What is it about?
Writing the direction of a light-driven protein pump with an electric field. Some microbial proteins, called proteorhodopsins, pump ions across cell membranes when illuminated. Whether the resulting current flows one way or the other depends on which way each protein is oriented in the membrane. Here we reconstitute TARA76, an unusually robust proteorhodopsin, into an artificial lipid bilayer inside a microfluidic device, and record its light-induced currents with picoampere sensitivity. Our main result is that the protein's orientation can be programmed: a writing field applied during membrane formation sets the direction of the photocurrent, which is then read out with a separate reading field during measurement. This gives deterministic control over the polarity of a bio-photonic transducer.
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Why is it important?
Protein-based photodetectors usually rely on whatever orientation the proteins happen to adopt when inserted into a membrane — a random, uncontrolled process that washes out any directional response. Our findings show that this orientation can instead be written in deliberately: applying a defined electric field while the bilayer forms produces a preferential alignment of TARA76, and therefore a photocurrent whose direction is set by the experimenter rather than by chance. This separates two roles that are normally conflated — a writing field that defines the polarity during assembly, and a reading field that probes it afterwards. The platform is fully acellular, works at room temperature, and needs no ionophores or protonophores, making it a practical route toward bioelectronic interfaces with defined polarity. This work is currently available as a preprint and has not yet been peer reviewed.
Perspectives
What I find most satisfying about this work is that the central result is not a number but a capability. Reconstituting a fragile membrane protein in a fully artificial system is already delicate work; getting it to sit in a defined orientation, on demand, is a different kind of problem altogether. It turned out that the two roles had to be separated cleanly: a writing field applied while the bilayer forms, which imprints a preferential orientation on the protein, and a reading field applied afterwards, which drives the photocurrent without altering that orientation. Once we made that distinction, the behaviour became reproducible and the direction of the photocurrent became something we could choose rather than something we measured. Along the way we noticed several secondary effects — an unexpected sensitivity to sodium ions, a light-induced modulation of the membrane's AC conductance, an equivalent-circuit picture that fits the whole response. These are interesting in their own right, but I think of them mainly as evidence that TARA76 is a well-behaved, vectorial transducer worth controlling in the first place. The robustness of this particular rhodopsin, which survives even complete dehydration, is what made the acellular platform practical. My hope is that this encourages a shift in how protein-based photodetectors are built: not by accepting whatever orientation self-assembly provides, but by writing the direction in from the start.
Dr Lorenzo Dominici
CNR NANOTEC, Institute of Nanotechnology
Read the Original
This page is a summary of: Electrically programmable picoscale phototransduction of a newly discovered microbial rhodopsin, May 2026, openRxiv,
DOI: 10.64898/2026.05.29.728716.
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