| OGDH, also termed 2‑oxoglutarate dehydrogenase E1 component, is the thiamine‑dependent decarboxylase subunit of the mitochondrial 2‑oxoglutarate dehydrogenase complex (OGDHC) and catalyzes the first, rate‑limiting step in the overall conversion of 2‑oxoglutarate to succinyl‑CoA and CO₂ in the tricarboxylic acid (TCA) cycle, linking catabolism of carbohydrates, fatty acids, and amino acids to NADH production for oxidative phosphorylation. The enzyme resides predominantly in the mitochondrial matrix and recognizes 2‑oxoglutarate via a ThDP cofactor at its active site, where it performs irreversible oxidative decarboxylation to form a covalent acyl‑ThDP intermediate, transfers this acyl group to the lipoamide arm of the E2 component DLST, and thereby initiates a multi‑step acyl‑transfer and reoxidation sequence that is completed by the E3 dihydrolipoamide dehydrogenase subunit; this sequence results in succinyl‑CoA formation and multiple reducing equivalents that feed the respiratory chain. OGDH activity lies far from thermodynamic equilibrium and operates as a key control point for TCA cycle flux and overall cellular respiration, with its catalytic rate and substrate preference tuning entry of glutamine‑derived carbon into the cycle and influencing the balance between energy production and biosynthetic precursor supply. The OGDHC can also accept 2‑oxoadipate as a low‑efficiency substrate, indicating some flexibility at the level of dicarboxylic acid processing while maintaining a strong preference for 2‑oxoglutarate as the primary metabolic node. Beyond its classical metabolic role, a fraction of the complex localizes to chromatin, where OGDH associates with the histone acetyltransferase KAT2A and provides locally generated succinyl‑CoA for histone lysine succinylation, connecting mitochondrial TCA chemistry directly to nuclear acyl‑modification of histones and transcriptional regulation. Functional perturbation of OGDH in human embryonic stem cells demonstrates that OGDH‑dependent TCA cycle activity is necessary to sustain mitochondrial respiration, maintain ATP levels comparable to glycolytic output, and preserve a transcriptional program compatible with primed pluripotent identity, as loss of OGDH disrupts TCA intermediates, diminishes oxidative phosphorylation, lowers total ATP, and leads to cell death and broad transcriptional dysregulation. In cancer, OGDH supports glutamine‑fueled anaplerosis, aspartate production, and mitochondrial bioenergetics, and contributes to oncogenic signaling by enhancing Wnt/β‑catenin pathway activation and promoting proliferation and invasion in gastric cancer, while altered OGDH activity and its downstream signaling effects are being explored as metabolic vulnerabilities for targeted therapy. |
