Antiporter that mediates the import of reduced folates or a subset of cyclic dinucleotides, driven by the export of organic anions (PubMed:10787414, PubMed:15337749, PubMed:16115875, PubMed:22554803, PubMed:31126740, PubMed:31511694, PubMed:32276275, PubMed:36071163, PubMed:36265513, PubMed:36575193, PubMed:7826387, PubMed:9041240). Acts as an importer of immunoreactive cyclic dinucleotides, such as cyclic GMP-AMP (2'-3'-cGAMP), an immune messenger produced in response to DNA virus in the cytoso

Cell membraneApical cell membraneBasolateral cell membrane

Megaloblastic anemia, folate-responsive

An autosomal recessive metabolic disorder characterized by megaloblastic anemia resulting from decreased folate transport into erythrocytes. Disease manifestations include hemolytic anemia, hyperhomocysteinemia, and low vitamin B12. Serum folate levels are normal, but erythrocyte folate levels are decreased. Treatment with oral folate corrects the anemia and normalizes homocysteine.

Mediates high affinity thiamine uptake, probably via a proton anti-port mechanism (PubMed:11731220, PubMed:33008889, PubMed:35512554, PubMed:35724964). Has no folate transport activity (PubMed:11731220). Mediates H(+)-dependent pyridoxine transport (PubMed:33008889, PubMed:35512554, PubMed:35724964, PubMed:36456177)

Membrane

Basal ganglia disease, biotin-thiamine responsive

An autosomal recessive metabolic disorder characterized by episodic encephalopathy, often triggered by febrile illness, presenting as confusion, seizures, external ophthalmoplegia, dysphagia, and sometimes coma and death. If untreated, encephalopathies can result in permanent dystonia. Brain imaging may show characteristic bilateral lesions of the basal ganglia.

Mitochondrial transporter mediating uptake of thiamine diphosphate into mitochondria. It is not clear if the antiporter activity is affected by the membrane potential or by the proton electrochemical gradient

Mitochondrion membrane

Microcephaly, Amish type

A disorder characterized by severe congenital microcephaly and severe 2-ketoglutaric aciduria leading to death within the first year.

Catalyzes the reduction of 7,8-dihydrofolate (DHF) to 5,6,7,8-tetrahydrofolate in a NADPH-dependent manner (PubMed:12096917, PubMed:15039552, PubMed:17569517, PubMed:19196009, PubMed:19478082, PubMed:21876184, PubMed:9719595). Key enzyme in folate metabolism. Contributes to the nuclear and mitochondrial de novo thymidylate biosynthesis pathway (PubMed:21876188, PubMed:22235121). Catalyzes an essential reaction for de novo glycine and purine synthesis, and for DNA precursor synthesis. Binds its o

MitochondrionCytoplasmNucleus

Megaloblastic anemia due to dihydrofolate reductase deficiency

An inborn error of metabolism, characterized by megaloblastic anemia and/or pancytopenia, severe cerebral folate deficiency, and cerebral tetrahydrobiopterin deficiency. Clinical features include variable neurologic symptoms, ranging from severe developmental delay and generalized seizures in infancy, to childhood absence epilepsy with learning difficulties, to lack of symptoms.

Transcription factor, which has both transcriptional activation and repression activities (PubMed:31905202). Also modulates chromatin accessibility (PubMed:38361031). In complex with HCFC1 and ZNF143, regulates the expression of several genes, including AP2S1, ESCO2, OPHN1, RBL1, UBXN8 and ZNF32 (PubMed:26416877). May regulate the expression of genes that encode both cytoplasmic and mitochondrial ribosomal proteins (By similarity). Required for normal mitochondrial development and function. Regu

NucleusCytoplasm

Methylmalonic aciduria and homocystinuria type cblL

An autosomal recessive disorder of cobalamin metabolism clinically characterized by early-onset seizures, and profound global developmental delay with severe intellectual disability. Metabolic features are mild methylmalonic aciduria, low-normal plasma methionine, and high-normal plasma homocysteine.

