Inherently tunable electrostatic assembly of membrane proteins

Matter, energy and information network of a graphene-peptide-based fluorescent sensing system for molecular logic computing, detection and imaging of cancer stem cell marker CD133 in cells and tumor tissues

A graphene-peptide-based fluorescent sensing system for molecular logic operations, sensing and imaging of CD133.

Functionally Active Membrane Proteins Incorporated in Mesostructured Silica Films

A versatile synthetic protocol is reported that allows high concentrations of functionally active membrane proteins to be incorporated in mesostructured silica materials. Judicious selections of solvent, surfactant, silica precursor species, and synthesis conditions enable membrane proteins to be stabilized in solution and during subsequent coassembly into silica-surfactant composites with nano- and mesoscale order. This was demonstrated by using a combination of nonionic ( n-dodecyl-β-d-maltoside or Pluronic P123), lipid-like (1,2-diheptanoyl- s n-glycero-3-phosphocholine), and perfluoro-octanoate surfactants under mild acidic conditions to coassemble the light-responsive transmembrane protein proteorhodopsin at concentrations up to 15 wt % into the hydrophobic regions of worm-like mesostructured silica materials in films. Small-angle X-ray scattering, electron paramagnetic resonance spectroscopy, and transient UV-visible spectroscopy analyses established that proteorhodopsin molecules in mesostructured silica films exhibited native-like function, as well as enhanced thermal stability compared to surfactant or lipid environments. The light absorbance properties and light-activated conformational changes of proteorhodopsin guests in mesostructured silica films are consistent with those associated with the native H+-pumping mechanism of these biomolecules. The synthetic protocol is expected to be general, as demonstrated also for the incorporation of functionally active cytochrome c, a peripheral membrane protein enzyme involved in electron transport, into mesostructured silica-cationic surfactant films.

Biopores/membrane proteins in synthetic polymer membranes

BACKGROUND

Mimicking cell membranes by simple models based on the reconstitution of membrane proteins in lipid bilayers represents a straightforward approach to understand biological function of these proteins. This biomimetic strategy has been extended to synthetic membranes that have advantages in terms of chemical and mechanical stability, thus providing more robust hybrid membranes.

SCOPE OF THE REVIEW

We present here how membrane proteins and biopores have been inserted both in the membrane of nanosized and microsized compartments, and in planar membranes under various conditions. Such bio-hybrid membranes have new properties (as for example, permeability to ions/molecules), and functionality depending on the specificity of the inserted biomolecules. Interestingly, membrane proteins can be functionally inserted in synthetic membranes provided these have appropriate properties to overcome the high hydrophobic mismatch between the size of the biomolecule and the membrane thickness.

MAJOR CONCLUSION

Functional insertion of membrane proteins and biopores in synthetic membranes of compartments or in planar membranes is possible by an appropriate selection of the amphiphilic copolymers, and conditions of the self-assembly process. These hybrid membranes have new properties and functionality based on the specificity of the biomolecules and the nature of the synthetic membranes.

GENERAL SIGNIFICANCE

Bio-hybrid membranes represent new solutions for the development of nanoreactors, artificial organelles or active surfaces/membranes that, by further gaining in complexity and functionality, will promote translational applications. This article is part of a Special Issue entitled: Lipid order/lipid defects and lipid-control of protein activity edited by Dirk Schneider.

A Usual G-Protein-Coupled Receptor in Unusual Membranes

G-protein-coupled receptors (GPCRs) are the largest family of membrane-bound receptors and constitute about 50% of all known drug targets. They offer great potential for membrane protein nanotechnologies. We report here a charge-interaction-directed reconstitution mechanism that induces spontaneous insertion of bovine rhodopsin, the eukaryotic GPCR, into both lipid- and polymer-based artificial membranes. We reveal a new allosteric mode of rhodopsin activation incurred by the non-biological membranes: the cationic membrane drives a transition from the inactive MI to the activated MII state in the absence of high [H(+)] or negative spontaneous curvature. We attribute this activation to the attractive charge interaction between the membrane surface and the deprotonated Glu134 residue of the rhodopsin-conserved ERY sequence motif that helps break the cytoplasmic "ionic lock". This study unveils a novel design concept of non-biological membranes to reconstitute and harness GPCR functions in synthetic systems.

Reconstitution of bacteriorhodopsin with cationic poly(dimethylaminoethyl acrylate)-block-poly(methylacrylate) for bio-hybrid materials

A kind of cationic amphiphilic copolymer was synthesized for supporting membrane proteins to prepare bio-hybrid materials.

