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.

Green Proteorhodopsin Reconstituted into Nanoscale Phospholipid Bilayers (Nanodiscs) as Photoactive Monomers

“…A second requirement is tailoring the photophysical properties of ndPRs for specific applications, such as holography, 12 binary optical memories, 80 and security inks 81 among others. We show that altering the particle dimensions, via the disk diameter or bilayer composition, modulates the PR photocycle.…”

“…3–7 These proteins are identified solely from genetic analysis of coastal and oceanic water samples and no native host has yet been cultivated. 4,8 Hence, PRs are often expressed in Escherichia coli and solubilized in various detergents 9–12 or reconstituted in phospholipid environments 13–16 to stabilize the protein prior to investigation.…”

Photochromic Bacteriorhodopsin Mutant with High Holographic Efficiency and Enhanced Stability via a Putative Self-Repair Mechanism

“…46 When the observed and calculated data are compared, the Kogelnik theory is often found to overestimate the actual performance by roughly 20%. 46,47 …”

Determining the Oligomeric Structure of Proteorhodopsin by Gd3+-Based Pulsed Dipolar Spectroscopy of Multiple Distances

“…The cysteine mutations have been shown to not affect overall function (Dioumaev et al, 2003;Krebs et al, 2002;Stone et al, 2013). Further mutagenesis modified the glutamic acid at residue 108 to a glutamine, which extends the M-intermediate state of the photocycle by eliminating a proton acceptor site (Dioumaev et al, 2003;Xi et al, 2008), it but is not expected to affect the oligomer structure. Single cysteine mutations were introduced in the proteins at residues Trp58, and Thr177.…”

“…Although the functional implications of this assembly are still being investigated, few precise details of the G-PR oligomer structure are currently available. A recent crystal structure (Ran et al, 2013) reveals a doughnutshaped hexameric assembly for blue-absorbing proteorhodopsin (B-PR), a protein that is homologous to G-PR but differs in its maximum absorption wavelength and photocycle timescale (Hillebrecht et al, 2006;Xi et al, 2008). However, in G-PR hexamers, there has been only a single measurement of a short interprotein distance, which identified a radial orientation of the protein within the hexamer (Stone et al, 2013).…”