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          Institute: MPI für bioanorganische Chemie     Collection: MPI für bioanorganische Chemie     Display Documents

ID: 715714.0, MPI für bioanorganische Chemie / MPI für bioanorganische Chemie
Rhodopsins carrying modified chromophores - the 'making of', structural modelling and their light-induced reactivity.
Authors:Ockenfels, Andreas; Schapiro, Igor; Gärtner, Wolfgang
Date of Publication (YYYY-MM-DD):2016
Title of Journal:Photochemical & Photobiological Sciences
Journal Abbrev.:Photochem.Photobiol.Sci.
Issue / Number:2
Start Page:297
End Page:308
Review Status:Internal review
Audience:Experts Only
Abstract / Description:A series of vitamin-A aldehydes (retinals) with modified alkyl group substituents (9-demethyl-, 9-ethyl-, 9-isopropyl-, 10-methyl, 10-methyl-13-demethyl-, and 13-demethyl retinal) was synthesized and their 11-cis isomers were used as chromophores to reconstitute the visual pigment rhodopsin. Structural changes were selectively introduced around the photoisomerizing C11[double bond, length as m-dash]C12 bond. The effect of these structural changes on rhodopsin formation and bleaching was determined. Global fit of assembly kinetics yielded lifetimes and spectral features of the assembly intermediates. Rhodopsin formation proceeds stepwise with prolonged lifetimes especially for 9-demethyl retinal (longest lifetime tau3 = 7500 s, cf., 3500 s for retinal), and for 10-methyl retinal (tau3 = 7850 s). These slowed-down processes are interpreted as either a loss of fixation (9dm) or an increased steric hindrance (10me) during the conformational adjustment within the protein. Combined quantum mechanics and molecular mechanics (QM/MM) simulations provided structural insight into the retinal analogues-assembled, full-length rhodopsins. Extinction coefficients, quantum yields and kinetics of the bleaching process (mus-to-ms time range) were determined. Global fit analysis yielded lifetimes and spectral features of bleaching intermediates, revealing remarkably altered kinetics: whereas the slowest process of wild-type rhodopsin and of bleached and 11-cis retinal assembled rhodopsin takes place with lifetimes of 7 and 3.8 s, respectively, this process for 10-methyl-13-demethyl retinal was nearly 10 h (34670 s), coming to completion only after ca. 50 h. The structural changes in retinal derivatives clearly identify the precise interactions between chromophore and protein during the light-induced changes that yield the outstanding efficiency of rhodopsin.
Comment of the Author/Creator:Date: 2016, 2016-Feb-10
External Publication Status:published
Document Type:Article
Communicated by:N. N.
Affiliations:MPI für bioanorganische Chemie
Identifiers:ISI:26860474 [ID No:1]
ISSN:1474-9092 [ID No:2]
DOI:10.1039/c5pp00322a [ID No:3]
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