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

ABSTRACT

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 gamma-synthase [HpCGS], malonyl-CoAacyl carrier protein transacylase [HpFabD], and beta-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 alpha-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 beta -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 IC50 values of 7.0 +/-0.7, 20 +/-1, and 30 +/-4 micromol/L, respectively. An inhibition-type study indicated that juglone was a non-competitive inhibitor of HpCGS against O-succinyl- L-homoserine (Ki=alphaKi=24 micromol/L), an uncompetitive inhibitor of HpFabD against malonyl-CoA (alphaKi=7.4 micromol/L), and a competitive inhibitor of HpFabZ against crotonoyl-CoA (Ki=6.8 micromol/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.