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The Bambusa oldhamii phenylalanine ammonia-lyase (PAL) proteins, BoPAL1 and BoPAL2, exhibited different substrate specificities toward phenylalanine (Phe) and tyrosine (Tyr). Mutational analysis was conducted to study their substrate selectivity. All expressed wild -type and mutant BoPAL proteins manifested PAL activity; however, K-m and k(cat) values were varied. BoPAL1 F133H and BoPAL2 F134H showed decreased k(cat)/K-m values toward phenylalanine and significantly increased tyrosine ammonia-lyase (TAL) activities. BoPAL1 V197I and BoPAL2 I198 V showed opposite results regarding TAL activity, indicating that the Val or Ile residue prior to the active site, Ala-Ser-Gly, is essential for modulating Phe/Tyr substrate selectivity.

Staphylocoagulase (Coa) is a virulence factor of Staphylococcus aureus (S. aureus) that promotes blood coagulation by activating prothrombin to convert fibrinogen to fibrin. Coa plays a crucial role in disease pathogenesis and is a promising target for the treatment of S. aureus infections. Here, we identified that isoquercitrin, a natural flavonol compound, can markedly reduce the activity of Coa at concentrations that have no effect on bacterial growth. Mechanistic studies employing molecular dynamics simulation revealed that isoquercitrin binds to Coa by interacting with Asp-181 and Tyr-188, thereby affecting the binding of Coa to prothrombin. Importantly, in vivo studies showed that isoquercitrin treatment significantly reduced the bacterial burden, pathological damage, and inflammation of lung tissue and improved the percentage of survival of mice infected with S. aureus Newman strain. These data suggest that isoquercitrin is a promising inhibitor of Coa that can be used for the development of therapeutic drugs to combat S. aureus infections.