Disease relevance of PPAT

• The human gene localizes to chromosome 17q12-21 and contains regions with sequence similarity to the monofunctional Escherichia coli DPCK and PPAT [1].
• This review focuses on the potential of glycerol-3-phosphate acyltransferase (GPAT) inhibition as a strategy to treat insulin resistance, one of the characteristics of obesity and type 2 diabetes [2].
• We have developed two serological tests, ELISA and GPAT, to demonstrate Strongyloides infection and possible applications of the serological tests for diagnosis, mass-screening, epidemiological study and postchemotherapy evaluation of strongyloidiasis were reviewed based on our recent studies [3].

High impact information on PPAT

• The three-dimensional structures of tryptophan synthase, carbamoyl phosphate synthetase, glutamine phosphoribosylpyrophosphate amidotransferase, and asparagine synthetase have revealed the relative locations of multiple active sites within these proteins [4].
• Acyl-CoA:glycerol-3-phosphate acyltransferase (GPAT) catalyzes the first step during de novo synthesis of triacylglycerol [5].
• Although the mitochondrial-associated GPAT has been cloned and extensively characterized, the molecular identity of the endoplasmic reticulum (ER)-associated GPAT, which accounts for the majority of total GPAT activity in most tissues, has remained elusive [5].
• Ectopic expression of GPAT3 leads to a significant increase in N-ethylmaleimide-sensitive GPAT activity, whereas acyltransferase activity toward a variety of other lysophospholipids, as well as neutral lipid substrates, is not altered [5].
• A substantial loss of GPAT activity in 3T3-L1 adipocytes was achieved by reducing GPAT3 mRNA levels through GPAT3-specific siRNA knockdown [5].

Biological context of PPAT

• The GPAT gene was mapped to the q12 region of chromosome 4 [6].
• GPAT and AIRC are closely linked and divergently transcribed from an intergenic region of approximately 625 base pairs [6].
• The human GPAT and AIRC genes are divergently transcribed from a 558 bp intergenic promoter region [7].
• Here, we describe the analysis in P. falciparum of the first step of phospholipid biosynthesis that controls acylation of glycerol 3-phosphate (GPAT) at the sn-1 position [8].
• This study, which describes the first protozoan GPAT gene, reveals an important role for the endoplasmic reticulum in the initial step of Plasmodium membrane biogenesis [8].

Anatomical context of PPAT

• Confocal microscopy of CHO and HEK293 cells transfected with the GPAT-FLAG construct showed that GPAT was located correctly in mitochondria and was not present elsewhere in the cell [9].
• To test this hypothesis, we overexpressed mitochondrial GPAT in Chinese hamster ovary (CHO) cells [9].
• Reduced plasma FFA availability increases net triacylglycerol degradation, but not GPAT or HSL activity, in human skeletal muscle [10].
• We showed, for the first time, that anti-CD3 stimulation in rat splenic T-lymphocytes selectively increased mitochondrial glycerol-3-phosphate acyltransferase (GPAT) activity [11].
• The enzyme in chloroplasts is soluble and uses acyl-(acyl-carrier protein) as the acyl donor, whereas the enzymes in the mitochondria and the cytoplasm are bound to membranes and use acyl-CoA as the acyl donor. cDNAs for GPAT of chloroplasts have been cloned from several plants, and the gene for the enzyme has been cloned from Arabidopsis thaliana [12].

Associations of PPAT with chemical compounds

• In an effort to overcome this limitation, truncated derivatives of 1 were designed, synthesized and tested as p300HAT inhibitors as well as substrates for the CoA biosynthetic bifunctional enzyme phosphopantetheine adenylyltransferase-dephospho-CoA kinase (PPAT/DPCK) [13].
• Tryptamine phosphopantetheine (3) is converted to tryptamine-coenzyme A (CoA) bisubstrate analog (1) by human phosphoribosyl pyrophosphate amidotransferase (PPAT) and dephosphocoenzyme A kinase (DPCK) in vitro [14].
• A cDNA encoding human glutamine phosphoribosylpyrophosphate amidotransferase for step one in de novo purine nucleotide synthesis was cloned, sequenced, and expressed in Chinese hamster ovary cells to yield functional enzyme [6].
• In GPAT-overexpressing cells, the incorporation of label into phospholipid, particularly phosphatidylcholine, decreased 30%, despite normal growth rate and phospholipid content, suggesting that exogenous oleate was directed primarily toward triacylglycerol synthesis [9].
• A stable carbocyclic analog of 5-phosphoribosyl-1-pyrophosphate to probe the mechanism of catalysis and regulation of glutamine phosphoribosylpyrophosphate amidotransferase [15].

Other interactions of PPAT

• The human genes GPAT, encoding the amidotransferase, and AIRC, encoding a bifunctional enzyme for steps six and seven in the pathway, were cloned and characterized [6].
• Role of NRF-1 in bidirectional transcription of the human GPAT-AIRC purine biosynthesis locus [7].
• Cys-1 and Asp-33 are cognate to residues Cys-1 and Asp-29 in glutamine phosphoribosylpyrophosphate amidotransferase which have been proposed to be members of a catalytic triad responsible for mediating nitrogen transfer in this enzyme (Mei, B., and Zalkin, H. (1989) J. Biol. Chem. 264, 16613-16619) [16].

Analytical, diagnostic and therapeutic context of PPAT

• Genetic engineering of the unsaturation of fatty acids has been achieved by manipulation of the cDNA for the GPAT found in chloroplasts and has allowed modification of the ability of tobacco to tolerate chilling temperatures [12].

References