The Role of Allosteric Networks in Facilitating Enzymatic Catalysis of the Homodimer, Fluoroacetate Dehalogenase

Many oligomeric enzymes act through half-of-the-sites reactivity, in which the substrate engages with only one protomer at a time. In the case of the homodimeric enzyme, fluoroacetate dehalogenase, vacancy of one protomer is required for catalytic function. Substrate binding to one protomer induces disorder in the empty protomer, entropically driving the reaction forward. The enzyme utilizes a regulatory cap domain above the substrate access channel which prohibits substrate access to the empty protomer. At high substrate concentrations, a second substrate binds to a site along the binding channel of the occupied protomer, inhibiting catalysis. A key mutation of this site, K152I, effectively halts second site binding, resulting in abrogation of substrate inhibition and an order of magnitude drop in catalytic rate. At low substrate concentrations, the allosteric pocket acts as a conduit to desolvate the substrate. These results illustrate the role of dynamics along allosteric networks in facilitating chemical function.