5-Formyltetrahydrofolate Is an Inhibitory but Well Tolerated Metabolite in Arabidopsis Leaves

• Published in: The Journal of biological chemistry Vol. 280; no. 28; pp. 26137 - 26142
• Main Authors: Goyer, Aymeric, Collakova, Eva, de la Garza, Rocío Díaz, Quinlivan, Eoin P., Williamson, Jerry, Gregory, Jesse F., Shachar-Hill, Yair, Hanson, Andrew D.
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 15.07.2005; American Society for Biochemistry and Molecular Biology
• Subjects: Arabidopsis; Arabidopsis - metabolism; Carbon Dioxide - chemistry; Carbon Dioxide - metabolism; Carbon-Nitrogen Ligases - chemistry; Carbon-Nitrogen Ligases - metabolism; Catalysis; DNA, Bacterial - chemistry; Flowers - metabolism; Formate-Tetrahydrofolate Ligase - chemistry; Formate-Tetrahydrofolate Ligase - genetics; Formyltetrahydrofolates - chemistry; Glycine - chemistry; Glycine Hydroxymethyltransferase - chemistry; Hydrolysis; Leucovorin - analogs & derivatives; Leucovorin - chemistry; Leucovorin - metabolism; Leucovorin - pharmacology; Mitochondria - metabolism; Models, Biological; Models, Chemical; Models, Genetic; Mutagenesis, Site-Directed; Mutation; Phenotype; Photosynthesis; Plant Leaves - metabolism; Protein Isoforms; RNA - chemistry; Serine - chemistry; Temperature; Tetrahydrofolates - chemistry; Tetrahydrofolates - metabolism; Time Factors
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.M503106200

5-Formyltetrahydrofolate (5-CHO-THF) is formed via a second catalytic activity of serine hydroxymethyltransferase (SHMT) and strongly inhibits SHMT and other folate-dependent enzymes in vitro. The only enzyme known to metabolize 5-CHO-THF is 5-CHO-THF cycloligase (5-FCL), which catalyzes its conversion to 5,10-methenyltetrahydrofolate. Because 5-FCL is mitochondrial in plants and mitochondrial SHMT is central to photorespiration, we examined the impact of an insertional mutation in the Arabidopsis 5-FCL gene (At5g13050) under photorespiratory (30 and 370 μmol of CO2 mol–1) and non-photorespiratory (3200 μmol of CO2 mol–1) conditions. The mutation had only mild visible effects at 370 μmol of CO2 mol–1, reducing growth rate by ∼20% and delaying flowering by 1 week. However, the mutation doubled leaf 5-CHO-THF level under all conditions and, under photorespiratory conditions, quadrupled the pool of 10-formyl-/5,10-methenyltetrahydrofolates (which could not be distinguished analytically). At 370 μmol of CO2 mol–1, the mitochondrial 5-CHO-THF pool was 8-fold larger in the mutant and contained most of the 5-CHO-THF in the leaf. In contrast, the buildup of 10-formyl-/5,10-methenyltetrahydrofolates was extramitochondrial. In photorespiratory conditions, leaf glycine levels were up to 46-fold higher in the mutant than in the wild type. Furthermore, when leaves were supplied with 5-CHO-THF, glycine accumulated in both wild type and mutant. These data establish that 5-CHO-THF can inhibit SHMT in vivo and thereby influence glycine pool size. However, the near-normal growth of the mutant shows that even exceptionally high 5-CHO-THF levels do not much affect fluxes through SHMT or any other folate-dependent reaction, i.e. that 5-CHO-THF is well tolerated in plants.