ISSN:0021-2148    

DOI:10.1002/ijch.199500026

出版商:WILEY‐VCH Verlag    

年代:1995

数据来源: WILEY

摘要:

AbstractThe past few years have been an exciting period in the field of the structure of retinal proteins, especially the visual pigments. A significant achievement is the 9 Å projection map of bovine rhodopsin. This not only provides knowledge of the three‐dimensional structure of visual pigments, but also establishes a more reliable basis for the structural modeling of all the G‐protein‐coupled receptors. The modeling of such three‐dimensional structures will eventually lead to a better understanding of the function of visual pigments and other G‐protein‐coupled receptors. Our goal in this article is to draw attention to recent developments in the structure of retinal proteins, with special emphasis on visual pigments. By combining a wide range of existing experimental data with the results of theoretical calculations, a new three‐dimensional structure of visual pigments, which differs from the models which have so far been reporte

ISSN:0021-2148    

DOI:10.1002/ijch.199500027

出版商:WILEY‐VCH Verlag    

年代:1995

数据来源: WILEY

摘要:

AbstractRecent advances in laser technology now allow us to study the ultrafast primary photochemical events in rhodopsin, bacteriorhodopsin, and halorhodopsin in real time. The results of various ultrafast studies of rhodopsins are reviewed with an emphasis on (1) the relationship between the reaction rate and reaction efficiency and its implications for the mechanism of isomerization, (2) the homogeneity of the reaction pathways, and (3) the role of the protein in the reaction dynamics. The results mandate the introduction of a new paradigm to describe these ultrafast reactions that specifically considers the importance of the timescale of vibrational dephasing and relaxation relative to the reactive motion and the contribution of vibrational coherence to the reaction mechanism.

ISSN:0021-2148    

DOI:10.1002/ijch.199500028

出版商:WILEY‐VCH Verlag    

年代:1995

数据来源: WILEY

摘要:

AbstractRaman spectroscopic studies on photoreactive retinal proteins are comprehensively described, including the basic physics of Raman scattering and illustrative examples of the types of information on the structure and function of the retinal chromophore and its environment which can be obtained from the vibrational Raman spectra. In addition, practical advice and recipes are given which should enable the reader to plan and eventually perform a Raman experiment in a photolabile retinal protein. A dominant role is played by the resonance Raman (RR) experiment with visible laser excitation which selectively probes the retinal chromophore. Much discussion is devoted to bacteriorhodopsin (bR) and its photocycle as a paradigm for a light‐induced reaction of a retinal protein. Various time‐resolved techniques are described to study the temporal evolution of the bR chromophore by probing RR spectra of intermediate states. Vibrational Raman spectra are interpreted in terms of structure and structural changes of the chromophore. RR spectroscopic studies on halorhodopsin, sensory rhodopsin, and visual pigments are reported, as well as on modified proteins in which retinal analogues are incorporated, and on site‐specific mutants. Results of ultraviolet RR experiments which selectively probe the aromatic side chains in the protein backbone are reported. In addition, a promising new technique of near‐infrared Raman excitation is discussed. Finally, application of coherent anti‐Stokes Raman spectroscopy (CARS) to retinal proteins is

ISSN:0021-2148    

DOI:10.1002/ijch.199500029

出版商:WILEY‐VCH Verlag    

年代:1995

数据来源: WILEY

摘要:

AbstractThe 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 theChlamydomonasphotoreceptor 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 retin

ISSN:0021-2148    

DOI:10.1002/ijch.199500030

出版商:WILEY‐VCH Verlag    

年代:1995

数据来源: WILEY

摘要:

AbstractThe application of NMR spectroscopy to the retinal proteins bacteriorhodopsin (BR) and rhodopsin is reviewed.2H‐,15N‐, and13C‐solid‐state NMR spectroscopy have contributed considerably to understanding the conformation and chemical environment of the protonated retinylidene Schiff base in BR as well as in rhodospin. The data from both pigments clarified the mechanism of the opsin shift which is quite different for rhodopsin and BR. An analysis of the chemical shifts of isotopically labeled aspartic acid, tyrosine, and proline incorporated into BR‐provided evidence for the protonation state of Asp and Tyr, and the isomerization state of the Xaa—Pro peptide bond, respectively. Solid‐state NMR spectroscopy was also applied to the investigation of the photocycle intermediates of BR, as well as bathorhodopsin and metarhodopsin II, which are formed after light‐activation of rhodopsin. Solution NMR spectroscopy of BR solubilized in detergents or organic solvents, as well as of opsin‐derived peptide segments, was also applied to the investigation of the two‐ and three‐dimens

