Rate Enhancement of an Interfacial Biochemical Reaction through Localization of Substrate and Enzyme by an Adaptor Domain

This paper describes a model system to characterize the rate enhancement that stems from localization of an enzyme with its substrate. The approach is based on a self-assembled monolayer that presents a substrate for the serine esterase cutinase along with a peptide ligand for an SH2 adaptor domain. The monolayer is treated with a fusion protein of cutinase and the SH2 domain, and the rate for the interfacial reaction is monitored using cyclic voltammetry. The rate is approximately 30-fold greater for monolayers that present the ligand for the SH2 domain than for those that omit the ligand. The rate enhancement is due to the interaction of the adaptor domain with the immobilized ligand. Further, the rate enhancement increases with the densities of both the ligand and the substrate. This example provides a well-defined model system for quantitatively assessing the magnitude of rate enhancement that is possible with colocalization of an enzyme with its substrate and may be particularly significant for understanding the signaling events that rely on enzyme localization at the cell membrane.