How does bacteriorhodopsin transport protons?

Bacteriorhodopsin is a light-driven proton pump, and it transports protons across the membrane by inducing conformational changes upon absorbing light. When light hits the retinal molecule within bacteriorhodopsin, it undergoes a series of structural changes. This process involves the transition of retinal from a cis to a trans configuration, which triggers a cascade of conformational changes in the surrounding protein structure. These changes facilitate the movement of protons from the inside of the cell to the outside across the membrane, effectively creating a proton gradient.

The generation of this gradient can then be utilized by the cell for ATP synthesis through ATP synthase, highlighting the role of bacteriorhodopsin in energy production in certain microorganisms. This mechanism is distinct from processes such as passive diffusion or the use of ion channels, which do not involve the energy of absorbed light to drive proton transport.