Bryan J. Johnson, Jordi Cohen, Richard W. Welford, Arwen R. Pearson, Klaus Schulten, Judith P. Klinman, and Carrie M. Wilmot. Exploring molecular oxygen pathways in Hanseluna Polymorpha copper-containing amine oxidase. Journal of Biological Chemistry, 282:17767-17776, 2007. (PMC: 3081669)

JOHN2007 The accessibility of large substrates to buried enzymatic active sites is dependent upon the utilization of proteinaceous channels. The necessity of these channels in the case of small substrates is questionable as diffusion through the protein matrix is often assumed. Copper amine oxidases (CAOs) contain a buried protein-derived quinone cofactor and a mononuclear copper center that catalyze the conversion of two substrates, primary amines and molecular oxygen, to aldehydes and hydrogen peroxide respectively. The nature of molecular oxygen migration to the active site in the enzyme from Hansenula polymorpha (HPAO) is explored using a combination of kinetic, X-ray crystallographic and computational approaches. A crystal structure of HPAO in complex with xenon gas, which serves as an experimental probe for molecular oxygen binding sites, reveals buried regions of the enzyme suitable for transient molecular oxygen occupation. The calculation of O$_2$ free energy maps corresponds well with the xenon binding sites, and helps connect individual sites into routes with differing probabilities. Site-directed mutagenesis designed to block individual routes has little effect on overall $k_{cat}$/$K_m$[O$_2$], supporting multiple dynamic pathways for molecular oxygen to reach the active site.


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