Functional role of residues involved in substrate binding of human 4-hydroxyphenylpyruvate dioxygenase.

4-Hydroxylphenylpyruvate dioxygenase (HPPD) catalyzes the conversion of 4-hydroxylphenylpyruvate (HPP) to homogentisate, the important step for tyrosine catabolism. Comparison of the structure of human HPPD with the substrate-bound structure of A. thaliana HPPD revealed notably different orientations of the C-terminal helix. This helix performed as a closed conformation in human enzyme. Simulation revealed a different substrate-binding mode in which the carboxyl group of HPP interacted by a H-bond network formed by Gln334, Glu349 (the metal-binding ligand), and Asn363 (in the C-terminal helix). The 4-hydroxyl group of HPP interacted with Gln251 and Gln265. The relative activity and substrate-binding affinity were preserved for the Q334A mutant, implying the alternative role of Asn363 for HPP binding and catalysis. The reduction in kcat/Km of the Asn363 mutants confirmed the critical role in catalysis. Compared to the N363A mutant, the dramatic reduction in the Kd and thermal stability of the N363D mutant implies the side-chain effect in the hinge region rotation of the C-terminal helix. The activity and binding affinity were not recovered by double mutation; however, the 4-hydroxyphenylacetate intermediate formation by the uncoupled reaction of Q334N/N363Q and Q334A/N363D mutants indicated the importance of the H-bond network in the electrophilic reaction. These results highlight the functional role of the H-bond network in a closed conformation of the C-terminal helix to stabilize the bound substrate. The extremely low activity and reduction in Q251E's Kd suggest that interaction coupled with the H-bond network is crucial to locate the substrate for nucleophilic reaction.

Anti-inflammatory effect of water extracts of Graptopetalum paraguayense supplementation in subjects with metabolic syndrome: a preliminary study.

BACKGROUND: Many studies have demonstrated that Graptopetalum paraguayense has good antioxidant ability; however, few studies have examined its anti-inflammatory effect. The study aimed to investigate the anti-inflammatory effects of water extracts of G. paraguayense (WGP, 4 g day(-1)) in subjects with metabolic syndrome (MS). Intervention was administered for 12 weeks. Levels of inflammatory markers [high sensitivity C-reactive protein (CRP), tumour necrosis factor-α (TNF-α), and interleukin-6 (IL-6)] and antioxidant enzymes activities were measured. RESULTS: Forty-two subjects completed the 12 week intervention study (placebo, n = 19; WGP, n = 23). After 12 weeks supplementation, subjects in WGP group had significantly lower levels of inflammatory markers than the baseline (P < 0.05) and the placebo group (CRP, P = 0.07; TNF-α, P = 0.04; IL-6, P = 0.03). The changes in levels of the inflammatory markers were significantly decreased in WGP group (CRP, P = 0.04; TNF-α, P = 0.06; IL-6, P = 0.01) compared to the placebo group. Levels of inflammatory markers were significantly negatively correlated with the antioxidant enzymes activities after supplementation. CONCLUSION: This study demonstrated a significant reduction in inflammatory status in MS after WGP supplementation. WGP may exert an anti-inflammatory effect on MS in addition to its antioxidant ability.

Effects of water extracts of Graptopetalum paraguayense on blood pressure, fasting glucose, and lipid profiles of subjects with metabolic syndrome.

This study was aimed to investigate the effects of water extracts of Graptopetalum paraguayense (WGP, 4 g/d) on blood pressure, blood glucose level, and lipid profiles in subjects with metabolic syndrome (MS). Participants with MS (n = 54) were randomly assigned to the placebo (n = 28) and WGP groups (n = 26), and the intervention was administered for 12 weeks. Systolic blood pressure (SBP), diastolic blood pressure (DBP), fasting glucose (FG), lipid profiles (total cholesterol (TC), triglyceride (TG), low density lipoprotein cholesterol (LDL-C), and high density lipoprotein (HDL-C)), and antioxidant enzymes activities (catalase (CAT), superoxide dismutase (SOD), and glutathione peroxidase (GPx)) were measured. Forty-two subjects completed the study (placebo, n = 19; WGP, n = 23). FG, SBP, and LDL-C levels were significantly lower and HDL-C level and antioxidant enzymes activities (CAT and SOD) were significantly higher after WGP supplementation. Blood pressure, FG, and lipid profiles were significantly correlated with antioxidant enzymes activities after supplementation (P < 0.05). The present study demonstrated a significant reduction in blood pressure, blood glucose, and lipid profiles and an increase in antioxidant enzymes activities in subjects with MS after WGP supplementation. Taken together, the antioxidative capacity of WGP might exert a beneficial effect on MS. This trial is registered with ClinicalTrials.gov NCT01463748.