Natural product juglone targets three key enzymes from Helicobacter pylori: inhibition assay with crystal structure characterization

AIM: To investigate the inhibition features of the natural product juglone (5-hydroxy-1,4-naphthoquinone) against the three key enzymes from Helicobacter pylori (cystathionine γ-synthase [HpCGS], malonyl-CoA:acyl carrier protein transacylase [HpFabD], and β-hydroxyacyl-ACP dehydratase [HpFabZ]). METHODS: An enzyme inhibition assay against HpCGS was carried out by using a continuous coupled spectrophotometric assay approach. The inhibition assay of HpFabD was performed based on the α-ketoglutarate dehydrogenase-coupled system, while the inhibition assay for HpFabZ was monitored by detecting the decrease in absorbance at 260 nm with crotonoyl-CoA conversion to β-hydroxybutyryl-CoA. The juglone/FabZ complex crystal was obtained by soaking juglone into the HpFabZ crystal, and the X-ray crystal structure of the complex was analyzed by molecular replacement approach. RESULTS: Juglone was shown to potently inhibit HpCGS, HpFabD, and HpFabZ with the half maximal inhibitory concentration IC(50) values of 7.0±0.7, 20±1, and 30±4 μmol/L, respectively. An inhibition-type study indicated that juglone was a non-competitive inhibitor of HpCGS against O-succinyl-L-homoserine (K(i)=αK(i)=24 μmol/L), an uncompetitive inhibitor of HpFabD against malonyl-CoA (αK(i)=7.4 μmol/L), and a competitive inhibitor of HpFabZ against crotonoyl-CoA (K(i)=6.8 μmol/L). Moreover, the crystal structure of the HpFabZ/juglone complex further revealed the essential binding pattern of juglone against HpFabZ at the atomic level. CONCLUSION: HpCGS, HpFabD, and HpFabZ are potential targets of juglone.