All-trans/13-cis isomerization of retinal is required for phototaxis signaling by sensory rhodopsins in Halobacterium halobium.
An analogue of all-trans retinal in which all-trans/13-cis isomerization is blocked by a carbon bridge from C12 to C14 was incorporated into the apoproteins of sensory rhodopsin I (SR-I) and sensory rhodopsin II (SR-II, also called phoborhodopsin) in retinal-deficient Halobacterium halobium membranes. The "all-trans-locked" retinal analogue forms SR-I and SR-II analogue pigments with similar absorption spectra as the native pigments. Blocking isomerization prevents the formation of the long-lived intermediate of the SR-I photocycle (S373) and those of the SR-II photocycle (S-II360 and S-II530). A computerized cell tracking and motion analysis system capable of detecting 2% of native pigment activity was used for assessing motility behavior. Introduction of the locked analogue into SR-I or SR-II apoprotein in vivo did not restore phototactic responses through any of the three known photosensory systems (SR-I attractant, SR-I repellent, or SR-II repellent). We conclude that unlike the phototaxis receptor of Chlamydomonas reinhardtii, which has been reported to mediate physiological responses without specific double-bond isomerization of its retinal chromophore (Foster et al., 1989), all-trans/13-cis isomerization is essential for SR-I and SR-II phototaxis signaling.
Yan
B
B
Department of Chemistry, Columbia University, New York 10027.
Takahashi
T
T
Johnson
R
R
Derguini
F
F
Nakanishi
K
K
Spudich
J L
JL
D019843:Archaeal Proteins; D001436:Bacteriorhodopsins / Q000378:metabolism*; D002338:Carotenoids; D002465:Cell Movement; D006217:Halobacterium / Q000378:metabolism / Q000502:physiology*; D025602:Halorhodopsins; D007536:Isomerism; D007700:Kinetics; D008027:Light; D010777:Photochemistry; D012172:Retinaldehyde / Q000378:metabolism*; D012176:Retinoids / Q000378:metabolism*; D025603:Sensory Rhodopsins; D015398:Signal Transduction; D013053:Spectrophotometry
D019843:Archaeal Proteins; D025602:Halorhodopsins; D012176:Retinoids; C061497:SRI protein, Halobacterium; D025603:Sensory Rhodopsins; C061508:sensory rhodopsin II protein, archaeal; D002338:Carotenoids; D001436:Bacteriorhodopsins; D012172:Retinaldehyde