Interface for Light-Driven Electron Transfer by Photosynthetic Complexes Across Block Copolymer Membranes

Incorporation of membrane proteins into nanodevices to mediate recognition and transport in a collective and scalable fashion remains a challenging problem. We demonstrate how nanoscale photovoltaics could be designed using robust synthetic nanomembranes with incorporated photosynthetic reaction centers (RCs). Specifically, RCs from Rhodobacter sphaeroides are reconstituted spontaneously into rationally designed polybutadiene membranes to form hierarchically organized proteopolymer membrane arrays via a charge-interaction-directed reconstitution mechanism. Once incorporated, the RCs are fully active for prolonged periods based upon a variety of spectroscopic measurements, underscoring preservation of their 3D pigment configuration critical for light-driven charge transfer. This result provides a strategy to construct solar conversion devices using structurally versatile proteopolymer membranes with integrated RC functions to harvest broad regions of the solar spectrum.

"Frozen" block copolymer nanomembranes with light-driven proton pumping performance

Cellular membranes are natural nanoengineering devices, where matter transport, information processing, and energy conversion across the nanoscale boundaries are mediated by membrane proteins (MPs). Despite the great potential of MPs for nanotechnologies, their broad utility in engineered systems is limited by the fluidic and often labile nature of MP-supporting membranes. Little is known on how to direct spontaneous reconstitution of MPs into robust synthetic nanomembranes or how to tune MP functions through rational design of these membranes. Here we report that proteorhodopsin (PR), a light-driven proton pump, can be spontaneously reconstituted into "frozen" (i.e., glassy state) amphiphilic block copolymer membranes via a charge-interaction-directed reconstitution mechanism. We show that PR is not enslaved by a fluidic or lipid-based membrane environment. Rather, well-defined block copolymer nanomembranes, with their tunable membrane moduli, act as allosteric regulators to support the structural integrity and function of PR. Versatile membrane designs exist to modulate the conformational energetics of reconstituted MPs, therefore optimizing proteomembrane stability and performance in synthetic systems.

Green proteorhodopsin reconstituted into nanoscale phospholipid bilayers (nanodiscs) as photoactive monomers

Over 4000 putative proteorhodopsins (PRs) have been identified throughout the oceans and seas of the Earth. The first of these eubacterial rhodopsins was discovered in 2000 and has expanded the family of microbial proton pumps to all three domains of life. With photophysical properties similar to those of bacteriorhodopsin, an archaeal proton pump, PRs are also generating interest for their potential use in various photonic applications. We perform here the first reconstitution of the minimal photoactive PR structure into nanoscale phospholipid bilayers (nanodiscs) to better understand how protein-protein and protein-lipid interactions influence the photophysical properties of PR. Spectral (steady-state and time-resolved UV-visible spectroscopy) and physical (size-exclusion chromatography and electron microscopy) characterization of these complexes confirms the preparation of a photoactive PR monomer within nanodiscs. Specifically, when embedded within a nanodisc, monomeric PR exhibits a titratable pK(a) (6.5-7.1) and photocycle lifetime (∼100-200 ms) that are comparable to the detergent-solubilized protein. These ndPRs also produce a photoactive blue-shifted absorbance, centered at 377 or 416 nm, that indicates that protein-protein interactions from a PR oligomer are required for a fast photocycle. Moreover, we demonstrate how these model membrane systems allow modulation of the PR photocycle by variation of the discoidal diameter (i.e., 10 or 12 nm), bilayer thickness (i.e., 23 or 26.5 Å), and degree of saturation of the lipid acyl chain. Nanodiscs also offer a highly stable environment of relevance to potential device applications.

Photochemical and thermal stability of green and blue proteorhodopsins: implications for protein-based bioelectronic devices

The photochemical and thermal stability of the detergent-solubilized blue- and green-absorbing proteorhodpsins, BPR and GPR, respectively, are investigated to determine the viability of these proteins for photonic device applications. Photochemical stability is studied by using pulsed laser excitation and differential UV-vis spectroscopy to assign the photocyclicity. GPR, with a cyclicity of 7 × 10(4) photocycles protein(-1), is 4-5 times more stable than BPR (9 × 10(3) photocycles protein(-1)), but is less stable than native bacteriorhodopsin (9 × 10(5) photocycles protein(-1)) or the 4-keto-bacteriorhodopsin analogue (1 × 10(5) photocycles protein(-1)). The thermal stabilities are assigned by using differential scanning calorimetry and thermal bleaching experiments. Both proteorhodopsins display excellent thermal stability, with melting temperatures above 85 °C, and remain photochemically stable up to 75 °C. The biological relevance of our results is also discussed. The lower cyclicity of BPR is found to be adequate for the long-term biological function of the host organism at ocean depths of 50 m or more.