GOT2 is a dimer containing two identical subunits that hold overlapping subunit regions. The top and sides of the enzyme are made up of helices, while the bottom is formed by strands of beta sheets and extended hairpin loops. The subunit itself can be categorized into four different parts: a large domain, which binds pyridoxal-P, a small domain, an NH2-terminal arm, and a bridge across two domains, which is formed by residues 48-75 and 301-358.[2] Virtually ubiquitous in eukaryotic cells, GOT2 nucleic acid and protein sequences are highly conserved, and its 5’regulatory regions in genomic DNA resemble those of typical house-keeping genes in that, e.g.,they lack a TATA box.[3] The GOT2 gene is also located on 16q21 and has an exon count of 10.[1]
Function
In order to produce the energy needed for everyday activities, our body needs to go through the process of glycolysis, which breaks down glucose into pyruvate. In this pathway, one very important part is the reduction of NAD+ to NADH and then the rapid oxidation of NADH back into NAD+. The oxidation phase mainly occurs in the mitochondria as part of the electron transport chain, but the transfer of NADH into the mitochondria from the cytosol is impossible, due to the impermeability of the inner mitochondrial membrane to NADH. Therefore, the malate-aspartate shuttle is needed to transfer reducing equivalents across the mitochondrial membrane for energy production. GOT2 and another enzyme, MDH, are essential for the functioning of the shuttle. GOT2 converts oxaloacetate into aspartate by transamination. This aspartate as well as alpha-ketoglutarate return into the cytosol, which is then converted back to oxaloacetate and glutamate, respectively.[4]
Another function of GOT2 is that it is believed to transaminate kynurenine into kynurenic acid (KYNA) in the brain. The KYNA made by the GOT2 is thought to be an important factor in brain pathology. It is suggested that KYNA synthesized by GOT2 could constitute a common, and mechanistically relevant, feature of the neurotoxicity caused by mitochondrial poisons, such as otenone, malonate, 1-methyl-4-phenylpyridinium, and 3-nitropropionic acid.[5]
Clinical Significance
In nearly all cancer cells, glycolysis has been seen to be highly elevated to meet their increased energy, biosynthesis, and redox needs. Therefore, the malate-aspartate shuttle promotes the net transfer of cytosolic NADH into mitochondria to ensure a high rate of glycolysis in diverse cancer cell lines. In a study completed in 2008, inhibiting the malate-aspartate shuttle was found to impair the glycolysis process and essentially decreased breast adenocarcinoma cell proliferation. Furthermore, knocking down GOT2 and GOT1 has also been reported to inhibit cell proliferation and colony formation in pancreatic cancer cell lines, suggesting that the GOT enzyme is essential for maintaining a high rate of glycolysis to support rapid tumor cell growth. Also, both glucose and glutamine increase GOT2 3K acetylation in PANC-1 cells and that GOT2 3K acetylation plays a critical role in coordinating glucose and glutamine uptake to provide energy and support cell proliferation and tumor growth. This implies that inhibiting GOT2 3K acetylation may merit exploration as a therapeutic agent especially for pancreatic cancer.[4]
↑Zhou SL, Gordon RE, Bradbury M, Stump D, Kiang CL, Berk PD (Apr 1998). "Ethanol up-regulates fatty acid uptake and plasma membrane expression and export of mitochondrial aspartate aminotransferase in HepG2 cells". Hepatology. 27 (4): 1064–74. doi:10.1002/hep.510270423. PMID9537447.
↑Guidetti P, Amori L, Sapko MT, Okuno E, Schwarcz R (Jul 2007). "Mitochondrial aspartate aminotransferase: a third kynurenate-producing enzyme in the mammalian brain". Journal of Neurochemistry. 102 (1): 103–11. doi:10.1111/j.1471-4159.2007.04556.x. PMID17442055.
Further reading
Doonan S, Barra D, Bossa F (1985). "Structural and genetic relationships between cytosolic and mitochondrial isoenzymes". The International Journal of Biochemistry. 16 (12): 1193–9. doi:10.1016/0020-711X(84)90216-7. PMID6397370.
Furuya E, Yoshida Y, Tagawa K (May 1979). "Interaction of mitochondrial aspartate aminotransferase with negatively charged lecithin liposomes". Journal of Biochemistry. 85 (5): 1157–63. PMID376500.
