IDH3G explained

Isocitrate dehydrogenase [NAD] subunit gamma, mitochondrial is an enzyme that in humans is encoded by the IDH3G gene.^{[1] [2]}

Isocitrate dehydrogenases (IDHs) catalyze the oxidative decarboxylation of isocitrate to 2-oxoglutarate. These enzymes belong to two distinct subclasses, one of which utilizes NAD(+) as the electron acceptor and the other NADP(+). Five isocitrate dehydrogenases have been reported: three NAD(+)-dependent isocitrate dehydrogenases, which localize to the mitochondrial matrix, and two NADP(+)-dependent isocitrate dehydrogenases, one of which is mitochondrial and the other predominantly cytosolic. NAD(+)-dependent isocitrate dehydrogenases catalyze the allosterically regulated rate-limiting step of the tricarboxylic acid cycle. Each isozyme is a heterotetramer that is composed of two alpha subunits, one beta subunit, and one gamma subunit. The protein encoded by this gene is the gamma subunit of one isozyme of NAD(+)-dependent isocitrate dehydrogenase. This gene is a candidate gene for periventricular heterotopia. Several alternatively spliced transcript variants of this gene have been described, but only some of their full length natures have been determined. [provided by RefSeq, Jul 2008]

Structure

IDH3 is one of three isocitrate dehydrogenase isozymes, the other two being IDH1 and IDH2, and encoded by one of five isocitrate dehydrogenase genes, which are IDH1, IDH2, IDH3A, IDH3B, and IDH3G.^[3] The genes IDH3A, IDH3B, and IDH3G encode subunits of IDH3, which is a heterotetramer composed of two 37-kDa α subunits (IDH3α), one 39-kDa β subunit (IDH3β), and one 39-kDa γ subunit (IDH3γ), each with distinct isoelectric points.^{[4] [5] [6]} Alignment of their amino acid sequences reveals ~40% identity between IDH3α and IDH3β, ~42% identity between IDH3α and IDH3γ, and an even closer identity of 53% between IDH3β and IDH3γ, for an overall 34% identity and 23% similarity across all three subunit types.^{[5] [6] [7] [8]} Notably, Arg88 in IDH3α is essential for IDH3 catalytic activity, whereas the equivalent Arg99 in IDH3β and Arg97 in IDH3γ are largely involved in the enzyme's allosteric regulation by ADP and NAD.^[7] Thus, it is possible that these subunits arose from gene duplication of a common ancestral gene, and the original catalytic Arg residue were adapted to allosteric functions in the β- and γ-subunits.^{[5] [7]} Likewise, Asp181 in IDH3α is essential for catalysis, while the equivalent Asp192 in IDH3β and Asp190 in IDH3γ enhance NAD- and Mn²⁺-binding.^[5] Since the oxidative decarboxylation catalyzed by IDH3 requires binding of NAD, Mn²⁺, and the substrate isocitrate, all three subunits participate in the catalytic reaction.^{[6] [7]} Moreover, studies of the enzyme in pig heart reveal that the αβ and αγ dimers constitute two binding sites for each of its ligands, including isocitrate, Mn²⁺, and NAD, in one IDH3 tetramer.^{[5] [6]}

Function

As an isocitrate dehydrogenase, IDH3 catalyzes the irreversible oxidative decarboxylation of isocitrate to yield α-ketoglutarate (α-KG) and CO₂ as part of the TCA cycle in glucose metabolism.^{[4] [5] [6] [7] [9]} This step also allows for the concomitant reduction of NAD+ to NADH, which is then used to generate ATP through the electron transport chain. Notably, IDH3 relies on NAD+ as its electron acceptor, as opposed to NADP+ like IDH1 and IDH2.^{[4] [5]} IDH3 activity is regulated by the energy needs of the cell: when the cell requires energy, IDH3 is activated by ADP; and when energy is no longer required, IDH3 is inhibited by ATP and NADH.^{[5] [6]} This allosteric regulation allows IDH3 to function as a rate-limiting step in the TCA cycle.^{[9] [10]} Within cells, IDH3 and its subunits have been observed to localize to the mitochondria.^{[5] [6] [9]}

