Detecting single photons: A supramolecular matter?

Rod photoreceptors detect single photons through a tradeoff of light collecting ability, amplification and speed. Key roles are played by rhodopsin (Rh) and transducin (Gt), whose complex supramolecular organization in outer segment disks begs for a functional interpretation. Here we review past and recent evidence of a temperature-dependence of photon detection by mammalian rods, and link this phenomenon with the putative oligomeric organization of Rh and new ideas on the dynamics of Rh–Gt interaction. Identifying an electrophysiological correlate of the supramolecular organization of Rh and Gt may shed light on the evolutionary advantage it confers to night vision.

► Rhodopsin has been reported to natively dimerize and oligomerize in rod disks.
► This poses conceptual challenges to the classical model of phototransduction.
► We present neglected data on the effect of temperature on single photon signaling.
► This data may link rod function to the supramolecular organization of rhodopsin.