Glucose-6-phosphate exchanger SLC37A4

SLC37A4
Identifiers
Aliases	SLC37A4, G6PT1, G6PT2, G6PT3, GSD1b, GSD1c, GSD1d, TRG-19, TRG19, PRO0685, solute carrier family 37 member 4, CDG2W
External IDs	OMIM: 602671; MGI: 1316650; HomoloGene: 37482; GeneCards: SLC37A4; OMA:SLC37A4 - orthologs
Gene location (Human) Chr. Chromosome 11 (human) Band 11q23.3 Start 119,024,114 bp End 119,030,906 bp
Gene location (Mouse) Chr. Chromosome 9 (mouse) Band 9|9 A5.2 Start 44,308,149 bp End 44,314,265 bp
RNA expression pattern Bgee Human Mouse (ortholog) Top expressed in right lobe of liver duodenum body of pancreas islet of Langerhans renal cortex human kidney mucosa of transverse colon gastrocnemius muscle rectum skeletal muscle tissue Top expressed in right kidney vastus lateralis muscle triceps brachii muscle proximal tubule human kidney muscle of thigh extensor digitorum longus muscle left lobe of liver sternocleidomastoid muscle tibialis anterior muscle More reference expression data BioGPS More reference expression data
Gene ontology Molecular function transporter activity glucose-6-phosphate transmembrane transporter activity glucose 6-phosphate:inorganic phosphate antiporter activity antiporter activity transmembrane transporter activity Cellular component integral component of membrane membrane integral component of endoplasmic reticulum membrane endoplasmic reticulum endoplasmic reticulum membrane Biological process glucose-6-phosphate transport phosphate ion transmembrane transport glucose metabolic process glucose homeostasis carbohydrate transport transmembrane transport gluconeogenesis transport Sources:Amigo / QuickGO
Orthologs Species Human Mouse Entrez 2542 14385 Ensembl ENSG00000137700 ENSG00000281500 ENSMUSG00000032114 UniProt O43826 n/a RefSeq (mRNA) NM_001467 NM_001164277 NM_001164278 NM_001164279 NM_001164280 NM_001293630 NM_001293631 NM_008063 NM_001357729 NM_001357730 NM_001378829 NM_001378830 NM_001378831 NM_001378832 NM_001378833 NM_001378834 RefSeq (protein) NP_001157749 NP_001157750 NP_001157751 NP_001157752 NP_001458 n/a Location (UCSC) Chr 11: 119.02 – 119.03 Mb Chr 9: 44.31 – 44.31 Mb PubMed search
Wikidata
View/Edit Human View/Edit Mouse

Glucose-6-phosphate exchanger SLC37A4, also known as glucose-6-phosphate translocase, is an enzyme that in humans is encoded by the SLC37A4 gene.

It consists of three subunits, each of which are vital components of the multi-enzyme Glucose-6-Phosphatase Complex (G6Pase). This important enzyme complex is located within the membrane of the endoplasmic reticulum, and catalyzes the terminal reactions in both glycogenolysis and gluconeogenesis. The G6Pase complex is most abundant in liver tissue, but also present in kidney cells, small intestine, pancreatic islets and at a lower concentration in the gallbladder. The G6Pase complex is highly involved in the regulation of homeostasis and blood glucose levels. Within this framework of glucose regulation, the translocase components are responsible for transporting the substrates and products across the endoplasmic reticulum membrane, resulting in the release of free glucose into the bloodstream.

Structure

Glucose-6-phosphate translocase is a transmembrane protein providing a selective channel between the endoplasmic reticulum lumen and the cytosol. The enzyme is made up of three separate transporting subunits referred to as G6PT1 (subunit 1), G6PT2 (subunit 2) and G6PT3 (subunit 3). While the hydrolyzing component of the G6Pase complex is located on the side of the membrane on which it acts, namely facing the lumen, the translocases are all integral membrane proteins in order to perform their function as cross-membrane transporters. The translocases are spatially located on either side of the active site of the hydrolyzing component within the membrane, which allows the greatest speed and facility of the reaction.

Mechanism

Each of the translocase subunits performs a specific function in the transport of substrates and products, and finally release of glucose (which will eventually reach the bloodstream), as a step in glycogenolysis or gluconeogenesis. G6PT1 transports Glucose-6-Phosphate from the cytosol into the lumen of the endoplasmic reticulum, where it is hydrolyzed by the catalytic subunit of G6Pase. After hydrolysis, glucose and inorganic phosphate are transported back into the cytosol by G6PT2 and G6PT3, respectively. While the exact chemistry of the enzyme remains unknown, studies have shown that the mechanism of the enzyme complex is highly dependent upon the membrane structure. For instance, the Michaelis Constant of the enzyme for glucose-6-phosphate decreases significantly upon membrane disruption. The originally proposed mechanism of the G6Pase system involved a relatively unspecific hydrolase, suggesting that G6PT1 alone provides the high specificity for the overall reaction by selective transport into the lumen, where hydrolysis occurs. Supporting evidence for this proposed reaction includes the marked decrease in substrate specificity of hydrolysis upon membrane degradation.

