Inhibition of the dapE-Encoded N‑Succinyl‑l,l‑diaminopimelic Acid Desuccinylase from Neisseria meningitidis by l‑Captopril

Binding of the competitive inhibitor l-captopril to the dapE-encoded N-succinyl-l,l-diaminopimelic acid desuccinylase from Neisseria meningitidis (NmDapE) was examined by kinetic, spectroscopic, and crystallographic methods. l-Captopril, an angiotensin-converting enzyme (ACE) inhibitor, was previously shown to be a potent inhibitor of the DapE from Haemophilus influenzae (HiDapE) with an IC₅₀ of 3.3 μM and a measured K_i of 1.8 μM and displayed a dose-responsive antibiotic activity toward Escherichia coli. l-Captopril is also a competitive inhibitor of NmDapE with a K_i of 2.8 μM. To examine the nature of the interaction of l-captopril with the dinuclear active site of DapE, we have obtained electron paramagnetic resonance (EPR) and magnetic circular dichroism (MCD) data for the enzymatically hyperactive Co­(II)-substituted forms of both HiDapE and NmDapE. EPR and MCD data indicate that the two Co­(II) ions in DapE are antiferromagnetically coupled, yielding an S = 0 ground state, and suggest a thiolate bridge between the two metal ions. Verification of a thiolate-bridged dinuclear complex was obtained by determining the three-dimensional X-ray crystal structure of NmDapE in complex with l-captopril at 1.8 Å resolution. Combination of these data provides new insights into binding of l-captopril to the active site of DapE enzymes as well as important inhibitor–active site residue interaction’s. Such information is critical for the design of new, potent inhibitors of DapE enzymes.