(5‐demethyl)‐Bacteriorhodopsin analogue: its formation and light‐driven proton pump action

Abstract

The binding of the isomers fall-trans, tfcis, f f-c& and 94s) of ~~~~~t~~lr~t~~~ to ~~~t~~i~o~~~~ and the light-dark adaptation as well as the tight-driven proton pump action of the resulting bacteriorhodopsin analogue were studied. The (Sdemethyl)-bacteriorhodopsin is formed -3-times faster than unmodified bacteriorhodopsin and shows an efficient light-driven proton pump action. These findings show that upon binding of retinal to bacterioopsin the protein forces the chromophore to adopt a more planar ring-chain conformation than in free retinal.~~obacterium hatobium &r@e mernb~~e Proton pumpChromoproteins with a retinylidene chromophore such as bacteriorhodapsin, visual pigments and retinochrome, play an important role in photobiology [I]. Bacteriorhodopsin (hereafter bR), the light energy converting protein of the purple membrane of the halo~hili~ microorganism Iiutobucreriwn halobium, occurs in a light-(Amax = 570 nm) and in a dark-adapted form (hmBX = 560 nm) [2]* The chromophore of the lightadapted form is an all-irons retinylidene moiety. In the dark-adapted form a 1: 1 ~~~ibrium between 13-t& and all-Pans isomers exists [Z].retinal does not bind to bO [Ltf* In continuation of our study on the effect of the different methy groups in retinal upon the binding properties and the light-driven proton pump action of bR [7], we now report on the binding properties of 5-demethyiretinai ( fig. 1) (in its dl-trans, 13-c&, 1 I-& and 9-c& form) to bO. The light-dark adaptation together with the light-driven proton pump action of (%demethyl)-bR are also discussed. 2, MATERIALS AND METHODS The

Retinal β-Ionone Ring–Salinixanthin Interactions in Xanthorhodopsin: A Study Using Artificial Pigments

“…We found that the presence of a methyl group at position C 5 or the methyls at C 1 is crucial for the ring orientation and locking the retinal chromophore in a conformation that allows formation of the chromophore–protein covalent bond. In analogy to bR, the methyl at position 1 or 5 is probably required for specific retinal–protein interactions that induce a ring–chain retinal planar conformation within its binding site. , The phenylretinal that does not bear any bulky groups and has a planar conformation is able to form a covalent bond with Lys-240, even though it lacks the crucial methyl group at position C 5 . It is evident that its ability to form a stable pigment does not correlate with its relatively small size in the ring area, as the linear analogue that lacks the ring did not form a pigment.…”

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

“…Removal of the 5-methyl (12, R = H) produces a pigment which is reported to reduce the proton-pumping efficiency by 40%. 18 The 5-ethyl (12, R = Et) and 5-methoxy (12, R = OMe) retinals form stable pigments which exhibit some proton-pumping activity.'? 5-Bromo-bR (containing 12, R =Br, as chromophore) has only 11% of the proton-pumping activity of bR,20 whereas the blue-shifted 5-trifluoromethyl-bR (12, R =CF 3 , "' max 465 nm) is nonfunctional."…”