THE ROLE OF THE SURFACE GROUP IN FUNNELLING OF PROTONS TOWARDS THE PROTONIC CHANNEL OF BACTERIORHODOPSIN

The dynamics of proton transfer between the bulk and an indicator atta ched to a defined site on a protein (bacteriorhodopsin) was measured i n the time resolved domain. The labelling was attached to the cytoplas mic surface of the protein at the opening of its proton conducting cha nnel (residue 38). Detailed analysis of the results indicates that a n earby carboxylate (aspartate 36) functions as a relay group that accel erates the entrance of proton to the channel. A farther located cluste r, of 3 carboxylates, also functions in the same mode. These observati ons indicate that the surface of the protein had evolved as a function al element in directing the substrate towards the active site.