Structure determination of the UDP-disaccharide fragment of cytoplasmic cofactor isolated from Methanobacterium thermoautotrophicum

Inhibition of methylcoenzyme M methylreductase by a uridine 5'-diphospho-N-acetylglucosamine derivative

Uridine-5'-diphospho-N-acetylglucosamine, when oxidized with periodate to the corresponding aldehyde (o-UDP-GlcNAc), was a potent inhibitor of the methylcoenzyme M methylreductase reaction which catalyzes the reductive demethylation of methylcoenzyme M to methane. The oxidation product, o-UDP-GlcNAc, appears to bind to the UDP-GlcNAc site of the enzyme and inhibits the reduction of methylcoenzyme M both by MRF or its active hydrolytic fragment HS-HTP. The kinetic patterns indicate that o-UDP-GlcNAc inhibition is noncompetitive with HS-HTP or MRF, and the Hill coefficient indicated that there was cooperativity between the UDP and HS-HTP binding sites. The methylreductase enzyme was protected from o-UDP-GlcNAc inhibition by prior exposure to low concentrations of MRF. HS-HTP, at the same concentration as MRF, was not effective in protecting the enzyme from inhibition by o-UDP-GlcNAc.

Comparison of the biosynthesis of the methanobacterial pseudomurein and the eubacterial murein

From cell extracts of the archaebacterium Methanobacterium thermoautotrophicum 11 putative precursors of the pseudomurein were isolated and characterized. On the basis of the isolated intermediates, a biosynthetic pathway of the pseudomurein is proposed. Compared to the eubacterial murein the biosynthetic stages follow different pathways as indicated by the occurrence of a nucleotide-activated disaccharide and nucleotide-activated peptides.

Structure of a novel cofactor containing N-(7-mercaptoheptanoyl)-O-3-phosphothreonine

The cofactor required in the methylcoenzyme M methylreductase reaction was shown to be a large molecule with an Mr of 1149.21 in the free acid form. The cofactor, named MRF for methyl reducing factor, was identified from analyses by fast atom bombardment mass spectrometry and 1H, 13C, and 31P NMR spectroscopy as uridine 5'-[N-(7-mercaptoheptanoyl)-O-3-phosphothreonine-P-yl(2-acetamido- 2-deoxy- beta-mannopyranuronosyl)(acid anhydride)]-(1----4)-O-2-acetamido-2-deoxy- alpha-glucopyranosyl diphosphate. MRF contains N-(7-mercaptoheptanoyl)threonine O-3-phosphate (HS-HTP) [No11, K. M., Rinehart, K. L., Tanner, R. S., & Wolfe, R. S. (1986) Proc. Natl. Acad. Sci. U.S.A. 83, 4238-4242] and is linked to C-6 of 2-acetamido-2-deoxymannopyranuronic acid of the UDP-disaccharide through a carboxylic-phosphoric anhydride linkage. It is postulated that this bond is responsible for the instability of the molecule and its hydrolysis during isolation. Analyses of Eadie and Hofstee plots of the methylcoenzyme M methylreductase reaction indicate that MRF has a 6-fold lower Km(app) than HS-HTP and a 50% greater Vmax. This suggests that the UDP-disaccharide moiety may be of importance in the binding of MRF to the enzyme active site.

Stimulation of the methylcoenzyme M reduction by uridine-5'-diphospho-sugars in cell-free extracts of Methanobacterium thermoautotrophicum (strain delta H)

The hydrogen-dependent reduction of methylcoenzyme M catalyzed by coenzyme-depleted cell-free extracts of Methanobacterium thermoautotrophicum was stimulated by micromolar concentrations of a UDP-disaccharide present in the organism. The compound was isolated and identified as UDP-1-O-alpha-D-2-acetamido-2-deoxyglucopyranose (UDPGlcpNAc) glycosidically linked to 2-acetamido-2-deoxymannopyranosyluronic acid. Maximal stimulation was observed when both the UDP-disaccharide and mercaptoheptanoylthreonine phosphate were present in the reaction mixtures. The UDP derivative isolated was not specific in its action: other UDP-sugars tested in micromolar concentrations stimulated the methylcoenzyme M reduction to the same extent. The activated sugars presumably substitute for ATP, which is usually required in much higher concentrations to activate the methylcoenzyme M reductase system.