Escherichia coli GroEL and GroES are the prototypical chaperonin and co-chaperonin. Chaperonins are ring-shaped molecular chaperone proteins that are found in all organisms and are essential for protein folding and protection from stress. Both the chaperonin and co-chaperonin are 7-fold symmetric oligomers. GroEL is composed of fourteen identical 60 kDa subunits arranged in two stacked rings, and GroES is composed of a seven identical 10 kDa subunits.