Gradient bundle analysis of ketosteroid isomerase

Bond bundle analysis is used to investigate enzymatic catalysis in the KSI active site. We identify the unique bonding regions in each system and calculate the precise redistribution of electron density that accompanies either enhancement or inhibition of KSI catalytic activity. In two examples—using direct inspection of bond bundle regional properties, and using correlations between those properties and reaction barrier height—we arrive at similar conclusions, that cat- alytic enhancement results from promoting electron density redistribution between bonds within the KSI-docked substrate molecule in a way that closely resembles our mechanistic understanding of the forward catalyzed reaction. This catalyzing charge redistribution is prevalent in KSI systems catalyzed via electric fields or via amino acid mutation, and are thus suggestive of a significant catalytic role. Bond bundle analysis also generates a wealth of statistically useful bond properties, making it a strong candidate for machine learning approaches to computer- aided artificial enzyme design, and a promising tool for the discovery of relationships between the structure of the electron charge density and enzymatic catalytic activity.