title: Time-resolved resonance Raman analysis of chromophore structural changes in the formation and decay of rhodopsin's BSI intermediate.
abstract: Time-resolved resonance Raman microchip flow experiments are performed to obtain the vibrational spectrum of the chromophore in rhodopsin's BSI intermediate and to probe structural changes in the bathorhodopsin-to-BSI and BSI-to-lumirhodopsin transitions. Kinetic Raman spectra from 250 ns to 3 micros identify the key vibrational features of BSI. BSI exhibits relatively intense HOOP modes at 886 and 945 cm(-1) that are assigned to C(14)H and C(11)H=C(12)H A(u) wags, respectively. This result suggests that in the bathorhodopsin-to-BSI transition the highly strained all-trans chromophore has relaxed in the C(10)-C(11)=C(12)-C(13) region, but is still distorted near C(14). The low frequency of the 11,12 A(u) HOOP mode in BSI compared with that of lumirhodopsin and metarhodopsin I indicates weaker coupling between the 11H and 12H wags due to residual distortion of the BSI chromophore near C(11)=C(12). The C=NH(+) stretching mode in BSI at 1653 cm(-1) exhibits a normal deuteriation induced downshift of 23 cm(-1), implying that there is no significant structural rearrangement of the Schiff base counterion region in the transition of bathorhodopsin to BSI. However, a dramatic Schiff base environment change occurs in the BSI-to-lumirhodopsin transition, because the 1638 cm(-1) C=NH(+) stretching mode in lumirhodopsin is unusually low and shifts only 7 cm(-1) in D(2)O, suggesting that it has essentially no H-bonding acceptor. With these data we can for the first time compare and discuss the room temperature resonance Raman vibrational structure of all the key intermediates in visual excitation.
authors.affiliation: Department of Chemistry, University of California, Berkeley, California 94720, USA.
authors.forename: Duohai
authors.initials: D
authors.lastname: Pan
authors.forename: Ziad
authors.initials: Z
authors.lastname: Ganim
authors.forename: Judy E
authors.initials: JE
authors.lastname: Kim
authors.forename: Michiel A
authors.initials: MA
authors.lastname: Verhoeven
authors.forename: Johan
authors.initials: J
authors.lastname: Lugtenburg
authors.forename: Richard A
authors.initials: RA
authors.lastname: Mathies
mesh_terms: D000818:Animals; D002417:Cattle; D007700:Kinetics; D008958:Models, Molecular; D010777:Photochemistry; D011487:Protein Conformation; D012243:Rhodopsin / Q000031:analogs & derivatives* / Q000737:chemistry*; D013059:Spectrum Analysis, Raman / Q000379:methods
chemical_list: C018586:lumirhodopsin; C015017:bathorhodopsin; D012243:Rhodopsin