Protein-protein interaction converts a proton pump into a sensory receptor

摘要: John L. Spudich Department of Microbiology and Molecular Genetics University Texas Medical School Houston, 77030 As Max Delbriick noted 20 years ago, there is a remarkably small group chromophores used by biological photo- transducers that perform diverse functions (for general review see Lipson Horwitz, 1991). The two main classes photoactive proteins, energy-transducing pig- ments sensory receptors, use similar chromophoric prosthetic groups but carry out distinctly different actions following light absorption. Energy transducers, found most commonly in photosynthetic electron transfer assemblies, photons to drive formation energy-conserving pro- ton electrochemical potential across the membrane. Sen- sory on other hand, vision taxis systems microorganisms, photon absorption trigger activation signal via protein-pro- tein interaction. Recent work phototaxis receptor rhodopsin (SR)-I Halobacterium salinarium shows removal its tightly bound transducer protein uncovers light-driven proton transport activity. con- version SRI photoreactions from an energetic sen- function may provide insight into evolutionary relationship between these fundamental proteins. Retinylidene proteins (“rhodopsins”) form wide-spread family pigments. Their characteristic fea- tures are single polypeptide folds seven mem- brane-spanning a-helical segments, vitamin A aldehyde (retinal) as chromophore, attachment retinal internal pocket protonated Schiff base linkage lysine residue middle seventh helix. Prokaryotic rhodopsins types: ion pumps, such translocator bacteriorho- dopsin (BR) chloride pump halorhodopsin (HR), photosensory receptors SR-II recent reviewsseeoesterhelt Mar-wan, 1993; Spudich, 1993). Eukaryotic rhodop- sins visual pigments throughout animal world. In general, undergo site depro- tonation. BR (h,,,ax, 568 nm), best-characterized reti- nylidene terms structure/function, ab- sorption causes isomerization results deprotonation base, reaction central mechanism (Mathies et al., 1991; Oesterhelt 1992; Rothschild, Krebs Khorana, Lanyi, Photoisomerization-induced also essential for bo- vine (h,,,, 495 although not pumped membrane (Hofmann Heck, 1994). If blocked chromophore ana- logs or methylation nitrogen, signaling state, M-11~ (subscript denotes I.,,,), which acti-