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Crystal structure — pig GTP-specific SCS (shown in 3D)
PDB 2FP4 — GTP-specific succinyl-CoA synthetase αβ dimer with GTP, K⁺ and Mg²⁺ bound, Fraser ME et al., J Biol Chem 2006, PMID:16481318. GTP sits in the ATP-grasp domain of the β subunit; the guanine base is recognized by Gln-20β and the γ-phosphate is clamped by Arg-54β.
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Mechanism — phospho-His & substrate-level phosphorylation
The α-subunit His (His-299 in the pig sequence) forms the classic phospho-histidine intermediate. Succinyl phosphate is the enzyme-bound intermediate: succinyl-CoA + Pi → succinyl-P, then succinyl-P + His → succinate + His-P, then His-P + GDP → GTP. Review: Fraser ME et al., JBC 2006 (above); classic mechanism in Lehninger Principles of Biochemistry, chapter on the citric acid cycle.
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Sequence
Human SUCLG1 (α) UniProt P53597 · SUCLG2 (β, GTP-specific) UniProt Q96I99 · NCBI Gene 8801 (SUCLG1)
› The 3D protein is the real GTP-specific SCS αβ dimer (PDB 2FP4) with its genuine GTP / K⁺ / Mg²⁺. Substrates, intermediates and GDP are drawn as compact schematic molecules at the active-site pocket and are labeled [schematic]. The catalytic His (α subunit) and the nucleotide-pocket residues come straight from the structure.