Direct interaction between a membrane domain subunit and a connector subunit in the H+-translocating NADH-quinone oxidoreductase

When Paracoccus denitrificans membranes were treated with a crosslinker, m- maleimidobenzoyl-N-hydroxysuccinimide ester (MBS), a cross-linked product o f M-r similar to 31 kDa was found which reacted with antibodies against the hydrophobic subunit Nqo7 and the connector subunit Nqo6. NaI treatment of the Paracoccus membranes before, but not after, the crosslinking step preve nted the formation of the 31 kDa band. When Nqo7 and Nqo6 were coexpressed in Escherichia coli, both subunits were located in the membrane fraction. N IBS treatment of the E. coli membranes generated the 31 kDa band as in the Paracoccus membranes. These results indicate that Nqo7 interacts with proba ble N2-binding Nqo6. (C) 2001 Published by Elsevier Science B.V. on behalf of the Federation of European Biochemical Societies.