Clinical Significance

The IDH3G gene may be involved in drug resistance in gastric cancer.^[11]

See also

• IDH1
• IDH2
• IDH3A
• IDH3B

Further reading

• Sandoval N, Bauer D, Brenner V, etal . The genomic organization of a human creatine transporter (CRTR) gene located in Xq28. . Genomics . 35 . 2 . 383–5 . 1996 . 8661155 . 10.1006/geno.1996.0373 .
• Kim YO, Koh HJ, Kim SH, etal . Identification and functional characterization of a novel, tissue-specific NAD(+)-dependent isocitrate dehydrogenase beta subunit isoform. . J. Biol. Chem. . 274 . 52 . 36866–75 . 2000 . 10601238 . 10.1074/jbc.274.52.36866 . free .
• Weiss C, Zeng Y, Huang J, etal . Bovine NAD+-dependent isocitrate dehydrogenase: alternative splicing and tissue-dependent expression of subunit 1. . Biochemistry . 39 . 7 . 1807–16 . 2000 . 10677231 . 10.1021/bi991691i .
• Hartley JL, Temple GF, Brasch MA . DNA cloning using in vitro site-specific recombination. . Genome Res. . 10 . 11 . 1788–95 . 2001 . 11076863 . 10.1101/gr.143000 . 310948 .
• Simpson JC, Wellenreuther R, Poustka A, etal . Systematic subcellular localization of novel proteins identified by large-scale cDNA sequencing. . EMBO Rep. . 1 . 3 . 287–92 . 2001 . 11256614 . 10.1093/embo-reports/kvd058 . 1083732 .
• Strausberg RL, Feingold EA, Grouse LH, etal . Generation and initial analysis of more than 15,000 full-length human and mouse cDNA sequences. . Proc. Natl. Acad. Sci. U.S.A. . 99 . 26 . 16899–903 . 2003 . 12477932 . 10.1073/pnas.242603899 . 139241 . 2002PNAS...9916899M . free .
• Gerhard DS, Wagner L, Feingold EA, etal . The status, quality, and expansion of the NIH full-length cDNA project: the Mammalian Gene Collection (MGC). . Genome Res. . 14 . 10B . 2121–7 . 2004 . 15489334 . 10.1101/gr.2596504 . 528928 .
• Wiemann S, Arlt D, Huber W, etal . From ORFeome to biology: a functional genomics pipeline. . Genome Res. . 14 . 10B . 2136–44 . 2004 . 15489336 . 10.1101/gr.2576704 . 528930 .
• Rual JF, Venkatesan K, Hao T, etal . Towards a proteome-scale map of the human protein-protein interaction network. . Nature . 437 . 7062 . 1173–8 . 2005 . 16189514 . 10.1038/nature04209 . 2005Natur.437.1173R . 4427026 .
• Mehrle A, Rosenfelder H, Schupp I, etal . The LIFEdb database in 2006. . Nucleic Acids Res. . 34 . Database issue . D415–8 . 2006 . 16381901 . 10.1093/nar/gkj139 . 1347501 .
• Soundar S, O'hagan M, Fomulu KS, Colman RF . Identification of Mn2+-binding aspartates from alpha, beta, and gamma subunits of human NAD-dependent isocitrate dehydrogenase. . J. Biol. Chem. . 281 . 30 . 21073–81 . 2006 . 16737955 . 10.1074/jbc.M602956200 . free .
• Bzymek KP, Colman RF . Role of alpha-Asp181, beta-Asp192, and gamma-Asp190 in the distinctive subunits of human NAD-specific isocitrate dehydrogenase. . Biochemistry . 46 . 18 . 5391–7 . 2007 . 17432878 . 10.1021/bi700061t .