Proton-coupled folate symporter that mediates folate absorption using an H(+) gradient as a driving force (PubMed:17129779, PubMed:17446347, PubMed:17475902, PubMed:19389703, PubMed:19762432, PubMed:25504888, PubMed:29344585, PubMed:30858177, PubMed:31494288, PubMed:31792273, PubMed:32893190, PubMed:34619546). Involved in the intestinal absorption of folates at the brush-border membrane of the proximal jejunum, and the transport from blood to cerebrospinal fluid across the choroid plexus (PubMed

Cell membraneApical cell membraneBasolateral cell membraneEndosome membraneCytoplasm

Hereditary folate malabsorption

Rare autosomal recessive disorder characterized by impaired intestinal folate absorption with folate deficiency resulting in anemia, hypoimmunoglobulinemia with recurrent infections, and recurrent or chronic diarrhea. In many patients, neurological abnormalities such as seizures or intellectual disability become apparent during early childhood, attributed to impaired transport of folates into the central nervous system. When diagnosed early, the disorder can be treated by administration of folate. If untreated, it can be fatal and, if treatment is delayed, the neurological defects can become permanent.

Involved in cobalamin metabolism and trafficking (PubMed:18385497, PubMed:23415655, PubMed:24722857, PubMed:26364851). Plays a role in regulating the biosynthesis and the proportion of two coenzymes, methylcob(III)alamin (MeCbl) and 5'-deoxyadenosylcobalamin (AdoCbl) (PubMed:18385497, PubMed:23415655, PubMed:24722857). Promotes oxidation of cob(II)alamin bound to MMACHC (PubMed:26364851). The processing of cobalamin in the cytosol occurs in a multiprotein complex composed of at least MMACHC, MMA

CytoplasmMitochondrion

Methylmalonic aciduria and homocystinuria, cblD type

An autosomal recessive disorder of cobalamin metabolism characterized by decreased levels of the coenzymes adenosylcobalamin (AdoCbl) and methylcobalamin (MeCbl). Clinical features include developmental delay, hyotonia, intellectual disability, seizures, and megaloblastic anemia. Laboratory studies show methylmalonic aciduria and homocystinuria.

Catalyzes the conversion of 5,10-methylenetetrahydrofolate to 5-methyltetrahydrofolate, a cosubstrate for homocysteine remethylation to methionine (PubMed:29891918). Represents a key regulatory connection between the folate and methionine cycles (Probable)

Homocystinuria due to deficiency of N(5,10)-methylenetetrahydrofolate reductase activity

An autosomal recessive inborn error of folate metabolism. Clinical severity is variable, ranging from severe neurologic features to absence of symptoms. Clinical features include homocysteinuria, homocysteinemia, developmental delay, severe intellectual disability, perinatal death, psychiatric disturbances, and later-onset neurodegenerative disorders.

Contributes to tetrahydrofolate metabolism. Helps regulate carbon flow through the folate-dependent one-carbon metabolic network that supplies carbon for the biosynthesis of purines, thymidine and amino acids. Catalyzes the irreversible conversion of 5-formyltetrahydrofolate (5-FTHF) to yield 5,10-methenyltetrahydrofolate

Cytoplasm

Neurodevelopmental disorder with microcephaly, epilepsy, and hypomyelination

An autosomal recessive neurodevelopmental disorder with onset at birth or in early infancy, and characterized by microcephaly, short stature, severe global developmental delay, progressive spasticity, and epilepsy. Brain imaging shows delayed myelination, hypomyelination, enlarged ventricles, and cerebellar atrophy.

Cobalamin (vitamin B12) cytosolic chaperone that catalyzes the reductive decyanation of cyanocob(III)alamin (cyanocobalamin, CNCbl) to yield cob(II)alamin and cyanide, using FAD or FMN as cofactors and NADPH as cosubstrate (PubMed:18779575, PubMed:19700356, PubMed:21697092, PubMed:25809485). Cyanocobalamin constitutes the inactive form of vitamin B12 introduced from the diet, and is converted into the active cofactors methylcobalamin (MeCbl) involved in methionine biosynthesis, and 5'-deoxyadeno

Cytoplasm, cytosol

Methylmalonic aciduria and homocystinuria, cblC type

An autosomal recessive disorder of cobalamin metabolism characterized by decreased levels of the coenzymes adenosylcobalamin (AdoCbl) and methylcobalamin (MeCbl). Affected individuals may have developmental, hematologic, neurologic, metabolic, ophthalmologic, and dermatologic clinical findings. Although considered a disease of infancy or childhood, some individuals develop symptoms in adulthood.

