ABSTRACT
The sugar-facilitated structure and enzymatic activity change of engineered myoglobins bearing a phenylboronic acid moiety, which were semisynthesized by a cofactor reconstitution method, were studied by the denaturation experiment, spectrophotometric titration of the pKa shift of the axial H2O, circular dichloism (CD), and the kinetics of the myoglobin-catalyzed-aniline hydroxylation reaction. Both boronophenylalanine-appended myoglobin [Mb(m-Bphe)2] and phenylboronic acid-appended myoglobin [Mb(PhBOH)2] were stabilized by approximately 2 kcal/mol upon complexation with D-fructose. CD spectral changes and the sugar-induced pKa shift suggested that the microenvironment of the active site of these myoglobins was re-formed from a partially disturbed state to that comparable to the native state upon D-fructose binding. The correlation of pKa with kcat (for the aniline hydroxylase activity) and the delta GDH2O-kcat profile showed that these structural changes of Mb-(m-Bphe)2 and Mb(PhBOH)2 were closely related to their sugar-enhanced aniline hydroxylase activity. Thus, the results established that an incorporation of the artificial receptor molecule can be a valid methodology for the design of stimuli-responsive semiartificial enzymes.
