title: Evaluation of blue and green absorbing proteorhodopsins as holographic materials.
abstract: Transient holographic diffraction is observed for the green (GPR) and blue (BPR) absorbing proteorhodopsins (BAC31A8 and HOT75M1, respectively), as well as the GPR E108Q and BPR E110Q variants. In contrast to bacteriorhodopsin, where the metastable bR-M pair is responsible for generating diffraction, the pR and red-shifted N-like states fulfill that role in both the green and blue wild-type proteorhodopsins. The GPR E108Q and BPR E110Q variants, however, behave more similarly to their bacteriorhodopsin analogue, D96N, with diffraction arising from the PR M-state (strongly enhanced in both GPR E108Q and BPR E110Q). Of the four proteins evaluated, wild type (WT) GPR and GPR E108Q produce the highest diffraction efficiencies, etamax, at approximately 1% for a 1.7 OD sample. GPR E108Q, however, requires 1-2 orders of magnitude less laser intensity to generate eta equivalent to WT GPR and BR D96N under similar conditions (as compared to literature values). WT BPR requires lower actinic powers than GPR but diffracts only about 30% as well. BPR E110Q performs the most poorly of the four, with etamax < 0.05% for a 1.4 OD film. The Kramers-Kronig transformation and Koglenik's coupled wave theory were used to predict the dispersion spectra and diffraction efficiency for the long M-state variants. To a first approximation, the gratings formed by all samples decay upon discontinuing the 520 nm actinic beams with a time constant characteristic of the appropriate intermediate: the N-like state for WT GPR and BPR and the M-state for GPR 108Q and BPR E110Q.
authors.affiliation: W.M. Keck Center for Molecular Electronics, Department of Chemistry, Syracuse University, Syracuse, New York 13244, USA.
authors.forename: Bangwei
authors.initials: B
authors.lastname: Xi
authors.forename: William C
authors.initials: WC
authors.lastname: Tetley
authors.forename: Duane L
authors.initials: DL
authors.lastname: Marcy
authors.forename: Cheng
authors.initials: C
authors.lastname: Zhong
authors.forename: Gregg
authors.initials: G
authors.lastname: Whited
authors.forename: Robert R
authors.initials: RR
authors.lastname: Birge
authors.forename: Jeffrey A
authors.initials: JA
authors.lastname: Stuart
mesh_terms: D000042:Absorption; D003116:Color; D006696:Holography / Q000379:methods*; D012243:Rhodopsin / Q000737:chemistry*; D025604:Rhodopsins, Microbial
chemical_list: D025604:Rhodopsins, Microbial; C413548:proteorhodopsin; D012243:Rhodopsin