Primary vitamin B12-binding and transport protein. Delivers cobalamin to cells

Secreted

Transcobalamin II deficiency

An autosomal recessive disorder manifesting in early infancy and characterized by failure to thrive, megaloblastic anemia, pancytopenia, and agammaglobulinemia. Additional features include methylmalonic aciduria, recurrent infections, vomiting and diarrhea. TCN2D may be accompanied by neurological complications, including psychomotor and mental developmental delay, if untreated.

Receptor for transcobalamin saturated with cobalamin (TCbl) (PubMed:18779389). Plays an important role in cobalamin uptake (PubMed:18779389, PubMed:20524213). Plasma membrane protein that is expressed on follicular dendritic cells (FDC) and mediates interaction with germinal center B cells (PubMed:10727470). Functions as costimulator to promote B cell responses to antigenic stimuli; promotes B cell differentiation and proliferation (PubMed:10727470, PubMed:11418631). Germinal center-B (GC-B) cel

Cell membrane

Methylmalonic aciduria, transient, due to transcobalamin receptor defect

An autosomal recessive metabolic condition characterized by moderate methymalonicaciduria, and normal plasma vitamin B12 levels. Serum homocysteine may be increased in some affected individuals. Most cases are clinically asymptomatic.

Lysosomal membrane protein that transports cobalamin (Vitamin B12) from the lysosomal lumen to the cytosol in an ATP-dependent manner (PubMed:22922874, PubMed:28572511, PubMed:31467407, PubMed:33845046). Targeted by LMBRD1 lysosomal chaperone from the endoplasmic reticulum to the lysosomal membrane (PubMed:27456980). Then forms a complex with lysosomal chaperone LMBRD1 and cytosolic MMACHC to transport cobalamin across the lysosomal membrane (PubMed:25535791)

Endoplasmic reticulum membraneLysosome membrane

Methylmalonic aciduria and homocystinuria type cblJ

A disorder of cobalamin metabolism characterized by decreased levels of the coenzymes adenosylcobalamin (AdoCbl) and methylcobalamin (MeCbl). Clinical features include feeding difficulties, poor growth, hypotonia, lethargy, anemia, and developmental delay.

High-affinity transporter for the intake of thiamine (PubMed:10391222, PubMed:10542220, PubMed:21836059, PubMed:33008889, PubMed:35512554, PubMed:35724964). Mediates H(+)-dependent pyridoxine transport (PubMed:33008889, PubMed:35512554, PubMed:35724964)

Cell membrane

Thiamine-responsive megaloblastic anemia syndrome

An autosomal recessive disease characterized by megaloblastic anemia, diabetes mellitus, and sensorineural deafness. Onset is typically between infancy and adolescence, but all of the cardinal findings are often not present initially. The anemia, and sometimes the diabetes, improves with high doses of thiamine. Other more variable features include optic atrophy, congenital heart defects, short stature, and stroke.

Catalyzes the transfer of a methyl group from methylcob(III)alamin (MeCbl) to homocysteine, yielding enzyme-bound cob(I)alamin and methionine in the cytosol (PubMed:16769880, PubMed:17288554, PubMed:27771510). MeCbl is an active form of cobalamin (vitamin B12) used as a cofactor for methionine biosynthesis. Cob(I)alamin form is regenerated to MeCbl by a transfer of a methyl group from 5-methyltetrahydrofolate (PubMed:16769880, PubMed:17288554, PubMed:27771510). The processing of cobalamin in the

Cytoplasm

Homocystinuria-megaloblastic anemia, cblG type

An autosomal recessive inborn error of metabolism resulting from defects in the cobalamin-dependent pathway that converts homocysteine to methionine. It causes delayed psychomotor development, megaloblastic anemia, homocystinuria, and hypomethioninemia.

Converts cob(I)alamin to adenosylcobalamin (adenosylcob(III)alamin), a coenzyme for methylmalonyl-CoA mutase, therefore participates in the final step of the vitamin B12 conversion (PubMed:12514191). Generates adenosylcobalamin (AdoCbl) and directly delivers the cofactor to MUT in a transfer that is stimulated by ATP-binding to MMAB and gated by MMAA (Probable)

Mitochondrion

Methylmalonic aciduria, cblB type

An autosomal recessive disorder of methylmalonate and cobalamin metabolism due to defective synthesis of adenosylcobalamin.

Membrane

Symmetrically cleaves beta-carotene into two molecules of retinal using a dioxygenase mechanism

Cytoplasm, cytosol

Hypercarotenemia and vitamin A deficiency, autosomal dominant

A disorder characterized by increased serum beta-carotene, decreased conversion of beta-carotene to vitamin A and decreased serum vitamin A.

