AbstractWe employed a minimalist approach for design of an allosterically controlled retroaldolase. Introduction of a single lysine residue into the nonenzymatic protein calmodulin led to a 15,000‐fold increase in the second order rate constant for retroaldol reaction with methodol as a substrate. The resulting catalyst AlleyCatR is active enough for subsequent directed evolution in crude cell bacterial lysates. AlleyCatR's activity is allosterically regulated by Ca2+ ions. No catalysis is observed in the absence of the metal ion. The increase in catalytic activity originates from the hydrophobic interaction of the substrate (∼2000‐fold) and the change in the apparent pKa of the active lysine residue.