Mobile sequences in the pyruvate dehydrogenase complex, the E2 component, the catalytic domain and the 2-oxoglutarate dehydrogenase complex of Azotobacter vinelandii, as detected by 600 MHz 1H-NMR spectroscopy

600 MHz 1H-NMR spectroscopy demonstrates that the pyruvate dehydrogenase complex of Azotobacter vinelandii contains regions of the polypeptide chain with intramolecular mobility. This mobility is located in the E2 component and can probably be ascribed to alanine-proline-rich regions that link the lipoyl subdomains to each other as well as to the E1 and E3 binding domain. In the catalytic domain of E2, which is thought to form a compact, rigid core, also conformational flexibility is observed. It is conceivable that the N-terminal region of the catalytic domain, which contains many alanine residues, is responsible for the observed mobility. In the low-field region of the 1H-NMR spectrum of E2 specific resonances are found, which can be ascribed to mobile phenylalanine, histidine and/or tyrosine residues which are located in the E1 and E3 binding domain that links the lipoyl domain to the catalytic domain. In the 1H-NMR spectrum of the intact complex, these resonances cannot be observed, indicating a decreased mobility of the E1 and E3 binding domain.