Application of peptide gemini surfactants as novel solubilization surfactants for photosystems I and II of cyanobacteria

Design of stimuli-responsive minimalist heptad surfactants for stable emulsions

Peptide surfactants have been extensively investigated with various applications in detergents, foods, and pharmaceutics due to their biodegradability, biocompatibility, and customizable structures. Traditional peptide surfactants are often designed in a head-to-tail fashion mimicking chemical surfactants. Alternatively, a side-by-side design pattern based on heptad repeats offers an approach to designing peptide surfactants. However, minimalist peptide design using a single heptad for stabilizing interfaces remains largely unexplored. Here, we design four heptad surfactants (AM1.2, 6H, 6H7K, and HK) responsive to metal ions and compare their emulsification performance with a three-heptad peptide, AM1. Among them, the HK peptide generates emulsions exhibiting good stability over months. We further optimize factors such as buffering salts, ionic strength, and emulsion dilutions to uncover their impacts on emulsion properties. Our findings deepen the understanding of emulsion properties and provide practical insights for characterizing peptide-based emulsions, paving the way for their broader utilization in diverse applications.

Solar Energy Conversion through Thylakoid Membranes Wired by Osmium Redox Polymer and Indium Tin Oxide Nanoparticles

For several decades, much attention has been paid to thylakoid membranes (TMs) as photocatalysts for converting solar light to electricity. Despite extensive research, current technology provides only limited photocurrents. Here, a novel method based on TM-composite material was developed for achieving high photocurrent. When a thin film composed of TMs, osmium redox polymer (Os-RP), and indium tin oxide nanoparticles (ITOnp) was formed on a porous graphite surface, appreciable photocurrent as high as 0.5 mA cm^-2 was achieved at 0.4 V vs. Ag/AgCl. Each component plays its own role in transferring electrons from TMs to the anode, resulting in sharp drop in photocurrent with missing any component. Optimization between these three components showed 1 : 0.5 : 30 (TM/Os-RP/ITOnp) was the best ratio. Action spectra confirmed that TMs was the origin of photocurrent. It was inferred from blocking experiments using 3-(3,4-dichlorophenyl)-1,1-dimethylurea as an inhibitor that about 41 % of photocurrent was transferred from Q_A in photosystem II to the electrode via Os-RP and ITOnp. Quantum efficiencies at 430 and 660 nm were 12.2 and 18.5 %, respectively. Turnover frequency for water oxidation depended upon the amount of the composite. A complete cell with Pt/C cathode produced P_max of 122 μW cm^-2 at 758 μA cm^-2 under one sun illumination, which is the highest power density to our knowledge. This study opened a possibility of using TMs as photocatalysts for solar energy conversion.

Facile design of gemini surfactant-like peptide for hydrophobic drug delivery and antimicrobial activity

Recently, many kinds of gemini-type amphiphilic peptides have been designed and shown their advantage as self-assembling nanomaterials. In this study, we proposed a simple strategy to design gemini surfactant-like peptides, which are only composed of natural amino acids and can be easily obtained by conventional peptide sythnesis. Taking two prolines as the turn-forming units, a peptide named APK was designed. The petide has a linear sequence but naturally takes the conformation like a gemini surfactant. Compared with a single-tailed surfactant-like peptide A6K, APK showed much stronger ability to undergo self-assembly and to encapsulate hydrophobic pyrene. Several hydrophobic drugs including paclitaxel, doxorubicin, etomidate and propofol were encapsulated by APK, and the corresponding formulations showed anti-tumor or anesthetic efficacy comparable to their respective clinical formulations. Furthermore, APK could inhibit the growth of different microorganisms including E. coli, S. aureus and C. albicans. Etomidate and propofol formulations encapsulated by APK also showed strong antimicrobial activity. Taking APK as an example, our study indicated a straightforward strategy to design gemini surfactant-like peptides, which could be potential nanomaterials for exploring hydrophobic drug formulations with efficacy, safety and self-antimicrobial activity.

