Authors: Gutierrez-Sanz, O; Forbig, E; Batista, AP; Pereira, MM; Salewski, J; Mroginski, MA; Gotz, R; De Lacey, AL; Kozuch, J; Zebger, I

Langmuir. vol: 34. page: 0743-7463.
Date: may-22. 2018.
Doi: 10.1021/acs.langmuir.7b04057.

Respiratory complex I (CpI) is a key player in the way organisms obtain energy, being an energy transducer, which couples nicotinamide adenine dinucleotide (NADH)/quinone oxidoreduction with proton translocation by a mechanism that remains elusive so far. In this work, we monitored the function of CpI in a biomimetic, supported lipid membrane system assembled on a 4-aminothiophenol (4-ATP) self-assembled monolayer by surface-enhanced infrared absorption spectroscopy. 4-ATP serves not only as a linker molecule to a nanostructured gold surface but also as pH sensor, as indicated by concomitant density functional theory calculations. In this way, we were able to monitor NADH/quinone oxidoreduction-induced transmembrane proton translocation via the protonation state of 4-ATP, depending on the net onentation of CpI molecules induced by two complementary approaches. An associated change of the amide I/amide II band intensity ratio indicates conformational modifications upon catalysis which may involve movements of transmembrane helices or other secondary structural elements, as suggested in the literature..