Phosphate ester hydrolysis is catalyzed by a bacterial transferrin: potential implications for in vivo iron transport mechanisms

Abstract Two synergistic anions, p -nitrophenyl phosphate ester ( NPP ) and SO 4 2 - , were found to form new stable assemblies with Fe 3+ and a bacterial transferrin, FbpA (FbpA = ferric binding protein). Fe 3+ FbpA–SO 4 undergoes rapid anion exchange in the presence of NPP to form Fe 3+ FbpA–NPP. Formation of Fe 3+ FbpA–NPP was found to accelerate the rate of hydrolysis of the bound phosphate ester ( k hyd  = 1.6 × 10 −6 s −1 at 25 °C and pH 6.5) by >10 3 fold over the uncatalyzed reaction. These findings suggest a dual function for FbpA in vivo: transport of Fe 3+ across the periplasmic space to the inner membrane in certain gram-negative bacteria and hydrolysis of periplasmic polyphosphates.