Rational enzyme design presents a major challenge that has not been overcome by computational approaches. One of the key challenges is the difficulty in assessing the magnitude of the maximum possible catalytic activity. In an attempt to overcome this challenge, we introduce a strategy that takes an active enzyme (assuming that its activity is close to the maximum possible activity), design mutations that reduce the catalytic activity, and then try to restore that catalysis by mutating other residues. Here we take as a test case the enzyme haloalkane dehalogenase (DhlA), with a 1,2-dichloroethane substrate. We start by demonstrating our ability to reproduce the results of single mutations. Next, we design mutations that reduce the enzyme activity and finally design double mutations that are aimed at restoring the activity. Using the computational predictions as a guide, we conduct an experimental study that confirms our prediction in one case and leads to inconclusive results in another case with 1,2-dichloroethane as substrate. Interestingly, one of our predicted double mutants catalyzes dehalogenation of 1,2-dibromoethane more efficiently than the wild-type enzyme.

Department of Chemistry University of Southern California Los Angeles CA 90089

Loschmidt Laboratories Department of Experimental Biology Masaryk University 625 00 Brno Czech Republic

Loschmidt Laboratories Department of Experimental Biology Masaryk University 625 00 Brno Czech Republic Research Centre for Toxic Compounds in the Environment Masaryk University 625 00 Brno Czech Republic International Clinical Research Center St Anne's University Hospital 656 91 Brno Czech Republic

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