpn10s inhibits the ATPase activity of yeast cpn60. Amino acid sequencing of yeast cpn10 reveals substantial similarity to the corresponding cpn10 proteins from rat m itochondria and prokaryotes.