Sulfate-compatible density marks an intratrimeric junction in the Escherichia coli dihydrolipoamide succinyltransferase catalytic domain.

The catalytic domain of Escherichia coli dihydrolipoamide succinyltransferase (EcDSCD), the E2 component of the 2-oxoglutarate dehydrogenase complex, forms the oligomeric core of the multi-enzyme assembly. Here, we report the crystal structure of EcDSCD determined in space group F432. The F432 crystal symmetry captures a compact trimeric building block and a symmetry-expanded 24-subunit assembly consistent with the octahedral architecture of the E2 catalytic core. Structural analysis revealed sulfate-compatible electron density near Lys196 at a crystallographic threefold intratrimeric junction. Comparison with previously reported EcDSCD structures suggests that this density marks a structurally relevant oxyanion-sensitive hotspot at the intratrimeric junction. Notably, the α1-helix is positioned adjacent to the Lys196-centered junction and extends towards the active-site pocket, where it adopts a shifted orientation relative to other EcDSCD crystal forms. These observations link sulfate-compatible density, the intratrimeric junction and α1-helix positioning within the EcDSCD 24-mer, providing a structural framework for understanding local oxyanion-sensitive features in the E2 catalytic core.