Rational design of faster associating and tighter binding protein complexes

A protein design strategy was developed to specifically enhance the rate of association (k(on)) between a pair of proteins without affecting the rate of dissociation (k(off)). The method is based on increasing the electrostatic attraction between the proteins by incorporating charged residues in the vicinity of the binding interface. The contribution of mutations towards the rate of association was calculated using a newly developed computer algorithm, which predicted accurately the rate of association of mutant protein complexes relative to the wild type. Using this design strategy, the rate of association and the affinity between TEM1 beta-lactamase and its protein inhibitor BLIP was enhanced 250-fold, while the dissociation rate constant was unchanged. The results emphasize that long range electrostatic forces specifically alter k(on), but do not effect k(off). The design strategy presented here is applicable for increasing rates of association and affinities of protein complexes in general.