The leucine aminopeptidase of Staphylococcus aureus is secreted and contributes to biofilm formation

Background: Staphylococcus aureus has emerged as a major drug-resistant pathogen in hospital- and community-acquired infections. Leucine aminopeptidase (LAP) is known to be essential for survival of the bacteria; however the LAP of S. aureus has not been extensively characterized. In this study, we report a detailed characterization of the S. aureus LAP. Methods: LAP from S. aureus was cloned, purified, and further biochemically characterized. The expression of LAP was analyzed by Western blotting. Growth and biofilm formation were analyzed spectrophotometrically. Results: LAP was cloned from S. aureus and expressed as a 55 kDa protein, whereas the molecular weight of the native protein is approximately 600 kDa. LAP showed amidolytic activity against l-leucine p-nitroanilide. Optimal activity was observed at pH 8.5 and 37°C with a V_max of 2500μmol/min/mg protein. LAP enzymatic activity was inhibited by ion chelators and enhanced by divalent metal ions, specifically Ni. LAP is secreted by laboratory as well as clinical strains. Bestatin, an inhibitor of LAP, inhibits S. aureus growth and biofilm formation. Conclusions: To our knowledge, this is the first detailed characterization of LAP from S. aureus and suggests its importance in survival and pathogenesis.