Protein–Protein Interaction Regulates the Direction of Catalysis and Electron Transfer in a Redox Enzyme Complex

Abstract

Protein–protein interactions are well-known to regulate enzyme activity in cell signaling and metabolism. Here, we show that protein–protein interactions regulate the activity of a respiratory-chain enzyme, CymA, by changing the direction or bias of catalysis. CymA, a member of the widespread NapC/NirT superfamily, is a menaquinol-7 (MQ-7) dehydrogenase that donates electrons to several distinct terminal reductases in the versatile respiratory network of Shewanella oneidensis. We report the incorporation of CymA within solid-supported membranes that mimic the inner membrane architecture of S. oneidensis. Quartz-crystal microbalance with dissipation (QCM-D) resolved the formation of a stable complex between CymA and one of its native redox partners, flavocytochrome c3 (Fcc3) fumarate reductase. Cyclic voltammetry revealed that CymA alone could only reduce MQ-7, while the CymA-Fcc3 complex catalyzed the reaction required to support anaerobic respiration, the oxidation of MQ-7. We propose that MQ-7 oxidation in CymA is limited by electron transfer to the hemes and that complex formation with Fcc3 facilitates the electron-transfer rate along the heme redox chain. These results reveal a yet unexplored mechanism by which bacteria can regulate multibranched respiratory networks through protein–protein interactions.

A dynamic periplasmic electron transfer network enables respiratory flexibility beyond a thermodynamic regulatory regime

“…As these are interconnected, it seems likely that only the presence of a certain electron acceptor triggers the electron flow into one particular reaction. Still, the question of whether periplasmic electron transfer follows weak interactions or the formation of static protein complexes is still under debate, because McMillan et al (2013) observed CymA-triggered absorption of FccA onto lipid vesicles in an in vitro system. Thus far, what this experimental result infers for the in vivo situation remains unresolved.…”

Biohydrogen for a New Generation of H2/O2 Biofuel Cells: A Sustainable Energy Perspective

“…[143,164] Apart from a specific orientation for high electron-transfer rate, the channel for substrate diffusion must not be hindered upon immobilization of the enzyme on the electrode. [165] This aspect has not been investigated so far for Hases or MCOs. Furthermore, the reconstitution of a physiological chain at an electrochemical interface can be complicated by the competition between favorable orientation of one partner at the interface and favorable orientation for the other partner recognition.…”

H2‐Fueled ATP Synthesis on an Electrode: Mimicking Cellular Respiration

“…Great progress in immobilizing enzymes has allowed the exploitation of their substrate specificity to catalyze chemical reactions for industrial applications5 and to develop biosensors with great selectivity and capacity to detect analytes 6. However, to mimic and utilize the vectorial ion movement required for the generation of electrochemical gradients in living cells, both spatial control over the assembly of the participating proteins,7 and the presence and maintenance of two independent ion‐impermeable compartments are required 8. Liposomes,9 where a lipid bilayer separates the inner content from the outer solution, have been used as model systems to couple light energy to different biochemical reactions.…”