Inhibition of the Bacterial Surface Protein Anchoring Transpeptidase Sortase by Medicinal Plants

Inhibition by medicinal plant extracts of a recombinant sortase was evaluated for antibacterial drug discovery. The coding region of sortase, a transpeptidase that cleaves surface proteins of Gram-positive bacteria, was amplified by PCR from the chromosome of Staphylococcus aureus ATCC 6538p with the exception of an N-terminal membrane anchor sequence, expressed in Escherichia coli, and purified by metal chelate affinity chromatography. The purified sortase had maximum activity at pH 7.5 and was stable at 20-45°C for the cleavage of a synthetic fluorophore substrate. The enzyme inhibitory activity in medicinal plants was also evaluated for antibacterial drug discovery. Among 80 medicinal plants tested, Cocculus trilobus, Fritillaria verticillata, Liriope platyphylla, and Rhus verniciflua had strong inhibitory activity. The extract with the greatest activity was the ethyl acetate fraction derived from the rhizome of Cocculus trilobus (IC₅₀=1.52 μg/ml).