Notes and References

1. Brenner V, Nyakatura G, Rosenthal A, Platzer M . Genomic organization of two novel genes on human Xq28: compact head to head arrangement of IDH gamma and TRAP delta is conserved in rat and mouse . Genomics . 44 . 1 . 8–14 . November 1997 . 9286695 . 10.1006/geno.1997.4822 .
2. Web site: Entrez Gene: IDH3G isocitrate dehydrogenase 3 (NAD+) gamma.
3. Dimitrov L, Hong CS, Yang C, Zhuang Z, Heiss JD . New developments in the pathogenesis and therapeutic targeting of the IDH1 mutation in glioma . International Journal of Medical Sciences . 12 . 3 . 201–13 . 2015 . 25678837 . 10.7150/ijms.11047 . 4323358.
4. Zeng. L. Morinibu. A. Kobayashi. M. Zhu. Y. Wang. X. Goto. Y. Yeom. CJ. Zhao. T. Hirota. K. Shinomiya. K. Itasaka. S. Yoshimura. M. Guo. G. Hammond. EM. Hiraoka. M. Harada. H. Aberrant IDH3α expression promotes malignant tumor growth by inducing HIF-1-mediated metabolic reprogramming and angiogenesis.. Oncogene. 3 September 2015. 34. 36. 4758–66. 25531325. 10.1038/onc.2014.411. free.
5. Bzymek. KP. Colman. RF. Role of alpha-Asp181, beta-Asp192, and gamma-Asp190 in the distinctive subunits of human NAD-specific isocitrate dehydrogenase.. Biochemistry. 8 May 2007. 46. 18. 5391–7. 17432878. 10.1021/bi700061t.
6. Soundar. S. O'hagan. M. Fomulu. KS. Colman. RF. Identification of Mn2+-binding aspartates from alpha, beta, and gamma subunits of human NAD-dependent isocitrate dehydrogenase.. The Journal of Biological Chemistry. 28 July 2006. 281. 30. 21073–81. 16737955. 10.1074/jbc.m602956200. free.
7. Soundar. S. Park. JH. Huh. TL. Colman. RF. Evaluation by mutagenesis of the importance of 3 arginines in alpha, beta, and gamma subunits of human NAD-dependent isocitrate dehydrogenase.. The Journal of Biological Chemistry. 26 December 2003. 278. 52. 52146–53. 14555658. 10.1074/jbc.m306178200. free.
8. Dange. M. Colman. RF. Each conserved active site tyr in the three subunits of human isocitrate dehydrogenase has a different function.. The Journal of Biological Chemistry. 2 July 2010. 285. 27. 20520–5. 20435888. 10.1074/jbc.m110.115386. 2898308. free.
9. Huh TL, Kim YO, Oh IU, Song BJ, Inazawa J . Assignment of the human mitochondrial NAD+ -specific isocitrate dehydrogenase alpha subunit (IDH3A) gene to 15q25.1→q25.2by in situ hybridization . Genomics . 32 . 2 . 295–6 . May 1997 . 8833160 . 10.1006/geno.1996.0120 .
10. Yoshimi. N. Futamura. T. Bergen. SE. Iwayama. Y. Ishima. T. Sellgren. C. Ekman. CJ. Jakobsson. J. Pålsson. E. Kakumoto. K. Ohgi. Y. Yoshikawa. T. Landén. M. Hashimoto. K. Cerebrospinal fluid metabolomics identifies a key role of isocitrate dehydrogenase in bipolar disorder: evidence in support of mitochondrial dysfunction hypothesis.. Molecular Psychiatry. 19 January 2016. 21. 11. 1504–1510. 26782057. 10.1038/mp.2015.217. 5078854.
11. Zhou. J. Yong. WP. Yap. CS. Vijayaraghavan. A. Sinha. RA. Singh. BK. Xiu. S. Manesh. S. Ngo. A. Lim. A. Ang. C. Xie. C. Wong. FY. Lin. SJ. Wan. WK. Tan. IB. Flotow. H. Tan. P. Lim. KH. Yen. PM. Goh. LK. An integrative approach identified genes associated with drug response in gastric cancer.. Carcinogenesis. April 2015. 36. 4. 441–51. 25742747. 10.1093/carcin/bgv014. free.