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| Title | Conformational switching and flexibility in cobalamin-dependent methionine synthase studied by small-angle X-ray scattering and cryoelectron microscopy. |
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| Journal, issue, pages | Proc Natl Acad Sci U S A, Vol. 120, Issue 26, Page e2302531120, Year 2023 |
| Publish date | Jun 27, 2023 |
 Authors | Maxwell B Watkins / Haoyue Wang / Audrey Burnim / Nozomi Ando /  |
| PubMed Abstract | Cobalamin-dependent methionine synthase (MetH) catalyzes the synthesis of methionine from homocysteine and 5-methyltetrahydrofolate (CH-Hfolate) using the unique chemistry of its cofactor. In doing ...Cobalamin-dependent methionine synthase (MetH) catalyzes the synthesis of methionine from homocysteine and 5-methyltetrahydrofolate (CH-Hfolate) using the unique chemistry of its cofactor. In doing so, MetH links the cycling of -adenosylmethionine with the folate cycle in one-carbon metabolism. Extensive biochemical and structural studies on MetH have shown that this flexible, multidomain enzyme adopts two major conformations to prevent a futile cycle of methionine production and consumption. However, as MetH is highly dynamic as well as both a photosensitive and oxygen-sensitive metalloenzyme, it poses special challenges for structural studies, and existing structures have necessarily come from a "divide and conquer" approach. In this study, we investigate MetH and a thermophilic homolog from using small-angle X-ray scattering (SAXS), single-particle cryoelectron microscopy (cryo-EM), and extensive analysis of the AlphaFold2 database to present a structural description of the full-length MetH in its entirety. Using SAXS, we describe a common resting-state conformation shared by both active and inactive oxidation states of MetH and the roles of CH-Hfolate and flavodoxin in initiating turnover and reactivation. By combining SAXS with a 3.6-Å cryo-EM structure of the MetH, we show that the resting-state conformation consists of a stable arrangement of the catalytic domains that is linked to a highly mobile reactivation domain. Finally, by combining AlphaFold2-guided sequence analysis and our experimental findings, we propose a general model for functional switching in MetH. |
 External links | Proc Natl Acad Sci U S A / PubMed:37339208 / PubMed Central |
| Methods | EM (single particle) |
| Resolution | 3.6 Å |
| Structure data | EMDB-29699, PDB-8g3h: |
| Chemicals |  ChemComp-ZN:  ChemComp-B12: |
| Source |
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 Keywords | TRANSFERASE / Methyltransferase / Amino-acid biosynthesis / Methionine biosynthesis |
thermus filiformis (bacteria)