Triton X-100 as an effective surfactant for the isolation and purification of photosystem I from Arthrospira platensis.

Surfactants play important roles in the preparation, structural, and functional research of membrane proteins, and solubilizing and isolating membrane protein, while keeping their structural integrity and activity intact is complicated. The commercial n-Dodecyl-ß-D-maltoside (DDM) and Triton X-100 (TX) were used as solubilizers to extract and purify trimeric photosystem I (PSI) complex, an important photosynthetic membrane protein complex attracting broad interests. With an optimized procedure, TX can be used as an effective surfactant to isolate and purify PSI, as a replace of the much more expensive DDM. A mechanism was proposed to interpret the solubilization process at surfactant concentrations lower than the critical solubilization concentration. PSI-TX and PSI-DDM had identical polypeptide bands, pigment compositions, oxygen consumption, and photocurrent activities. This provides an alternative procedure and paves a way for economical and large-scale trimeric PSI preparation.

Conductive Core-Shell Aramid Nanofibrils: Compromising Conductivity with Mechanical Robustness for Organic Wearable Sensing.

One-dimensional organic nanomaterials with a combination of electric conductivity, flexibility, and mechanical robustness are highly in demand in a variety of flexible electronic devices. Herein, conducting polymers were combined with robust Kevlar nanofibrils (aramid nanofibrils, abbreviated as ANFs) via in situ polymerization. Owing to the strong interactions between ANFs and conjugated polymers, the resultant core-shell ANFs showed high electric conductivity in combination with flexibility, robustness, physical stability, and endurance to bending and solvents, in sharp contrast to many inorganic conductive nanomaterials. Due to their responsivity of conductivity to different stimuli (e.g., humidity and strain), their membranes were capable not only of sensing human motions and speech words, but also of showing high sensitivity to variation of environmental humidity. In such a way, these core-shell ANFs may pave the way for combining both conductivity and mechanical properties applicable for diverse wearable devices.

Cell-Free Expression of Unnatural Amino Acid Incorporated Aquaporin SS9 with Improved Separation Performance in Biomimetic Membranes.

Aquaporins (AQPs) are widely applied in biomimetic membranes for water recycling and desalination. In this study, a novel aquaporin was isolated from Photobacterium profundum SS9 (AQP SS9), which showed high water permeability and potential for practical water purification applications. To improve the stability of the AQP SS9 embedded biomimetic membranes, a modified AQP SS9 was obtained by incorporation of an unnatural amino acid (p-propargyloxyphenylalanine, pPpa) (P-AQP SS9) in vitro using a mutated Methanocaldococcus jannaschii tyrosyl-tRNA synthetase (TyrRS) and the cell-free expression system. The modified AQP SS9 can covalently link with phospholipids and hence significantly improve the stability of biomimetic membranes. The concentration of Mg2+ and fusion expression with signal peptides were evaluated to enhance the expression level of P-AQP SS9, resulting in a highest yield of 49 mg/L. The modified AQP SS9 was then reconstituted into DOPC liposomes and analyzed by a stopped-flow spectrophotometer. The obtained water permeability coefficient (Pf) of 7.46×10-4 m/s was 5.7 times higher than that of proteoliposomes with the wild-type AQP SS9 (Pf=1.31×10-4 m/s) and 12.1 times higher than that of the DOPC liposomes (Pf=6.15×10-5m/s). This study demonstrates the development of a cell-free system for the expression of membrane proteins with much higher stability and the potential application of the modified aquaporins for water filtration.

Designer amphiphilic short peptides enhance thermal stability of isolated photosystem-I.

Stability of membrane protein is crucial during protein purification and crystallization as well as in the fabrication of protein-based devices. Several recent studies have examined how various surfactants can stabilize membrane proteins out of their native membrane environment. However, there is still no single surfactant that can be universally employed for all membrane proteins. Because of the lack of knowledge on the interaction between surfactants and membrane proteins, the choice of a surfactant for a specific membrane protein remains purely empirical. Here we report that a group of short amphiphilic peptides improve the thermal stability of the multi-domain protein complex photosystem-I (PS-I) in aqueous solution and that the peptide surfactants have obvious advantages over other commonly used alkyl chain based surfactants. Of all the short peptides studied, Ac-I(5)K(2)-CONH(2) (I(5)K(2)) showed the best stabilizing effect by enhancing the melting temperature of PS-I from 48.0 degrees C to 53.0 degrees C at concentration of 0.65 mM and extending the half life of isolated PS-I significantly. AFM experiments showed that PS-I/I(5)K(2)/Triton X-100 formed large and stable vesicles and thus provide interfacial environment mimicking that of native membranes, which may partly explain why I(5)K(2) enhanced the thermal stability of PS-I. Hydrophobic and hydrophilic group length of I(x)K(y) had an important influence on the stabilization of PS-I. Our results showed that longer hydrophobic group was more effective in stabilizing PS-I. These simple short peptides therefore exhibit significant potential for applications in membrane protein studies.