Thiol-specific peroxidase that catalyzes the reduction of hydrogen peroxide and organic hydroperoxides to water and alcohols, respectively. Plays a role in cell protection against oxidative stress by detoxifying peroxides and as sensor of hydrogen peroxide-mediated signaling events. Might participate in the signaling cascades of growth factors and tumor necrosis factor-alpha by regulating the intracellular concentrations of H(2)O(2) (PubMed:9497357). Reduces an intramolecular disulfide bond in G

CytoplasmMelanosome

Binds to folate and reduced folic acid derivatives and mediates delivery of 5-methyltetrahydrofolate and folate analogs into the interior of cells (PubMed:19074442, PubMed:23851396, PubMed:23934049, PubMed:2527252, PubMed:8033114, PubMed:8567728). Has high affinity for folate and folic acid analogs at neutral pH (PubMed:23851396, PubMed:23934049, PubMed:2527252, PubMed:8033114, PubMed:8567728). Exposure to slightly acidic pH after receptor endocytosis triggers a conformation change that strongly

Cell membraneApical cell membraneBasolateral cell membraneSecretedCytoplasmic vesicleCytoplasmic vesicle, clathrin-coated vesicleEndosome

Neurodegeneration due to cerebral folate transport deficiency

An autosomal recessive neurodegenerative disorder resulting from brain-specific folate deficiency early in life. Onset is apparent in late infancy with severe developmental regression, movement disturbances, epilepsy and leukodystrophy.

Key enzyme in methionine and folate homeostasis responsible for the reactivation of methionine synthase (MTR/MS) activity by catalyzing the reductive methylation of MTR-bound cob(II)alamin (PubMed:17892308). Cobalamin (vitamin B12) forms a complex with MTR to serve as an intermediary in methyl transfer reactions that cycles between MTR-bound methylcob(III)alamin and MTR bound-cob(I)alamin forms, and occasional oxidative escape of the cob(I)alamin intermediate during the catalytic cycle leads to

Cytoplasm

Homocystinuria-megaloblastic anemia, cblE type

An autosomal recessive inborn error of metabolism resulting from defects in the cobalamin-dependent pathway that converts homocysteine to methionine. It causes delayed psychomotor development, megaloblastic anemia, homocystinuria, and hypomethioninemia. Cells from patients with HMAE fail to incorporate methyltetrahydrofolate into methionine in whole cells, but cell extracts show normal methionine synthase activity in the presence of a reducing agent.

Transcriptional coregulator (By similarity). Serves as a scaffold protein, bridging interactions between transcription factors, including THAP11 and ZNF143, and transcriptional coregulators (PubMed:26416877). Involved in control of the cell cycle (PubMed:10629049, PubMed:10779346, PubMed:15190068, PubMed:16624878, PubMed:23629655). Also antagonizes transactivation by ZBTB17 and GABP2; represses ZBTB17 activation of the p15(INK4b) promoter and inhibits its ability to recruit p300 (PubMed:10675337

CytoplasmNucleus

Methylmalonic aciduria and homocystinuria, cblX type

An X-linked recessive metabolic disorder characterized by severely delayed psychomotor development apparent in infancy, failure to thrive, impaired intellectual development, and intractable epilepsy. Additional features may include microcephaly and choreoathetosis.

Catalyzes the phosphorylation of thiamine to thiamine pyrophosphate (TPP) utilizing UTP and therefore links the biosynthesis of TPP to pyrimidines metabolism (PubMed:38547260). By producing thiamine pyrophosphate, a cofactor of the mitochondrial pyruvate dehydrogenase indirectly regulates pyruvate oxidation and lipogenesis (PubMed:38547260). Although it can also catalyze thiamine phosphorylation using ATP and CTP in vitro, it does so with significantly lower efficiency and without physiological

Thiamine metabolism dysfunction syndrome 5, episodic encephalopathy type

An autosomal recessive metabolic disorder due to an inborn error of thiamine metabolism. The phenotype is highly variable, but in general, affected individuals have onset in early childhood of acute encephalopathic episodes associated with increased serum and CSF lactate. These episodes result in progressive neurologic dysfunction manifest as gait disturbances, ataxia, dystonia, and spasticity, which in some cases may result in loss of ability to walk. Cognitive function is usually preserved, although mildly delayed development has been reported. These episodes are usually associated with infection and metabolic decompensation. Some patients may have recovery of some neurologic deficits.

