The large multiprotein complex, photosystem I (PSI), which is at the heart of light-dependent reactions in photosynthesis, is integrated as the active component in a solid-state organic photovoltaic cell. These experiments demonstrate that photoactive megadalton protein complexes are compatible with solution processing of organic-semiconductor materials and operate in a dry non-natural environment that is very different from the biological membrane.

Complexation of biomacromolecules (e.g., nucleic acids, proteins, or viruses) with surfactants containing flexible alkyl tails, followed by dehydration, is shown to be a simple generic method for the production of thermotropic liquid crystals. The anhydrous smectic phases that result exhibit biomacromolecular sublayers intercalated between aliphatic hydrocarbon sublayers at or near room temperature. Both this and low transition temperatures to other phases enable the study and application of thermotropic liquid crystal phase behavior without thermal degradation of the biomolecular components.L iquid crystals (LCs) play an important role in biology because their essential characteristic, the combination of order and mobility, is a basic requirement for self-organization and structure formation in living systems (1-3). Thus, it is not surprising that the study of LCs emerged as a scientific discipline in part from biology and from the study of myelin figures, lipids, and cell membranes (4). These and the LC phases formed from many other biomolecules, including nucleic acids (5, 6), proteins (7,8), and viruses (9, 10), are classified as lyotropic, the general term applied to LC structures formed in water and stabilized by the distinctly biological theme of amphiphilic partitioning of hydrophilic and hydrophobic molecular components into separate domains. However, the principal thrust and achievement of the study of LCs has been in the science and application of thermotropic materials, structures, and phases in which molecules that are only weakly amphiphilic exhibit LC ordering by virtue of their steric molecular shape, flexibility, and/or weak intermolecular interactions [e.g., van der Waals and dipolar forces (11)]. These characteristics enable thermotropic LCs (TLCs) to adopt a wide variety of exotic phases and to exhibit dramatic and useful responses to external forces, including, for example, the electro-optic effects that have led to LC displays and the portable computing revolution. This general distinction between lyotropic LCs and TLCs suggests there may be interesting possibilities in the development of biomolecular or bioinspired LC systems in which the importance of amphiphilicity is reduced and the LC phases obtained are more thermotropic in nature. Such biological TLC materials are very appealing for several reasons. Most biomacromolecules were extensively characterized in aqueous environments, but in TLC phases, their solvent-free properties and functions could be investigated in a state in which no or only traces of water are present. Water exhibits a high dielectric constant and has the ability to form hydrogen bonds, greatly influencing the structure and functions of biomacromolecules or compromising electronic properties such as charge transport (12-15). Indeed, anhydrous TLC systems containing glycolipids (16-19), ferritin (20), and polylysine have been reported (21-23). However, a general approach to fabricating TLCs based on nucleic acids, polypeptides, proteins, and protein assemblies of larg...

a b s t r a c tOne of the barriers to the development of protein therapeutics is effective delivery to mammalian cells. The proteins must maintain a careful balance of polar moieties to enable administration and distribution and hydrophobic character to minimize cell toxicity. Numerous strategies have been applied to this end, from appending additional cationic peptides to supercharging the protein itself, sometimes with limited success. Here we present a strategy that combines these methods, by equipping a protein with supercharged elastin-like polypeptide (ELP) tags. We monitored cellular uptake and cell viability for GFP reporter proteins outfitted with a range of ELP tags and demonstrated enhanced uptake that correlates with the number of positive charges, while maintaining remarkably low cytotoxicity and resistance to degradation in the cell. GFP uptake proceeded mainly through caveolae-mediated endocytosis and we observed GFP emission inside the cells over extended time (up to 48 h). Low toxicity combined with high molecular weights of the tag opens the way to simultaneously optimize cell uptake and pharmacokinetic parameters. Thus, cationic supercharged ELP tags show great potential to improve the therapeutic profile of protein drugs leading to more efficient and safer biotherapeutics.

or traditional organic liquid crystals. Therefore, the development of a general strategy for fabricating solvent-free ELP fl uids (liquid crystals and liquids) is an attractive goal.Genetic engineering as a recombinant protein synthesis technology affords a powerful tool for the synthesis of ELPs with predictable properties and biofunctionality. Engineered ELPs allow fabrication of desired sequences with high molecular weights combined with monodispersity, well-defi ned structures and chain lengths that are impossible to be achieved by chemical synthesis. [31][32][33] We demonstrate here the creation of genetically engineered ELPs based on the common pentameric repeat sequence (VPG X G) n found in tropoelastin by taking advantage of the fl exibility of the amino acid composition at the fourth position of that peptide motif. First, glutamic acid was introduced at this site of the repeat to transform the ELPs into supercharged polypeptides (SUPs, (VPG E G) n ). Then, green fl uorescent protein (GFP) was fused to the SUP for an additional level of functionality. Thus, a series of GFP-SUPs (GFP-(VPG E G) n ) with negative charges ranging from 9, over 18, 36, 72 to 144 (GFP-E9, GFP-E18, GFP-E36, GFP-E72, and GFP-E144) were expressed in E. coli (details in Figure S1-S3, Supporting Information). The purity and molecular weights of the products were confi rmed by polyacrylamide gel electrophoresis and matrix-assisted laser desorption/ionization time-of-fl ight mass spectrometry, respectively ( Figure S4 and S5, Supporting Information). Subsequently, the GFP-SUPs were complexed with cationic surfactants. This was inspired by previous work dealing with polyelectrolyte-surfactant complexation via electrostatic interactions. [34][35][36][37][38] In the context of proteins, complexation between cationized ferritin and anionic polymer surfactants yielded mesophases with a narrow temperature range. [ 37 ] Here we propose that the combination of negatively charged GFP-SUP with positively charged surfactants, followed by dehydration, can act as a simple generic scheme for producing solventfree GFP-SUP fl uids. In the present experiments, electrostatic interactions as the driving force couple these GFP-SUPs and surfactants into hybrid lamellar assemblies ( Figure 1 ), where the fl exible alkyl chains of surfactants suppress crystallization. [ 34,35 ] The anhydrous SUP-surfactant complexes exhibit non-Newtonian (smectic liquid crystal) and Newtonian (isotropic liquid) fl uid behaviors. The lengths of the SUP and surfactant are found to be extremely important in tuning the physical properties of the fl uids. We fi nd a high elasticity in the SUP mesophases when they are ordered in smectic layers. The elastic moduli of these phases are larger than the ones reported Biologically inspired peptide-based materials are of increasing interest for applications where biological function and structure are used outside of the natural context. [1][2][3][4][5][6][7][8][9][10] Among them, a specifi c class of repetitive polypeptides termed elasti...

Interfacing proteins with electrode surfaces is important for the field of bioelectronics. Here, a general concept based on phage display is presented to evolve small peptide binders for immobilizing and orienting large protein complexes on semiconducting substrates. Employing this method, photosystem I is incorporated into solid‐state biophotovoltaic cells.