Exploring the Origin of Amidase Substrate Promiscuity in CALB by a Computational Approach

Enzyme promiscuity attracts the interest of the industrial and academic sectors because of its application in the design of biocatalysts. The amidase activity of Candida antarctica lipase B (CALB) on two different substrates has been studied by theoretical quantum mechanics/molecular mechanics methods, supported by experimental kinetic measurements. The aim of the study is to understand the substrate promiscuity of CALB in this secondary reaction and the origin of its promiscuous catalytic activity. The computational results predict activation free energies in very good agreement with the kinetic data and confirm that the activity of CALB as an amidase, despite depending on the features of the amide substrate, is dictated by the electrostatic effects of the protein. The protein polarizes and activates the substrate as well as stabilizes the transition state, thus enhancing the rate constant. Our results can provide guides for future designs of biocatalysts based on electrostatic arguments