Figure 1: Schematic representation of Glucose-6-Phosphate Translocase within the Glucose-6-Phosphatase Complex

Figure 1 illustrates the role of G6P-Translocase within the G6Pase complex.

Inhibitors

Many inhibitors of glucose-6-phosphate translocase of novel, semi-synthetic or natural origin are known and of medical importance. Genetic algorithms for synthesizing novel inhibitors of G6PT1 have been developed and utilized in drug discovery. Inhibitors of G6PT1 are the most studied as this subunit catalyzes the rate limiting step in glucose production through gluconeogenesis or glycogenolysis, and without its function these two processes could not occur. This inhibition holds great potential in drug development (discussed in "Medical and Disease Relevance"). Small-molecule inhibitors, such as mercaptopicolinic acid and diazobenzene sulfonate have some degree of inhibiting potential for G6PT1 but systematically lack specificity in inhibition, rendering them poor drug candidates. Since the late 1990s, natural products have been increasingly studied as potent and specific inhibitors of G6PT1. Prominent examples of natural inhibitors include mumbaistatin and analogs, kodaistatin (harvested from extracts of Aspergillus terreus) and chlorogenic acid. Other natural product inhibitors of G6PT1 are found in the fungi Chaetomium carinthiacum, Bauhinia magalandra leaves, and streptomyces bacteria.

Medical and disease relevance

1) Excessive activity of G6PT1 may contribute to the development of diabetes. Diabetes mellitus type 2 is a disease characterized by chronically elevated blood glucose levels, even when fasting. The rapidly rising prevalence of type 2 diabetes, along with its strong correlation to heart disease and other health complications has rendered it an area of intense research with an urgent need for treatment options. Studies monitoring blood glucose levels in rabbits revealed that the activity of G6Pase, and therefore G6PT1, is increased in specimens with diabetes. This strong correlation with diabetes type 2 makes the G6Pase complex, and G6PT1 in particular, an appealing drug target for control of blood glucose levels as its inhibition would directly prevent the release of free glucose into the bloodstream. It is possible that this mechanism of inhibition could be developed into a treatment for diabetes.

2) The absence of a functional G6PT1 enzyme causes glycogen storage disease type Ib, commonly referred to as von Gierke disease, in humans. A common symptom of this disease is a build-up of glycogen in the liver and kidney causing enlargement of the organs.

3) G6PT1 activity contributes to the survival of cells during hypoxia, which enables tumor cell growth and proliferation.

