Analog pigment studies of chromophore-protein interactions in metarhodopsins

Abstract

Several analogue pigments have been prepared containing retinals altered at the cyclohexyl ring or proximal to the aldehyde group in order to examine the role of the chromophore in the formation of the metarhodopsin I and II states of visual pigments. Deletion of the 13-methyl group on the isoprenoid chain did not affect metarhodopsin formation. However, analogue pigments containing chromophores with modified rings did not show the typical absorption changes associated with the metarhodopsin transitions of native or regenerated rhodopsins. In particular, 4-hydroxyretinal pigments did not show clear transitions between the metarhodopsin I and metarhodopsin II states. Pigment formed with an acyclic retinal showed no evidence by absorption spectroscopy of metarhodopsin formation. A retinal altered by substitution of a five-membered ring containing a nitroxide required a more acidic pH than the native pigment for formation of the metarhodopsin II state. ESR data suggest that the ring remains buried within the protein through the metarhodopsin II state. However, the Schiff base linkage is susceptible to hydrolysis of hydroxylamine in the metarhodopsin II state. These data indicate that (1), in the transition from rhodopsin to metarhodopsin II, major protein conformational changes are occurring near the lysine-retinal linkage whereas the ring portion of the chromophore remains deeply buried within the protein and (2) pigment absorptions characteristic of the metarhodopsin I and II states may be due to specific protein-chromophore interactions near the region of the chromophore ring.

QUANTUM YIELD OF CHAPSO‐SOLUBILIZED RHODOPSIN and 3‐HYDROXY RETINAL CONTAINING BOVINE OPSIN*

“…Such an assumption was recently verified in studies performed with 4-hydroxy retinal containing opsin. This artificial visual pigment undergoes an altered photochemistry and behaves differently in physiological experiments (Renk and Crouch, 1989;Corson ef al., 1990).…”

“…These results concerning the physiological function of 4-hydroxy retinal in bovine opsin represent one of only a few cases where, besides the absorption maximum and the thermal stability, data of more physiological relevance were collected for visual pigment derivatives (Nelson et al, 1970;Ebrey et al, 1980;Fukada et al, 1982;Yoshizawa and Fukada, 1983;Liu et al, 1986;Ganter et al, 1989;Renk and Crouch, 1989;Corson et al, 1990). In particular, the quantum efficiency for the primary photoreaction is a crucial parameter for the function of a visual pigment.…”

Quantum Mechanical/Molecular Mechanical Structure, Enantioselectivity, and Spectroscopy of Hydroxyretinals and Insights into the Evolution of Color Vision in Small White Butterflies

“…20 Due to the absence of X-ray structure of visual pigments containing A 3 - or A 4 -retinal, such assumptions have so far remained untested. Note that, hydroxylretinals are known to form bleachable visual pigments 25 and are found to be present only in invertebrates. Apparently, theoretical incorporation of hydroxyretinal derivatives into an already available structure of invertebrate pigment is a viable alternative.…”

Transduction noise induced by 4-hydroxy retinals in rod photoreceptors

“…Seeking biochemical probes for the control of discrete wave production at rhodopsin, we have begun to explore the role of retinal in the generation of spontaneous and light-evoked responses (14,15). We began with 4hydroxy analogues of retinal because they are known to form thermally stable and spectrally distinct visual pigments with vertebrate opsin in vitro (16,17), and physiologically functional pigments in invertebrates where 3hydroxy retinal and its 4-hydroxy relative have been found to occur naturally in the visual pigments of insects ( 1 8) and a mollusc (19). These recently discovered retinal analogues are the third and fourth known visual pigment chromophores in the animal kingdom, and the 4-hydroxy analogue has been found to participate along with 1 1-cis retinal and 1 -cis 3,4-dehydro retinal in a unique trichromatic visual system in the squid Watasenia scintillans (19).…”