title: Time-resolved WAXS reveals accelerated conformational changes in iodoretinal-substituted proteorhodopsin.
abstract: Time-resolved wide-angle x-ray scattering (TR-WAXS) is an emerging biophysical method which probes protein conformational changes with time. Here we present a comparative TR-WAXS study of native green-absorbing proteorhodopsin (pR) from SAR86 and a halogenated derivative for which the retinal chromophore has been replaced with 13-desmethyl-13-iodoretinal (13-I-pR). Transient absorption spectroscopy differences show that the 13-I-pR photocycle is both accelerated and displays more complex kinetics than native pR. TR-WAXS difference data also reveal that protein structural changes rise and decay an order-of-magnitude more rapidly for 13-I-pR than native pR. Despite these differences, the amplitude and nature of the observed helical motions are not significantly affected by the substitution of the retinal's C-20 methyl group with an iodine atom. Molecular dynamics simulations indicate that a significant increase in free energy is associated with the 13-cis conformation of 13-I-pR, consistent with our observation that the transient 13-I-pR conformational state is reached more rapidly. We conclude that although the conformational trajectory is accelerated, the major transient conformation of pR is unaffected by the substitution of an iodinated retinal chromophore.
authors.affiliation: Department of Chemistry, Biochemistry and Biophysics, University of Gothenburg, Gothenburg, Sweden.
authors.forename: Erik
authors.initials: E
authors.lastname: Malmerberg
authors.forename: Ziad
authors.initials: Z
authors.lastname: Omran
authors.forename: Jochen S
authors.initials: JS
authors.lastname: Hub
authors.forename: Xuewen
authors.initials: X
authors.lastname: Li
authors.forename: Gergely
authors.initials: G
authors.lastname: Katona
authors.forename: Sebastian
authors.initials: S
authors.lastname: Westenhoff
authors.forename: Linda C
authors.initials: LC
authors.lastname: Johansson
authors.forename: Magnus
authors.initials: M
authors.lastname: Andersson
authors.forename: Marco
authors.initials: M
authors.lastname: Cammarata
authors.forename: Michael
authors.initials: M
authors.lastname: Wulff
authors.forename: David
authors.initials: D
authors.lastname: van der Spoel
authors.forename: Jan
authors.initials: J
authors.lastname: Davidsson
authors.forename: Alexandre
authors.initials: A
authors.lastname: Specht
authors.forename: Richard
authors.initials: R
authors.lastname: Neutze
mesh_terms: D003116:Color; D007455:Iodine / Q000737:chemistry; D007536:Isomerism; D008958:Models, Molecular; D011487:Protein Conformation; D012172:Retinaldehyde / Q000737:chemistry*; D012243:Rhodopsin / Q000737:chemistry*; D025604:Rhodopsins, Microbial; D013816:Thermodynamics; D013997:Time Factors; D014961:X-Ray Diffraction
chemical_list: D025604:Rhodopsins, Microbial; C413548:proteorhodopsin; D012243:Rhodopsin; D007455:Iodine; D012172:Retinaldehyde