See also

• Solute carrier family

Further reading

• Chou JY, Matern D, Mansfield BC, Chen YT (March 2002). "Type I glycogen storage diseases: disorders of the glucose-6-phosphatase complex". Current Molecular Medicine. 2 (2): 121–143. doi:10.2174/1566524024605798. PMID 11949931.
• Narisawa K, Igarashi Y, Otomo H, Tada K (August 1978). "A new variant of glycogen storage disease type I probably due to a defect in the glucose-6-phosphate transport system". Biochemical and Biophysical Research Communications. 83 (4): 1360–1364. doi:10.1016/0006-291X(78)91371-2. PMID 212064.
• Fenske CD, Jeffery S, Weber JL, Houlston RS, Leonard JV, Lee PJ (April 1998). "Localisation of the gene for glycogen storage disease type 1c by homozygosity mapping to 11q". Journal of Medical Genetics. 35 (4): 269–272. doi:10.1136/jmg.35.4.269. PMC 1051271. PMID 9598717.
• Kure S, Suzuki Y, Matsubara Y, Sakamoto O, Shintaku H, Isshiki G, et al. (July 1998). "Molecular analysis of glycogen storage disease type Ib: identification of a prevalent mutation among Japanese patients and assignment of a putative glucose-6-phosphate translocase gene to chromosome 11". Biochemical and Biophysical Research Communications. 248 (2): 426–431. doi:10.1006/bbrc.1998.8985. PMID 9675154.
• Veiga-da-Cunha M, Gerin I, Chen YT, de Barsy T, de Lonlay P, Dionisi-Vici C, et al. (October 1998). "A gene on chromosome 11q23 coding for a putative glucose- 6-phosphate translocase is mutated in glycogen-storage disease types Ib and Ic". American Journal of Human Genetics. 63 (4): 976–983. doi:10.1086/302068. PMC 1377500. PMID 9758626.
• Marcolongo P, Barone V, Priori G, Pirola B, Giglio S, Biasucci G, et al. (October 1998). "Structure and mutation analysis of the glycogen storage disease type 1b gene". FEBS Letters. 436 (2): 247–250. Bibcode:1998FEBSL.436..247M. doi:10.1016/S0014-5793(98)01129-6. PMID 9781688. S2CID 21464560.
• Lin B, Annabi B, Hiraiwa H, Pan CJ, Chou JY (November 1998). "Cloning and characterization of cDNAs encoding a candidate glycogen storage disease type 1b protein in rodents". The Journal of Biological Chemistry. 273 (48): 31656–31660. doi:10.1074/jbc.273.48.31656. PMID 9822626.
• Ihara K, Kuromaru R, Hara T (October 1998). "Genomic structure of the human glucose 6-phosphate translocase gene and novel mutations in the gene of a Japanese patient with glycogen storage disease type Ib". Human Genetics. 103 (4): 493–496. doi:10.1007/s004390050856. PMID 9856496. S2CID 26410800.
• Ihara K, Takabayashi A, Terasaki K, Hara T (1999). "Assignment1 of glucose 6-phosphate translocase (G6PT1) to human chromosome band 11q23.3 by in situ hybridization". Cytogenetics and Cell Genetics. 83 (1–2): 50–51. doi:10.1159/000015167. PMID 9925924. S2CID 35304470.
• Gerin I, Veiga-da-Cunha M, Noël G, Van Schaftingen E (February 1999). "Structure of the gene mutated in glycogen storage disease type Ib". Gene. 227 (2): 189–195. doi:10.1016/S0378-1119(98)00614-3. PMID 10023055.
• Hiraiwa H, Pan CJ, Lin B, Moses SW, Chou JY (February 1999). "Inactivation of the glucose 6-phosphate transporter causes glycogen storage disease type 1b". The Journal of Biological Chemistry. 274 (9): 5532–5536. doi:10.1074/jbc.274.9.5532. PMID 10026167.
• Pan CJ, Lin B, Chou JY (May 1999). "Transmembrane topology of human glucose 6-phosphate transporter". The Journal of Biological Chemistry. 274 (20): 13865–13869. doi:10.1074/jbc.274.20.13865. PMID 10318794.
• Janecke AR, Bosshard NU, Mayatepek E, Schulze A, Gitzelmann R, Burchell A, et al. (March 1999). "Molecular diagnosis of type 1c glycogen storage disease". Human Genetics. 104 (3): 275–277. doi:10.1007/s004390050948. PMID 10323254. S2CID 42696446.
• Hou DC, Kure S, Suzuki Y, Hasegawa Y, Hara Y, Inoue T, et al. (September 1999). "Glycogen storage disease type Ib: structural and mutational analysis of the microsomal glucose-6-phosphate transporter gene". American Journal of Medical Genetics. 86 (3): 253–257. doi:10.1002/(SICI)1096-8628(19990917)86:3<253::AID-AJMG11>3.0.CO;2-7. PMID 10482875.
• Veiga-da-Cunha M, Gerin I, Chen YT, Lee PJ, Leonard JV, Maire I, et al. (September 1999). "The putative glucose 6-phosphate translocase gene is mutated in essentially all cases of glycogen storage disease type I non-a". European Journal of Human Genetics. 7 (6): 717–723. doi:10.1038/sj.ejhg.5200366. PMID 10482962.
• Galli L, Orrico A, Marcolongo P, Fulceri R, Burchell A, Melis D, et al. (October 1999). "Mutations in the glucose-6-phosphate transporter (G6PT) gene in patients with glycogen storage diseases type 1b and 1c". FEBS Letters. 459 (2): 255–258. Bibcode:1999FEBSL.459..255G. doi:10.1016/S0014-5793(99)01248-X. PMID 10518030. S2CID 41229244.
• Lam CW, Chan KY, Tong SF, Chan BY, Chan YT, Chan YW (July 2000). "A novel missense mutation (P191L) in the glucose-6-phosphate translocase gene identified in a Chinese family with glycogen storage disease 1b". Human Mutation. 16 (1): 94. doi:10.1002/1098-1004(200007)16:1<94::AID-HUMU26>3.0.CO;2-Q. PMID 10874322. S2CID 20061331.
• Santer R, Rischewski J, Block G, Kinner M, Wendel U, Schaub J, Schneppenheim R (August 2000). "Molecular analysis in glycogen storage disease 1 non-A: DHPLC detection of the highly prevalent exon 8 mutations of the G6PT1 gene in German patients". Human Mutation. 16 (2): 177. doi:10.1002/1098-1004(200008)16:2<177::AID-HUMU13>3.0.CO;2-8. PMID 10923042.