Coenzyme B Explained

Coenzyme B is a coenzyme required for redox reactions in methanogens. The full chemical name of coenzyme B is 7-mercaptoheptanoylthreoninephosphate.^[1] The molecule contains a thiol, which is its principal site of reaction.

Coenzyme B reacts with 2-methylthioethanesulfonate (methyl-Coenzyme M, abbreviated), to release methane in methanogenesis:^[2]

+ HS–CoB → + CoB–S–S–CoMThis conversion is catalyzed by the enzyme methyl coenzyme M reductase, which contains cofactor F430 as the prosthetic group.

A related conversion that utilizes both HS-CoB and HS-CoM is the reduction of fumarate to succinate, catalyzed by fumarate reductase:^[3]

HS–CoM + HS–CoB + ⁻ → ⁻ + CoB–S–S–CoM

Importance of Coenzyme B in Methanogenesis

Coenzyme B is an important component in the terminal step of methane biogenesis.^[4] It acts as a two electron-donor to reduce coenzyme M (methyl-coenzyme) into two molecules a methane and a heterodisulfide.^[5] Two separate experiment that were performed, one with coenzyme B and other without coenzyme B, indicated that using coenzyme B before the formation of the methane molecule, results in a more efficient and consistent bond cleavage.^[6]

Notes and References

1. Noll KM, Rinehart KL, Tanner RS, Wolfe RS . Structure of component B (7-mercaptoheptanoylthreonine phosphate) of the methylcoenzyme M methylreductase system of Methanobacterium thermoautotrophicum . Proceedings of the National Academy of Sciences. 83 . 12 . 4238–42 . 1986 . 3086878 . 10.1073/pnas.83.12.4238 . 323707. 1986PNAS...83.4238N . free .
2. Thauer RK . Biochemistry of methanogenesis: a tribute to Marjory Stephenson. 1998 Marjory Stephenson Prize Lecture . Microbiology . 144 . Pt 9 . 2377–406 . September 1998 . 9782487 . 10.1099/00221287-144-9-2377 . free .
3. Heim S, Künkel A, Thauer RK, Hedderich R . Thiol:fumarate reductase (Tfr) from Methanobacterium thermoautotrophicum—identification of the catalytic sites for fumarate reduction and thiol oxidation . European Journal of Biochemistry. 253 . 1 . 292–9 . April 1998 . 9578488 . 10.1046/j.1432-1327.1998.2530292.x. free .
4. Dey. Mishtu. Li. Xianghui. Kunz. Ryan C. Ragsdale. Stephen W. 2010-12-22. Detection of Organometallic and Radical Intermediates in the Catalytic Mechanism of Methyl-Coenzyme M Reductase Using the Natural Substrate Methyl-Coenzyme M and a Coenzyme B Substrate Analogue. Biochemistry. 49. 51. 10902–10911. 10.1021/bi101562m. 21090696.
5. Cedervall. Peder E. Dey. Mishtu. Pearson. Arwen R. Ragsdale. Stephen W. Wilmot. Carrie M. 2010-07-22. Structural Insight into Methyl-Coenzyme M Reductase Chemistry Using Coenzyme B Analogues. Biochemistry. 49. 35. 7683–7693. 10.1021/bi100458d. 20707311. 3098740.
6. Horng. Yih-Chern. Becker. Donald F. Ragsdale. Stephen W. 2001-10-30. Mechanistic Studies of Methane Biogenesis by Methyl-Coenzyme M Reductase: Evidence that Coenzyme B Participates in Cleaving the C−S Bond of Methyl-Coenzyme M. Biochemistry. 40. 43. 12875–12885. 10.1021/bi011196y. 11669624.