InterPro domain: IPR020831

This entry contains a small clade of dehydrogenases in gamma-proteobacteria which utilise NAD+ to oxidize erythrose-4-phosphate (E4P) to 4-phospho-erythronate, a precursor for the de novo synthesis of pyridoxine via 4-hydroxythreonine and D-1-deoxyxylulose [ 1 ]. This enzyme activity appears to have evolved from glyceraldehyde-3-phosphate dehydrogenase, whose substrate differs only in the lack of one carbon relative to E4P. It is possible that some of the GAPDH enzymes may prove to be bifunctional in certain species.

Glyceraldehyde-3-phosphate dehydrogenase (GAPDH) plays an important role in glycolysis and gluconeogenesis [ 2 ] by reversibly catalysing the oxidation and phosphorylation of D-glyceraldehyde-3-phosphate to 1,3-diphospho-glycerate. The enzyme exists as a tetramer of identical subunits, each containing 2 conserved functional domains: an NAD-binding domain, and a highly conserved catalytic domain [ 3 ]. The enzyme has been found to bind to actin and tropomyosin, and may thus have a role in cytoskeleton assembly. Alternatively, the cytoskeleton may provide a framework for precise positioning of the glycolytic enzymes, thus permitting efficient passage of metabolites from enzyme to enzyme [ 4 ].

GAPDH displays diverse non-glycolytic functions as well, its role depending upon its subcellular location. For instance, the translocation of GAPDH to the nucleus acts as a signalling mechanism for programmed cell death, or apoptosis [ 4 ]. The accumulation of GAPDH within the nucleus is involved in the induction of apoptosis, where GAPDH functions in the activation of transcription. The presence of GAPDH is associated with the synthesis of pro-apoptotic proteins like BAX, c-JUN and GAPDH itself.

GAPDH has been implicated in certain neurological diseases: GAPDH is able to bind to the gene products from neurodegenerative disorders such as Huntington's disease, Alzheimer's disease, Parkinson's disease and Machado-Joseph disease through stretches encoded by their CAG repeats. Abnormal neuronal apoptosis is associated with these diseases. Propargylamines such as deprenyl increase neuronal survival by interfering with apoptosis signalling pathways via their binding to GAPDH, which decreases the synthesis of pro-apoptotic proteins [ 5 ].

1. Biochemical characterization of gapB-encoded erythrose 4-phosphate dehydrogenase of Escherichia coli K-12 and its possible role in pyridoxal 5'-phosphate biosynthesis. J. Bacteriol. 177, 2804-12
2. Genomic organization of the glyceraldehyde-3-phosphate dehydrogenase gene family of Caenorhabditis elegans. J. Mol. Biol. 206, 411-24
3. Cloning and sequencing of a deoxyribonucleic acid copy of glyceraldehyde-3-phosphate dehydrogenase messenger ribonucleic acid isolated from chicken muscle. Biochemistry 22, 1605-13
4. Glyceraldehyde-3-phosphate dehydrogenase and apoptosis. null 60, 150-4
5. Neuroprotection by deprenyl and other propargylamines: glyceraldehyde-3-phosphate dehydrogenase rather than monoamine oxidase B. J. Neurosci. Res. 110, 509-15