ISSN:0021-2148    

DOI:10.1002/ijch.199500031

出版商:WILEY‐VCH Verlag    

年代:1995

数据来源: WILEY

摘要:

AbstractThe literature describing intermediates formed after photolysis of visual pigments is reviewed. Results obtained near physiological temperatures using time‐resolved optical density measurements in the UV/Vis region are emphasized. The general character of intermediates which appear in the course of protein function, and the role of methods with different time resolutions in their study, are discussed. Specific results for intermediates from bathorhodopsin to metarhodopsin II are treated in detail, with limited discussion of the earlier and later species. The discussion centers on the best‐understood pigment, bovine rhodopsin, but results for cone‐type and invertebrate pigments are also discussed. Comparison is made between the picture of the intermediates obtained using low‐temperature trapping methods and that obtained using kinetic measurements. The thermodynamic parameters of the intermediates are discussed, and their significance for the structure/function of heptahelical protein intermediates in general is con

ISSN:0021-2148    

DOI:10.1002/ijch.199500032

出版商:WILEY‐VCH Verlag    

年代:1995

数据来源: WILEY

摘要:

AbstractExperiments are reviewed in which the photoreactions of the visual pigments rhodopsin and octopus rhodopsin have been investigated by FTIR spectroscopy. It is shown that from the spectra important characteristic structural elements can be derived for the dark state as well as for the intermediates. Since the spectra contain contributions from the chromophore as well as from the protein, methods are described which allow one to discriminate between them. In the case of rhodopsin, the influence of single amino acids on spectra and function is assessed by investigations of specific mutants. The role of the chromophore‐protein interaction for the photoreaction and the activation mechanism is addressed by studies of modified rhodopsins containing retinal analogues as chromophores. Characteristics of the active state, which is capable of transducin activation, are especially emphasize

ISSN:0021-2148    

DOI:10.1002/ijch.199500033

出版商:WILEY‐VCH Verlag    

年代:1995

数据来源: WILEY

摘要:

AbstractA variety of spectroscopic and biochemical studies of recombinant site‐directed mutants of rhodopsin and related visual pigments have been carried out. These studies have elucidated key structural elements common to visual pigments, such as a conserved disulfide bond. In addition, systematic analysis of the chromophore‐binding pocket in rhodopsin and cone pigments has led to an improved understanding of the mechanism of the opsin‐shift, and of particular molecular determinants underlying color vision in humans. Identification of conformational changes which occur upon rhodopsin photoactivation has been of particular recent concern. Assignment of these molecular alterations to specific regions in the receptor has been attempted by studying native opsin regenerated with synthetic retinal analogues or recombinant opsins regenerated with 11‐cis‐retinal. Individual molecular groups that undergo structural alterations during photoactivation have been identified. Analysis of particular mutant pigments in which specific groups are locked into their respective “on” or “off” states has provided a framework to identify determinants of the active conformation as well as the minimal number of intramolecular transitions required to switch between inactive and active conformations. A simple model for the active state of rhodopsin can be compared to structural models of its ground state to localize chromophore‐protein interactions that may be important in the photoa

ISSN:0021-2148    

DOI:10.1002/ijch.199500034

出版商:WILEY‐VCH Verlag    

年代:1995

数据来源: WILEY

摘要:

AbstractAftercis/transisomerization of retinal and early photoproducts, activated rhodopsin (R*) develops signaling states for different proteins in a time‐ordered sequence. Rhodopsin kinase binds all Meta forms, including the early Meta I, while interaction with transducin (Gt) or arrestin requires the deprotonated Schiff base form, Meta II (MII). Gtrecognizes a specific conformation, termed MIIb, which arises from an additional, spectrally silent conversion, linked to proton uptake. Collisional coupling with the GDP‐bound Gtholoprotein induces the release of GDP and formation of a stable R*—Gtcomplex, in which the nucleotide binding site of Gtis empty. The empty site complex, once formed, remains stable, even if the retinal is re‐isomerized to thecisconfiguration. The cytoplasmic surface of rhodopsin appears to provide the majority of interaction sites for other proteins. Physical analyses and mutagenesis have emphasized the loops connecting helices C/D and E/F of the seven‐helix structure. Any interaction between R* and Gtdepends on a conserved charge pair at the interface between the helix C and the adjacent loop CD. Replacements or deletions in loops CD and EF were found to cause more specific functional defects, including slow release of GDP or failure of GTP‐induced complex dissociation. In the dark, signaling states with low activity can be generated by reversible binding of all‐trans‐retinal to opsin. These light‐independent signaling states are different fr

ISSN:0021-2148    

DOI:10.1002/ijch.199500035

出版商:WILEY‐VCH Verlag    

年代:1995

数据来源: WILEY