title: A 5-formyltetrahydrofolate cycloligase paralog from all domains of life: comparative genomic and experimental evidence for a cryptic role in thiamin metabolism.
abstract: A paralog (here termed COG0212) of the ATP-dependent folate salvage enzyme 5-formyltetrahydrofolate cycloligase (5-FCL) occurs in all domains of life and, although typically annotated as 5-FCL in pro- and eukaryotic genomes, is of unknown function. COG0212 is similar in overall structure to 5-FCL, particularly in the substrate binding region, and has distant similarity to other kinases. The Arabidopsis thaliana COG0212 protein was shown to be targeted to chloroplasts and to be required for embryo viability. Comparative genomic analysis revealed that a high proportion (19%) of archaeal and bacterial COG0212 genes are clustered on the chromosome with various genes implicated in thiamin metabolism or transport but showed no such association between COG0212 and folate metabolism. Consistent with the bioinformatic evidence for a role in thiamin metabolism, ablating COG0212 in the archaeon Haloferax volcanii caused accumulation of thiamin monophosphate. Biochemical and functional complementation tests of several known and hypothetical thiamin-related activities (involving thiamin, its breakdown products, and their phosphates) were, however, negative. Also consistent with the bioinformatic evidence, the COG0212 proteins from A. thaliana and prokaryote sources lacked 5-FCL activity in vitro and did not complement the growth defect or the characteristic 5-formyltetrahydrofolate accumulation of a 5-FCL-deficient (ΔygfA) Escherichia coli strain. We therefore propose (a) that COG0212 has an unrecognized yet sometimes crucial role in thiamin metabolism, most probably in salvage or detoxification, and (b) that is not a 5-FCL and should no longer be so annotated.
authors.affiliation: Horticultural Sciences Department, University of Florida, Gainesville, 32611, USA.
authors.forename: Anne
authors.initials: A
authors.lastname: Pribat
authors.forename: Ian K
authors.initials: IK
authors.lastname: Blaby
authors.forename: Aurora
authors.initials: A
authors.lastname: Lara-Núñez
authors.forename: Linda
authors.initials: L
authors.lastname: Jeanguenin
authors.forename: Romain
authors.initials: R
authors.lastname: Fouquet
authors.forename: Océane
authors.initials: O
authors.lastname: Frelin
authors.forename: Jesse F
authors.initials: JF
authors.lastname: Gregory
authors.forename: Benjamin
authors.initials: B
authors.lastname: Philmus
authors.forename: Tadhg P
authors.initials: TP
authors.lastname: Begley
authors.forename: Valérie
authors.initials: V
authors.lastname: de Crécy-Lagard
authors.forename: Andrew D
authors.initials: AD
authors.lastname: Hanson
mesh_terms: D000595:Amino Acid Sequence; D017360:Arabidopsis / Q000201:enzymology / Q000235:genetics*; D029681:Arabidopsis Proteins / Q000737:chemistry / Q000145:classification / Q000235:genetics* / Q000378:metabolism; D001426:Bacterial Proteins / Q000737:chemistry / Q000145:classification / Q000235:genetics* / Q000378:metabolism; D019731:Carbon-Nitrogen Ligases / Q000145:classification / Q000235:genetics* / Q000378:metabolism; D002736:Chloroplasts / Q000378:metabolism; D057075:Enzyme Assays; D005492:Folic Acid / Q000378:metabolism; D017353:Gene Deletion; D023281:Genomics; D019622:Haloferax volcanii / Q000201:enzymology / Q000235:genetics* / Q000254:growth & development; D008969:Molecular Sequence Data; D005810:Multigene Family; D010802:Phylogeny; D017434:Protein Structure, Tertiary; D021381:Protein Transport; D013831:Thiamine / Q000378:metabolism*
chemical_list: D029681:Arabidopsis Proteins; D001426:Bacterial Proteins; D005492:Folic Acid; D019731:Carbon-Nitrogen Ligases; C021557:5,10-methenyltetrahydrofolate synthetase; D013831:Thiamine