Endocytic receptor which plays a role in lipoprotein, vitamin and iron metabolism by facilitating their uptake (PubMed:10371504, PubMed:11606717, PubMed:11717447, PubMed:14576052, PubMed:9572993). Acts together with LRP2 to mediate endocytosis of high-density lipoproteins, GC, hemoglobin, ALB, TF and SCGB1A1. Acts together with AMN to mediate endocytosis of the CBLIF-cobalamin complex (PubMed:14576052, PubMed:9572993). Binds to ALB, MB, Kappa and lambda-light chains, TF, hemoglobin, GC, SCGB1A1,

Apical cell membraneCell membraneMembrane, coated pitEndosomeLysosome membrane

Imerslund-Grasbeck syndrome 1

A form of Imerslund-Grasbeck syndrome, a rare autosomal recessive disorder characterized by vitamin B12 deficiency commonly resulting in megaloblastic anemia, which is responsive to parenteral vitamin B12 therapy and appears in infancy or early childhood. Clinical manifestations include failure to thrive, infections and neurological damage. Mild proteinuria, with no signs of kidney disease, is present in about half of the patients.

Promotes absorption of the essential vitamin cobalamin (Cbl) in the ileum. After interaction with CUBN, the CBLIF-cobalamin complex is internalized via receptor-mediated endocytosis

Secreted

Hereditary intrinsic factor deficiency

Autosomal recessive disorder characterized by megaloblastic anemia.

Folate-dependent enzyme, that displays both transferase and deaminase activity. Serves to channel one-carbon units from formiminoglutamate to the folate pool Binds and promotes bundling of vimentin filaments originating from the Golgi

Cytoplasm, cytosolGolgi apparatusCytoplasm, cytoskeleton, microtubule organizing center, centrosome, centriole

Glutamate formiminotransferase deficiency

Autosomal recessive disorder. Features of a severe phenotype, include elevated levels of formiminoglutamate (FIGLU) in the urine in response to histidine administration, megaloblastic anemia, and intellectual disability. Features of a mild phenotype include high urinary excretion of FIGLU in the absence of histidine administration, mild developmental delay, and no hematological abnormalities.

Lysosomal membrane chaperone required to export cobalamin (vitamin B12) from the lysosome to the cytosol, allowing its conversion to cofactors (PubMed:19136951). Targets ABCD4 transporter from the endoplasmic reticulum to the lysosome (PubMed:27456980). Then forms a complex with lysosomal ABCD4 and cytoplasmic MMACHC to transport cobalamin across the lysosomal membrane (PubMed:25535791). Acts as an adapter protein which plays an important role in mediating and regulating the internalization of t

Endoplasmic reticulum membraneLysosome membraneCell membraneCytoplasmic vesicle, clathrin-coated vesicle

Methylmalonic aciduria and homocystinuria, cblF type

An autosomal recessive disorder of cobalamin metabolism characterized by decreased levels of the coenzymes adenosylcobalamin (AdoCbl) and methylcobalamin (MeCbl). It is due to accumulation of free cobalamin in lysosomes, thus hindering its conversion to cofactors. Clinical features include developmental delay, stomatitis, glossitis, seizures and methylmalonic aciduria responsive to vitamin B12.

Membrane-bound component of the endocytic receptor formed by AMN and CUBN (PubMed:14576052, PubMed:29402915, PubMed:30523278). Required for normal CUBN glycosylation and trafficking to the cell surface (PubMed:14576052, PubMed:29402915). The complex formed by AMN and CUBN is required for efficient absorption of vitamin B12 (PubMed:12590260, PubMed:14576052, PubMed:26040326). Required for normal CUBN-mediated protein transport in the kidney (Probable)

Apical cell membraneCell membraneEndosome membraneMembrane, coated pitSecreted

Imerslund-Grasbeck syndrome 2

A form of Imerslund-Grasbeck syndrome, a rare autosomal recessive disorder characterized by vitamin B12 deficiency commonly resulting in megaloblastic anemia, which is responsive to parenteral vitamin B12 therapy and appears in infancy or early childhood. Clinical manifestations include failure to thrive, infections and neurological damage. Mild proteinuria, with no signs of kidney disease, is present in about half of the patients.