Phoborhodopsin, a repellent phototaxis receptor in Halobacterium halobium, exhibits vibrational fine structure, a feature that has not been identified for any other rhodopsin pigment at physiological temperatures. This conclusion follows form analysis of the absorption properties of the pigment in H. halobium membranes containing native retinal and an array of retinal analogues. The absorption spectrum of the native pigment has a maximum at 487 nm with a pronounced shoulder at 460 nm; however, the bandwidth is that expected for a single retinylidene species. Gaussian band-shape simulation with a spacing corresponding to the vibrational frequencies of polyene stretching modes reproduces the structured absorption spectra of native pigment as well as of analogue phoborhodopsin. Absorption shifts produced by a series of dihydroretinal and other retinal analogues strongly indicate that the dominant factor regulating the color of the pigment is planarization of the retinal ring with respect to the polyene chain.

Color regulation in the archaebacterial phototaxis receptor phoborhodopsin (sensory rhodopsin II)

The protonated Schiff bases of all-trans-retinal and its double bond isomers, 11-cis- and 13-cis-retinals, comprise the chromophores of bacteriorhodopsin, sensory rhodopsin, rhodopsin, and the Chlamydomonas photoreceptor pigment. Absorption of photons by these chromophores is directly responsible for the functioning of the various photopigments. Clarification of their extremely complex structures and mechanisms requires multidisciplinary collaboration. The study of synthetic retinal analogs and pigments reconstituted from analogs provides a powerful and indispensable tool for such clarification. This article summarizes the application of retinal analogs in the bioorganic, biophysical, and biochemical investigations of the various retinal pigments.

Application of Artificial Pigments to Structure Determination and Study of Photoinduced Transformations of Retinal Proteins

Lifetimes of stimulus-induced conformations of the phototaxis receptor sensory rhodopsin II (SR-II) from Halobacterium halobium are modulated with seven receptor analogues. By monitoring the receptor dynamics in vitro and physiological responses of the cell in vivo, we observe receptor signaling efficiency increases with decreasing cycling frequency (turnover number) of the receptor. The results demonstrate that modulating lifetimes of protein conformations at the SR-II photoactivation site with chromophore analogues alters the lifetime of the active conformation at the signaling site. We further explore the relationship between photocycle intermediates and the signaling efficiency by analyzing the time-averaged concentrations of the two long-lived spectral intermediates of the SR-II photocycle: S-II350 and S-II530. The results are consistent with the signaling site being activated during formation of S-II350, but not reset by the transition of S-II350 into S-II530; rather deactivation appears to require subsequent decay of S-II530. The results indicate the structural changes at the photoactivation site in the S-II350----S-II530 transition do not reset the signaling site. The procedure used here, applicable in principle to any photoactivated or ligand-activated receptor, provides an initial approach to identify structural alterations key to the receptor activation process.

Identification of signaling states of a sensory receptor by modulation of lifetimes of stimulus-induced conformations: the case of sensory rhodopsin II.

The invention relates to a compound of formula: ##STR1## in which formula: R1 to R4 denote, independently, H, OH, C1 -C6 alkyl or C1 -C6 alkoxy; and A denotes --COR5, R5 being H when at least one of the substituents R1 to R4 is other than H; C1 -C6 alkyl; amino; (C1 -C6)alkylamino; di(C1 -C6) alkylamino; arylamino; benzylamino; amino drived from a cyclic or heterocyclic amine; (--COR5 being able, when it is an amide group, to be the amide group of an amino acid or of a glucosamine); or alternatively R5 denotes --OR6, R6 being H or (C1 -C6)alkyl; C1 -C6 mono- or polyhydroxyalkyl, or aryl or benzyl, both optionally substituted; --OR6 also being able to be derived from a sugar; and the salts and isomers of this compound. The invention also relates to a process for preparing this compound and medicinal and cosmetic compositions containing them.

Naphthalene derivatives having retinoid type action, the process for preparation thereof and medicinal and cosmetic compositions containing them

Prompted by the near infrared-absorbing properties of some of the azulenic bacteriorhodopsin (bR) analogs, we have analyzed their absorption characteristics along with 11 new related ring-fused analogs and the corresponding Schiff bases (SB) and protonated Schiff bases (PSB). The following three factors are believed to contribute to the total red shift of each of the pigment analogs (sigma RS): perturbation of the basic chromophore (SB shift, delta SB), protonation of the SB (PSB shift, PSBS) and protein perturbation (the opsin shift, OS). For each factor, effects of structural modifications were examined. For the red-shifted pigments, percent OS has been suggested as an alternate way of measuring protein perturbation. Computer-simulated chromophores provided evidence against any explanation involving altered shapes of the binding pocket as a major cause for absorption differences. Implications of the current bR results on preparation of further red-shifted bR and possible application to visual pigment analogs are discussed.

Makio Yamada

Papers

Properties of an Analogue Pigment of Bacteriorhodopsin Synthesized with Naphthylretinal