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The N-terminal 1-55 residues domain of pyruvate dehydrogenase from Escherichia coli assembles as a dimer in solution.

The pyruvate dehydrogenase complex (PDHc) from Escherichia coli is a large protein complex consisting of multiple copies of the pyruvate dehydrogenase (E1ec), dihydrolipoamide acetyltransferase (E2ec) and dihydrolipoamide dehydrogenase (E3ec). The N-terminal domain (NTD, residues 1-55) of E1ec plays a critical role in the interaction between E1ec and E2ec and the whole PDHc activity. Using circular dichroism, size-exclusion chromatography and dynamic light scattering spectroscopy, we show that the NTD of E1ec presents dimeric assembly under physiological condition. Pull-down and isothermal titration calorimetry binding assays revealed that the E2ec peripheral subunit-binding domain (PSBD) forms a very stable complex with the NTD, indicating the isolated NTD functionally interacts with PSBD and the truncated E1ec (E1ec∆NTD) does not interact with PSBD. These findings are important to understand the mechanism of PDHc and other thiamine-based multi-component enzymes.