Structures in Tetrahydrofolate Methylation in Desulfitobacterial Glycine Betaine Metabolism at Atomic Resolution

Chembiochem. 2020 Mar 16;21(6):776-779. doi: 10.1002/cbic.201900515. Epub 2019 Nov 18.


Enzymes orchestrating methylation between tetrahydrofolate (THF) and cobalamin (Cbl) are abundant among all domains of life. During energy production in Desulfitobacterium hafniense, MtgA catalyzes the methyl transfer from methylcobalamin (Cbl-CH3 ) to THF in the catabolism of glycine betaine (GB). Despite its lack of sequence identity with known structures, we could show that MtgA forms a homodimeric complex of two TIM barrels. Atomic crystallographic insights into the interplay of MtgA with THF as well as analysis of a trapped reaction intermediate (THF-CH3 )+ reveal conformational rearrangements during the transfer reaction. Whereas residues for THF methylation are conserved, the binding mode for the THF glutamyl-p-aminobenzoate moiety (THF tail) is unique. Apart from snapshots of individual reaction steps of MtgA, structure-based mutagenesis combined with enzymatic activity assays allowed a mechanistic description of the methyl transfer between Cbl-CH3 and THF. Altogether, the THF-tail-binding motion observed in MtgA is unique compared to other THF methyltransferases and therefore contributes to the general understanding of THF-mediated methyl transfer.

Keywords: anaerobic bacteria; cobalamin; glycine betaine metabolism; methyl transfer; tetrahydrofolate.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Bacterial Proteins / chemistry
  • Bacterial Proteins / metabolism
  • Betaine / chemistry
  • Betaine / metabolism*
  • Biocatalysis
  • Crystallography, X-Ray
  • Desulfitobacterium / chemistry*
  • Desulfitobacterium / metabolism
  • Methylation
  • Models, Molecular
  • Molecular Structure
  • Tetrahydrofolates / chemistry
  • Tetrahydrofolates / metabolism*


  • Bacterial Proteins
  • Tetrahydrofolates
  • Betaine
  • 5,6,7,8-tetrahydrofolic acid

Supplementary concepts

  • Desulfitobacterium hafniense