FolB

Dihydroneopterin aldolase
FolB
SMART accession number:SM00905
Description: Dihydroneopterin aldolase catalyses the conversion of 7,8-dihydroneopterin to 6-hydroxymethyl-7,8-dihydropterin in the biosynthetic pathway of tetrahydrofolate. In the opportunistic pathogen Pneumocystis carinii, dihydroneopterin aldolase function is expressed as the N-terminal portion of the multifunctional folic acid synthesis protein (Fas). This region encompasses two domains, FasA and FasB, which are 27% amino acid identical. FasA and FasB also share significant amino acid sequence similarity with bacterial dihydroneopterin aldolases. This region consists of two tandem sequences each homologous to folB and which form tetramers (PUBMED:9709001).
Interpro abstract (IPR006157):

Dihydroneopterin aldolase (DHNA or folB) catalyses the conversion of 7,8-dihydroneopterin to 6-hydroxymethyl-7,8-dihydropterin in the biosynthetic pathway of tetrahydrofolate [(PUBMED:12039964)]. Folate derivatives are essential cofactors in the biosynthesis of purines, pyrimidines, and amino acids, as well as formyl-tRNA. Mammalian cells are able to utilize pre-formed folates after uptake by a carrier-mediated active transport system. Most microbes and plants lack this system and must synthesize folates de novo from guanosine triphosphate and DHNA is one enzyme in this pathway. In the opportunistic pathogen Pneumocystis carinii, dihydroneopterin aldolase function is expressed as the N-terminal portion of the multifunctional folic acid synthesis protein (Fas). This region encompasses two domains, FasA and FasB, which are 27% amino acid identical [(PUBMED:9709001)]. FasA and FasB also share significant amino acid sequence similarity with bacterial dihydroneopterin aldolases.

This entry also includes 7,8-dihydroneopterin triphosphate epimerase domain (DHNTPE or folX). Though it is known that DHNTPE catalyzes the epimerization of dihydroneopterin triphosphate to dihydromonapterin triphosphate, the biological role of this enzyme is still unclear. It is hypothesized that it is not an essential protein since a folX knockout in E. coli has a normal phenotype and the fact that folX is not present in H. influenza [(PUBMED:9182560),(PUBMED:9006053)]. DHNA and DHNTPE have been shown to be able to compensate for the other's activity albeit at slower reaction rates [(PUBMED:9651328)]. The functional enzyme for both is an octamer of identical subunits. Mammals lack many of the enzymes in the folate pathway including, DHNA and DHNTPE.

This region consists of two tandem sequences each homologous to folB and which form tetramers [(PUBMED:10737935)].

GO process:folic acid-containing compound metabolic process (GO:0006760)
GO function:dihydroneopterin aldolase activity (GO:0004150)
Family alignment:
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There are 18261 FolB domains in 17999 proteins in SMART's nrdb database.

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