A NOVEL AMINOPEPTIDASE ASSOCIATED WITH THE 60 KDA CHAPERONIN IN THE THERMOPHILIC ARCHAEON SULFOLOBUS-SOLFATARICUS

The chaperonins are high-molecular-weight protein complexes having a c haracteristic double-ring toroidal shape; they are thought to aid the folding of denatured or newly synthesized polypeptides. These proteins exist as two functionally similar but distantly related families, one including the bacterial and organellar chaperonins and the other (ter med the CCT-TRiC family) including the chaperonins of the Archaea and the eukaryotes. The CCT-TRiC chaperonins, particularly their archeal m embers, are less well known than their bacterial counterparts, and the ir main cellular function is still doubtful. In this work, we report t hat the chaperonin of the thermophilic archaeon Sulfolobus solfataricu s interacts with several polypeptides other than the two subunits that constitute the 18-mer double-ring structure. We have cloned and seque nced the gene encoding one 90 kDa chaperonin-associated protein and ha ve shown, using biochemical assays, that the product is an enzyme belo nging to the family of zinc-dependent aminopeptidases, The Sulfolobus protein shows maximal homology to eukaryotic (yeast and mouse) aminope ptidases. It contains a leucine zipper motif and can be phosphorylated by an unidentified kinase present in the cell extracts. The possible significance of an association between an aminopeptidase and a chapero nin is discussed.