3.E.1.6.12
Blue-light absorbing proteorhodopsin (BPR) of 251 aas and 8 TMSs including a cleavable N-terminal TMS. BPR does not rely on the Sec pathway for inner membrane integration (Soto-Rodríguez and Baneyx 2018). The BPR signal sequence is recognized by the signal recognition particle (SRP; a protein that orchestrates the cotranslational biogenesis of inner membrane proteins) and serves as a beneficial "pro" domain rather than a traditional secretory peptide. It is a light-driven proton pump that may have a regulatory rather than energy harvesting function, based on light-induced opening of proton channels to modulate cell physiology depending on light intensity variations. It could therefore be a sensory rhodopsin, potentially associated with a transducer component. It presents a much slower photocycle than that of the green-absorbing proteorhodopsin, probably an adaptation to the intensity of solar illumination at a depth of 75m, where this bacterium was collected. Transport occurs only at pHs above 7 and is unidirectional.