Microviridins, tricyclic peptide natural products originally isolated from cyanobacteria, function as inhibitors of diverse serine-type proteases. Here we report the structure and biochemical characterization of AMdnB, a unique iterative macrocyclase involved in a microviridin biosynthetic pathway from Anabaena sp. PCC 7120. The ATPdependent cyclase, along with the homologous AMdnC, introduce up to nine macrocyclizations on three distinct core regions of a precursor peptide, AMdnA. The results presented here provide structural and mechanistic insight into the iterative chemistry of AMdnB. In vitro AMdnB-catalyzed cyclization reactions demonstrate the synthesis of the two predicted tricyclic products from a multi-core precursor peptide substrate, consistent with a distributive mode of catalysis. The X-ray structure of AMdnB shows a structural motif common to ATP-grasp cyclases involved in RiPPs biosynthesis. Additionally, comparison with the noniterative MdnB allows insight into the structural basis for the iterative chemistry. Overall, the presented results provide insight into the general mechanism of iterative enzymes in ribosomally synthesized and post-translationally modified peptide biosynthetic pathways.
Nonalcoholic fatty liver disease (NAFLD) is associated with insulin resistance and altered hepatic energy metabolism, with imbalanced glucose and lipid metabolism. Nicotinamide riboside (NR) has recently emerged as a potential therapeutic for a broad range of metabolic abnormalities. Here, we evaluate the effect of NR treatment on hepatic substrate metabolism in mice with NAFLD. NAFLD was induced by feeding the animals with a choline-deficient, amino acid-define (CDAA) diet for 4 weeks. Mice (C57BL/6) in the NR treatment group (CDAA+NR) were then put on a NR-containing CDAA diet for 10 weeks while the non-treated animals remained on CDAA. Both groups of animals had similar food consumption and weight gain rates, with comparable liver-to-body weight ratios. At the conclusion of the treatment, isolated livers were perfused via the portal vein with 13C metabolic tracers, i.e. 5.5 mM [1,6-13C]glucose + 0.4 mM [U-13C]long chain fatty acids (LCFA) suspended in bovine serum albumin. Fractional substrate oxidations and flux analyses were done using 13C nuclear magnetic resonance (NMR) spectroscopy. An increasing trend of oxygen consumption rates was observed as a result of NR treatment (1.50±0.43 µmol/min/liver) compared to the CDAA-treated group (0.68±0.15 µmol/min/liver). However, the increase is not statistically different. 13C NMR isotopomer flux analyses revealed that pyruvate dehydrogenase flux relative to citrate synthase flux are comparable across the 2 groups (CDAA: 30±4%; CDAA+NR: 33±10%). No changes in fractional oxidation of 13C-long-chain fatty acids and 13C-glucose were observed as a result of nicotinamide riboside treatment, with 44±2% and 48±3% of Ac-CoA derived from 13C-LCFA in CDAA and CDAA+NR livers, respectively. 13C-glucose contributed as a minor source of Ac-CoA (~4-5%) in both groups. These findings suggest that nicotinamide riboside treatment did not affect substrate, fats vs glucose, utilization in CDAA-induced NAFLD mouse livers. Disclosure Q. Shen: None. J.K. Pugmire: None. U. Suwannasual: None. N.R. Maptue: None. C. Khemtong: None. Funding University of Florida
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.