Example 2
Expressed and purified dihydropteroate synthase (DHPS) from S. aureus (saDHPS) was cloned. DHPS is the enzyme that installs PABA (p-aminobenzoic acid) in the folate biosynthesis pathway (Scheme 2). It has been demonstrated that the PABA analog PAS (2-aminosalicylate) is incorporated into folic acid in M. tuberculosis (Chakraborty, S. et al. 2013), suggesting that PAS is a substrate for DHPS. Using a coupled assay, it was determined that the kinetic parameters for saDHPS with PABA, PAS and F-PABA. Importantly, all three compounds have similar kcat and Km values indicating that F-PABA is an alternative substrate for saDHPS. Since PAS is an antibacterial compound whose mechanism of action may be related for the ability of this compound to compete with PABA for DHPS, we determined the antibacterial activity and cytotoxicity of F-PABA for several bacterial species as well as Vero cells. In each case no growth inhibition was observed up to 200 μg/ml. Unlike PAA, 2-F-PABA has no antibacterial activity (Table 1).
