Characterization of the formyltransferase from Methylobacterium extorquens AM1

Abstract

Methylobacterium extorquens AM1 possesses a formaldehyde-oxidation pathway that involves enzymes with high sequence identity with enzymes from methanogenic and sulfate-reducing archaea. Here we describe the purification and characterization of formylmethanofuran -tetrahydromethanopterin formyltransferase (Ftr), which catalyzes the reversible formation of formylmethanofuran (formylMFR) and tetrahydromethanopterin (H 4 MPT) from N 5 -formylH 4-MPT and methanofuran (MFR). Formyltransferase from M. extorquens AM1 showed activity with MFR and H 4 MPT isolated from the methanogenic archaeon Methanothermobacter marburgensis (apparent K m for formylMFR ¼ 50 mM; apparent K m for H 4 MPT ¼ 30 mM). The enzyme is encoded by the ffsA gene and exhibits a sequence identity of < 40% with Ftr from methanogenic and sulfate-reducing archaea. The 32-kDa Ftr protein from M. extorquens AM1 copurified in a complex with three other polypeptides of 60 kDa, 37 kDa and 29 kDa. Interestingly, these are encoded by the genes orf1, orf2 and orf3 which show sequence identity with the formylMFR dehydrogenase subunits FmdA, FmdB and FmdC, respectively. The clustering of the genes orf2, orf1, ffsA, and orf3 in the chromosome of M. extorquens AM1 indicates that, in the bacterium, the respective polypeptides form a functional unit. Expression studies in Escherichia coli indicate that Ftr requires the other subunits of the complex for stability. Despite the fact that three of the polypeptides of the complex showed sequence similarity to subunits of Fmd from methanogens, the complex was not found to catalyze the oxidation of formylMFR. Detailed comparison of the primary structure revealed that Orf2, the homolog of the active site harboring subunit FmdB, lacks the binding motifs for the activesite cofactors molybdenum, molybdopterin and a [4Fe24S] cluster. Cytochrome c was found to be spontaneously reduced by H 4 MPT. On the basis of this property, a novel assay for Ftr activity and MFR is described.Keywords: C1 metabolism; methanofuran; methanogenic archaea; methylotrophic bacteria; tetrahydromethanopterin.Oxidation of formaldehyde to CO 2 in Methylobacterium extorquens AM1 was recently found to involve tetrahydromethanopterin (H 4 MPT) and a methanofuran (MFR) analog, coenzymes previously thought to be present only in methanogenic and sulfate-reducing archaea. The following enzymes have been proposed to participate in the metabolic pathway: formaldehyde-activating enzyme (Fae) [1], methyleneH 4 MPT dehydrogenases (MtdA and MtdB) [2,3], and three enzymes with high sequence identity with enzymes involved in methanogenesis: methenylH 4 MPT cyclohydrolase (Mch), formylMFR-H 4 MPT formyltransferase (Ftr), and formylMFR dehydrogenase (Fmd) [4] (Fig. 1).Of these enzymes, Fae, Mtd and Mch have been purified and characterized from M. extorquens AM1 [1 -3,5].In M. extorquens AM1, the genes for Mch, MtdB, and Fae are located in a single gene cluster [4]. This cluster also contains genes encoding polypeptides with sequence identity with Ftr and Fmd subunits (Fi...

Dichloromethane metabolism and C1 utilization genes in Methylobacterium strains The GenBank accession numbers for the sequences determined in this work are AJ421476 and AJ421477.

“…As proposed by Chistoserdova et al (1998), cytoplasmic formaldehyde reacts with either H 4 folate or H 4 MPT, and the C 1 unit is further oxidized to CO 2 or incorporated into cell biomass via the serine cycle. Fae, formaldehyde-activating enzyme ; MtdA, methylene H 4 folate/H 4 MPT dehydrogenase (Vorholt et al, 1998 ;Hagemeier et al, 2001) ; MtdB, methylene H 4 MPT dehydrogenase (Hagemeier et al, 2000) ; FchA, methenyl-H 4 folate cyclohydrolase ; MchA, methenyl-H 4 MPT cyclohydrolase (Pomper et al, 1999) ; fts, formyl-H 4 folate synthase ; Ftr, formylmethanofuran H 4 MPT formyltransferase encoded by ffsA, which is in complex with the gene products of orf123 (Pomper & Vorholt, 2001) ; fdh, formate dehydrogenase. Dotted arrows denote steps that are as yet poorly characterized.…”

Formaldehyde-Detoxifying Role of theTetrahydromethanopterin-Linked Pathway in Methylobacteriumextorquens AM1

“…Methenyl-H 4 MPT is converted to formyl-H 4 MPT by methenyl-H 4 MPT cyclohydrolase (Mch) (24). Finally, formate is released from formyl-H 4 MPT through the action of the formyltransferase/hydrolase complex (Fhc) (22,23). Formate can then be oxidized to CO 2 by formate dehydrogenase, as for the H 4 F-linked pathway.…”

“…Formate can then be oxidized to CO 2 by formate dehydrogenase, as for the H 4 F-linked pathway. Fhc contains formyltransferase activity that is active with methanofuran purified from the methanogen Methanothermobacter marburgensis (23). The identity and function of the methanofuran analog present in M. extorquens AM1 has not yet been determined, however, and so this pathway simply will be referred to here as the H 4 MPT pathway.…”

Purification of the Formate-Tetrahydrofolate Ligasefrom Methylobacterium extorquens AM1 and Demonstrationof Its Requirement for MethylotrophicGrowth

“…The reaction of formaldehyde with H 4 MPT, a folate analogue that had long been thought to be unique to methanogenic archaea (9), can occur either spontaneously or through the action of the formaldehyde-activating enzyme, Fae (42). Methylene-H 4 MPT is subsequently oxidized to methenyl-H 4 MPT and then formyl-H 4 MPT (14,34,40), which is ultimately hydrolyzed by the formyltransferase/hydrolase complex, Fhc, to produce formate and free H 4 MPT (32,33). Mutants defective for the H 4 MPT pathway fail to grow on C 1 substrates and are sensitive to the presence of compounds that lead to the production of formaldehyde (14,27,30,42).…”