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. 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. The GOT2 gene is also located on 16q21 and has an exon count of 10.
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.
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.
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