Evidence for rapid association-dissociation of ribonuclease T1 from a recombinant strain of Escherichia coli

On the basis of photon correlation experiments and computer simulations, we provide evidence for a rapid dimerization of the enzyme ribonuclease T1 isolated from an Escherichia coli overproducing strain. An attractive potential in addition to the usual repulsive hardcore and electrostatic potentials was found to be necessary for interpreting the concentration dependence of the diffusion coefficient of the enzyme. Computer searches of surface complementarity suggest that dimer formation of ribonuclease T1 takes place due to an extensive surface contact of approximately 700 A2. Energy minimization of the ribonuclease T1 dimer shows that large conformational changes are not induced upon self-association of the enzyme. The two molecules in the dimer are orientated back-to-back, and this is expected to lead to an active enzyme form.