Craig IW, Tolley E, Bobrow M, van Heyningen V (1979). "Assignment of a gene necessary for the expression of mitochondrial glutamic-oxaloacetic transaminase in human-mouse hybrid cells". Cytogenetics and Cell Genetics. 22 (1–6): 190–4. doi:10.1159/000130933. PMID752471.
Pol S, Bousquet-Lemercier B, Pavé-Preux M, Bulle F, Passage E, Hanoune J, Mattei MG, Barouki R (Sep 1989). "Chromosomal localization of human aspartate aminotransferase genes by in situ hybridization". Human Genetics. 83 (2): 159–64. doi:10.1007/BF00286710. PMID2777255.
Fahien LA, Kmiotek EH, MacDonald MJ, Fibich B, Mandic M (Aug 1988). "Regulation of malate dehydrogenase activity by glutamate, citrate, alpha-ketoglutarate, and multienzyme interaction". The Journal of Biological Chemistry. 263 (22): 10687–97. PMID2899080.
Pol S, Bousquet-Lemercier B, Pave-Preux M, Pawlak A, Nalpas B, Berthelot P, Hanoune J, Barouki R (Dec 1988). "Nucleotide sequence and tissue distribution of the human mitochondrial aspartate aminotransferase mRNA". Biochemical and Biophysical Research Communications. 157 (3): 1309–15. doi:10.1016/S0006-291X(88)81017-9. PMID3207426.
Fahien LA, Kmiotek EH, Woldegiorgis G, Evenson M, Shrago E, Marshall M (May 1985). "Regulation of aminotransferase-glutamate dehydrogenase interactions by carbamyl phosphate synthase-I, Mg2+ plus leucine versus citrate and malate". The Journal of Biological Chemistry. 260 (10): 6069–79. PMID3997814.
Martini F, Angelaccio S, Barra D, Pascarella S, Maras B, Doonan S, Bossa F (Nov 1985). "The primary structure of mitochondrial aspartate aminotransferase from human heart". Biochimica et Biophysica Acta. 832 (1): 46–51. doi:10.1016/0167-4838(85)90172-4. PMID4052435.
Davidson RG, Cortner JA, Rattazzi MC, Ruddle FH, Lubs HA (Jul 1970). "Genetic polymorphisms of human mitochondrial glutamic oxaloacetic transaminase". Science. 169 (3943): 391–2. doi:10.1126/science.169.3943.391. PMID5450376.
Jeremiah SJ, Povey S, Burley MW, Kielty C, Lee M, Spowart G, Corney G, Cook PJ (May 1982). "Mapping studies on human mitochondrial glutamate oxaloacetate transaminase". Annals of Human Genetics. 46 (Pt 2): 145–52. doi:10.1111/j.1469-1809.1982.tb00705.x. PMID7114792.
Tolley E, van Heyningen V, Brown R, Bobrow M, Craig IW (Oct 1980). "Assignment to chromosome 16 of a gene necessary for the expression of human mitochondrial glutamate oxaloacetate transaminase (aspartate aminotransferase) (E.C. 2.6.1.1.)". Biochemical Genetics. 18 (9–10): 947–54. doi:10.1007/BF00500127. PMID7225087.
Lain B, Iriarte A, Mattingly JR, Moreno JI, Martinez-Carrion M (Oct 1995). "Structural features of the precursor to mitochondrial aspartate aminotransferase responsible for binding to hsp70". The Journal of Biological Chemistry. 270 (42): 24732–9. doi:10.1074/jbc.270.42.24732. PMID7559589.
Maruyama K, Sugano S (Jan 1994). "Oligo-capping: a simple method to replace the cap structure of eukaryotic mRNAs with oligoribonucleotides". Gene. 138 (1–2): 171–4. doi:10.1016/0378-1119(94)90802-8. PMID8125298.
Suzuki Y, Yoshitomo-Nakagawa K, Maruyama K, Suyama A, Sugano S (Oct 1997). "Construction and characterization of a full length-enriched and a 5'-end-enriched cDNA library". Gene. 200 (1–2): 149–56. doi:10.1016/S0378-1119(97)00411-3. PMID9373149.
