High impact information on H-S-CoB

• All catabolic processes finally lead to the formation of a mixed disulfide from coenzyme M and coenzyme B that functions as an electron acceptor of certain anaerobic respiratory chains [1].
• Methyl-coenzyme M reductase (MCR) catalyses the reduction of methyl-coenzyme M (CH3-S-CoM) with coenzyme B (H-S-CoB) to CH4 and CoM-S-S-CoB in methanogenic archaea [2].
• The active sites of MCR from M. barkeri and M. kandleri were almost identical to that of M. thermoautotrophicum and predominantly occupied by coenzyme M and coenzyme B [3].
• Cell-free extracts of these methanogens were shown to carry out the ATP-dependent phosphorylation of N-(7-mercaptoheptanoyl)threonine to HS-HTP [4].
• 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 [5].

Biological context of H-S-CoB

• The protein product of the MJ1596 gene, designated AksF, catalyzed the NAD-dependent decarboxylation of intermediates in the biosynthesis of 7-mercaptoheptanoic acid, a moiety of methanoarchaeal coenzyme B (7-mercaptoheptanylthreonine phosphate) [6].

Associations of H-S-CoB with other chemical compounds

• Methyl-coenzyme M reductase (MCR), which catalyses the reduction of methyl-coenzyme M (CH(3)-S-CoM) with coenzyme B (H-S-CoB) to CH(4) and CoM-S-S-CoB, contains the nickel porphinoid F430 as prosthetic group [7].
• Purified methyl-CoM reductase of Methanobacterium thermoautotrophicum (strain Marburg) catalyzed the reduction of methyl-CoM to methane with reduced cobalamin, when either synthetic 7-mercaptoheptanoylthreonine phosphate (HS-HTP) or naturally occurring component B was present [8].
• Identification of enzymes homologous to isocitrate dehydrogenase that are involved in coenzyme B and leucine biosynthesis in methanoarchaea [6].
• The cofactor extracted from the protein by heat denaturation was found to comigrate with the mixed disulfide of HS-HTP and 2-mercaptoethanol by high-performance liquid chromatography, suggesting HS-HTP is not modified in the bound state [9].

Gene context of H-S-CoB

• In the presence of methyl-coenzyme M and coenzyme B the red1 signal was the same as in the presence of methyl-coenzyme M alone [10].
• Most methanogenic Archaea contain an unusual cytoplasmic fumarate reductase which catalyzes the reduction of fumarate with coenzyme M (CoM-S-H) and coenzyme B (CoB-S-H) as electron donors forming succinate and CoM-S-S-CoB as products [11].

References