Dissecting Bioelectrical Networks in Photosynthetic Membranes with Electrochemistry.

Photosynthetic membranes contain complex networks of redox proteins and molecules, which direct electrons along various energy-to-chemical interconversion reactions important for sustaining life on Earth. Analyzing and disentangling the mechanisms, regulation, and interdependencies of these electron transfer pathways is extremely difficult, owing to the large number of interacting components in the native membrane environment. While electrochemistry is well established for studying electron transfer in purified proteins, it has proved difficult to wire into proteins within their native membrane environments and even harder to probe on a systems-level the electron transfer networks they are entangled within. Here, we show how photosynthetic membranes from cyanobacteria can be wired to electrodes to access their complex electron transfer networks. Measurements of native membranes with structured electrodes revealed distinctive electrochemical signatures, enabling analysis from the scale of individual proteins to entire biochemical pathways as well as their interplay. This includes measurements of overlapping photosynthetic and respiratory pathways, the redox activities of membrane-bound quinones, along with validation using spectroscopic measurements. Importantly, we further demonstrated extraction of electrons from native membrane-bound Photosystem I at -600 mV versus SHE, which is ∼1 V more negative than from purified photosystems. This finding opens up opportunities for biotechnologies for solar electricity, fuel, and chemical generation. We foresee this electrochemical method being adapted to analyze other photosynthetic and nonphotosynthetic membranes, as well as aiding the development of new biocatalytic, biohybrid, and biomimetic systems.