2 LINES OF ALLOSTERIC COMMUNICATION IN THE OLIGOMERIC CHAPERONIN GROEL ARE REVEALED BY THE SINGLE MUTATION ARG196-]ALA

Sequence homology between GroEL and Escherichia coli DNA polymerase I, together with the fact that both proteins bind adenine nucleotides, suggested to us that they may have a similar nucleotide binding site. Arg196 in GroEL corresponds to Arg425 in DNA polymerase I, which is near its nucleotide binding site. Here, we report the striking effects of the mutation Arg196 --> Ala in GroEL on its kinetic and allosteric properties with respect to ATP. The mutation reduces positive co-operativity in ATP hydrolysis found in wild-type GroEL. It also gives rise to strong substrate (ATP) inhibition, which is not apparent in the wild-type protein. The dual effect of the mutation reflects the presence of two lines of allosteric communication between ATP binding sites in GroEL and suggests the existence of nested co-operativity.