Insight into molecular mechanism underlying the transesterification catalysed by penicillin G amidase (PGA) using a combination protocol of experimental assay and theoretical analysis

Penicillin G amidase (PGA) is one of the most recognised biocatalysts because of its critical application in the antibiotic industry. Herein, the additive effects involved in transesterification catalysed by PGA are explored in detail using a combination of experimental analysis and theoretical modelling. The transesterification ability of PGA is experimentally determined with 17 N-containing compounds as additives, and, on this basis, a series of quantitative structure–activity relationship (QSAR) models are developed from various physicochemical parameters characterising structural variation over the additives. The resulting models exhibit both good stability and predictive power, from which five most important properties that highlight structural basis and reaction mechanism underlying the transesterification are extracted, revealing that the topological property and electrostatic profile of additives exert a significant effect on reaction yield; the charge distribution around additive molecules is the most significant factor controlling reaction yield, and then the topological structure. Furthermore, it is inferred that the additive imidazole might constitute the catalytic triad of Ser, Glu or Asp involved in PGA active site, which appears similar to lipase, rendering PGA with the catalytic ability of transesterfication. The study highlights the potential application of QSAR methodology in the field of enzymatic regulator design.