Design of PG-Surfactants Bearing Polyacrylamide Polymer Chain to Solubilize Membrane Proteins in a Surfactant-Free Buffer

The development of techniques capable of using membrane proteins in a surfactant-free aqueous buffer is an attractive research area, and it should be elucidated for various membrane protein studies. To this end, we examined a method using new solubilization surfactants that do not detach from membrane protein surfaces once bound. The designed solubilization surfactants, DKDKC₁₂K-PA_n (n = 5, 7, and 18), consist of two parts: one is the lipopeptide-based solubilization surfactant part, DKDKC₁₂K, fand the other is the covalently connected linear polyacrylamide (PA) chain with different M_w values of 5, 7, or 18 kDa. Intermolecular interactions between the PA chains in DKDKC₁₂K-PA_n concentrated on the surfaces of membrane proteins via amphiphilic binding of the DKDKC₁₂K part to the integral membrane domain was observed. Therefore, DKDKC₁₂K-PA_n (n = 5, 7, and 18) could maintain a bound state even after removal of the unbound by ultrafiltration or gel-filtration chromatography. We used photosystem I (PSI) from Thermosynecoccus vulcanus as a representative to assess the impacts of new surfactants on the solubilized membrane protein structure and functions. Based on the maintenance of unique photophysical properties of PSI, we evaluated the ability of DKDKC₁₂K-PA_n (n = 5, 7, and 18) as a new solubilization surfactant.

Design of New Extraction Surfactants for Membrane Proteins from Peptide Gemini Surfactants

The development of additional extraction surfactants for membrane proteins is necessary for membrane protein research, since optimal combinations for the successful extraction of target membrane proteins from biological membranes that minimize protein denaturation are hard to predict. In particular, those that have a unique basal molecular framework are quite attractive and highly desired in this research field. In this study, we successfully constructed a new extraction surfactant for membrane proteins, NPDGC₁₂KK, from the peptide-gemini-surfactant (PG-surfactant) molecular framework. The PG-surfactant is a U-shaped lipopeptide scaffold, consisting of a short linker peptide (-X-) between two long alkyl-chain-modified Cys residues and a peripheral peptide (Y-) at the N-terminal side of long alkyl-chain-modified Cys residues. Using photosystem I (PSI) and photosystem II (PSII) derived from Thermosynecoccus vulcanus as representative membrane proteins, we evaluated whether NPDGC₁₂KK could solubilize membrane proteins while maintaining structure and functions. Neither the membrane integral domain nor the cytoplasmic domain of PSI and PSII suffered any damage upon the use of NPDGC₁₂KK based on detailed photophysical measurements. Using thylakoid membranes of T. vulcanus as a representative biological membrane sample, we performed experiments to extract membrane proteins, such as PSI and PSII. Based on the extraction efficiency and maintenance of protein supramolecular structure established using clear native-PAGE analyses, we proved that NPDGC₁₂KK functions as a novel class of peptide-containing extraction surfactants for membrane proteins.

Novel gemini cationic lipids with carbamate groups for gene delivery

To obtain efficient non-viral vectors, a series of Gemini cationic lipids with carbamate linkers between headgroups and hydrophobic tails were synthesized. They have the hydrocarbon chains of 12, 14, 16 and 18 carbon atoms as tails, designated as G12, G14, G16 and G18, respectively. These Gemini cationic lipids were prepared into cationic liposomes for the study of the physicochemical properties and gene delivery. The DNA-bonding ability of these Gemini cationic liposomes was much better than their mono-head counterparts (designated as M12, M14, M16 and M18, respectively). In the same series of liposomes, bonding ability declined with an increase in tail length. They were tested for their gene-transferring capabilities in Hep-2 and A549 cells. They showed higher transfection efficiency than their mono-head counterparts and were comparable or superior in transfection efficiency and cytotoxicity to the commercial liposomes, DOTAP and Lipofectamine 2000. Our results convincingly demonstrate that the gene-transferring capabilities of these cationic lipids depended on hydrocarbon chain length. Gene transfection efficiency was maximal at a chain length of 14, as G14 can silence about 80 % of luciferase in A549 cells. Cell uptake results indicate that Gemini lipid delivery systems could be internalised by cells very efficiently. Thus, the Gemini cationic lipids could be used as synthetic non-viral gene delivery carriers for further study.