Cross‐linking study of membrane subunits K, L, M and N in E. coli complex I (997.10)

Abstract

Complex I is an entry point of the electron transport chain and plays a major role in proton gradient generation. Oxidation of NADH, reduction of ubiquinone, and proton translocation are three essential functions of Complex I. Subunits L, M, and N, the three largest subunits in the membrane domain, are homologous to components of multi‐subunit Na+/H+ antiporters, so they are implicated in proton pumping. Based on available evidence it is believed that a redox‐linked conformational change is necessary for proton pumping. According to recent crystal structures, subunit L contains an unusual helix HL extending laterally along the membrane surface from subunit L, past subunit M, and to subunits N and K. In this study, cross‐linking of engineered cysteine residues using disulfide formation and bi‐functional reagents was carried out to detect regions of the proton transporter that have restricted motion. Fourteen cysteine pairs between helix HL and membrane subunits L, M, N and K were cross‐linked and none showed no significant loss of enzyme activity or proton pumping These results suggest that there is not significant movement of the lateral helix. Further cross‐linking studies were done between pairs of cysteine residues within subunit N. The results of those studies suggested possible proton pathways.Grant Funding Source: NIH 1R15GM099014