The 380 kb pCMU01 Plasmid Encodes Chloromethane Utilization Genes and Redundant Genes for Vitamin B12- and Tetrahydrofolate-Dependent Chloromethane Metabolism in Methylobacterium extorquens CM4: A Proteomic and Bioinformatics Study
Figure 1
Methylotrophic metabolism and chloromethane utilization pathway in Methylobacterium extorquens CM4.
The left-hand scale indicates carbon oxidation state. The chloromethane utilization cmu pathway (bold arrows) funnels the chloromethane-derived methyl group into central metabolism via methylene-H4F (CH2 = H4F), while the methanol (CH3OH) oxidation pathway operates with formaldehyde (HCHO) as a metabolic intermediate (grey arrows). H4F- and H4MPT-dependent enzyme-mediated steps are depicted in blue and pink, respectively. Carbon assimilation operates via the serine cycle (Ser) coupled with the ethylmalonyl-CoA pathway (EMCP) [67]. Spontaneous condensation of HCHO with H4F or H4MPT, and formaldehyde oxidation to methylene-H4F are shown with broken line. In the cmu pathway, the methyl group enters a specific H4F-oxidation pathway for energy production driven by the FolD and PurU enzymes. Protein-encoded genes or genes located on plasmid pCMU01 are shown in bold. Boxes and circles highlight proteins more abundant in chloromethane- and methanol grown-cultures, respectively. CmuA, methyltransferase/corrinoid-binding two-domain protein; CmuB, methylcobalamin:H4F methyltransferase; Fae, formaldehyde activating enzyme; Fch, methenyl-H4F cyclohydrolase; FDHs, formate dehydrogenases; Fhc, formyltransferase-hydrolase complex; FolD, bifunctional methylene-H4F dehydrogenase/cyclohydrolase; FtfL, formate-H4F ligase; Gck, glycerate kinase; GcvT, H4F-dependent aminomethyltransferase; HprA, hydroxypyruvate reductase; MDH, methanol dehydrogenase; MetF, methylene-H4F reductase; MtdA, bifunctional NAD(P)-dependant methylene-H4F and methylene-H4MPT dehydrogenase; MtdB, NAD(P)-dependent methylene-H4MPT dehydrogenase; Mch, methenyl-H4MPT cyclohydrolase; MtkA, malate thiokinase large subunit; MxaF, MDH alpha subunit, PurU, 10-formyl-H4F hydrolase; Sga, serine-glyoxylate aminotransferase [12]. Plasmid pCMU01 encoded proteins with predicted functions include putative uncharacterized methyltransferases CmuC and CmuC2, the putative PaaE-like oxidoreductase, and the putative PQQ-linked dehydrogenase of unknown specificity XoxF2. GvcT may serve to transfer methyl groups from a wide range of substrates to H4F, as proposed for members that belong to the COG0354-related enzymes such as YgfZ [68].