InterPro domain: IPR002423

The assembly of proteins has been thought to be the sole result of properties inherent in the primary sequence of polypeptides themselves. In some cases, however, structural information from other protein molecules is required for correct folding and subsequent assembly into oligomers [ 1 ]. These 'helper' molecules are referred to as molecular chaperones, a subfamily of which are the chaperonins [ 2 ], which include 10kDa and 60kDa proteins. These are found in abundance in prokaryotes, chloroplasts and mitochondria. They are required for normal cell growth (as demonstrated by the fact that no temperature sensitive mutants for the chaperonin genes can be found in the temperature range 20 to 43 degrees centigrade [ 3 ]), and are stress-induced, acting to stabilise or protect disassembled polypeptides under heat-shock conditions [ 3 ].

The 10kDa chaperonin (cpn10 - or groES in bacteria) exists as a ring-shaped oligomer of between 6 to 8 identical subunits, whereas the 60kDa chaperonin (cpn60 - or groEL in bacteria) forms a structure comprising 2 stacked rings, each ring containing 7 identical subunits [ 3 ]. These ring structures assemble by self-stimulation in the presence of Mg2+-ATP. The cpn10 and cpn60 oligomers also require Mg2+-ATP in order to interact to form a functional complex, although the mechanism of this interaction is as yet unknown [ 3 ]. This chaperonin complex is essential for the correct folding and assembly of polypeptides into oligomeric structures, of which the chaperonins themselves are not a part [ 4 ]. The binding of cpn10 to cpn60 inhibits the weak ATPase activity of cpn60.

TCP-1 (t-complex polypeptide 1) is a subunit of the hetero-oligomeric complex CCT (chaperonin containing TCP- 1) present in the eukaryotic cytosol. It is a member of the chaperonin family which includes GroEL, 60kDa heat shock protein (Hsp60), Rubisco subunit binding protein (RBP) and thermophilic factor 55 (TF55) [ 4 ].

1. Homologous plant and bacterial proteins chaperone oligomeric protein assembly. Nature 333, 330-4
2. cDNA clones encoding Arabidopsis thaliana and Zea mays mitochondrial chaperonin HSP60 and gene expression during seed germination and heat shock. Plant Mol. Biol. 18, 873-85
3. Cloning, sequencing, mapping, and transcriptional analysis of the groESL operon from Bacillus subtilis. J. Bacteriol. 174, 3993-9
4. The chaperonin containing t-complex polypeptide 1 (TCP-1). Multisubunit machinery assisting in protein folding and assembly in the eukaryotic cytosol. Eur. J. Biochem. 230, 3-16