Application of Peptide Gemini Surfactants as Novel Solubilization Surfactants for Photosystems I and II of Cyanobacteria

Abstract

We designed novel peptide gemini surfactants (PG-surfactants), DKDKC12K and DKDKC12D, which can solubilize Photosystem I (PSI) of Thermosynecoccus elongatus and Photosystem II (PSII) of Thermosynecoccus vulcanus in an aqueous buffer solution. To assess the detailed effects of PG-surfactants on the original supramolecular membrane protein complexes and functions of PSI and PSII, we applied the surfactant exchange method to the isolated PSI and PSII. Spectroscopic properties, light-induced electron transfer activity, and dynamic light scattering measurements showed that PSI and PSII could be solubilized not only with retention of the original supramolecular protein complexes and functions but also without forming aggregates. Furthermore, measurement of the lifetime of light-induced charge-separation state in PSI revealed that both surfactants, especially DKDKC12D, displayed slight improvement against thermal denaturation below 60 °C compared with that using β-DDM. This degree of improvement in thermal resistance still seems low, implying that the peptide moieties did not interact directly with membrane protein surfaces. By conjugating an electron mediator such as methyl viologen (MV(2+)) to DKDKC12K (denoted MV-DKDKC12K), we obtained derivatives that can trap the generated reductive electrons from the light-irradiated PSI. After immobilization onto an indium tin oxide electrode, a cathodic photocurrent from the electrode to the PSI/MV-DKDKC12K conjugate was observed in response to the interval of light irradiation. These findings indicate that the PG-surfactants DKDKC12K and DKDKC12D provide not only a new class of solubilization surfactants but also insights into designing other derivatives that confer new functions on PSI and PSII.

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

“…The DLS profiles of 0.1 wt% DKDKC12K-PA5, DKDKC12K-PA7, and DKDKC12K-PA18 in phosphate buffer gave a single peak at 13, 25, and 29 nm, respectively, and an apparent increase in micelle diameters was observed with the increase in Mn of the PA unit. These data also support the idea that DKDKC12K units in DKDKC12K-PAn could form micelles similar to those of DKDKC12K [20] even after the introduction of PA units. Joining of DKDKC12KC and PAn-DTA via S-S bond (Scheme 2) was performed according to Scheme 2, and the target conjugates were purified by reverse-phase high-performance liquid chromatography (RP-HPLC, Figures S2-S4).…”

“…For the surfactant part, we chose the PG-surfactant DKDKC 12 KC, in which one Cys residue was added to the N-terminal side of DKDKC 12 K ( Figure S1). Because DKDKC 12 K has a higher molecular weight (MW 1330) than the general low MW solubilization surfactants such as n-octyl-β-Dglucopyranoside (β-OG, MW 292) and n-dodecyl-β-D-maltopyranoside (β-DDM, MW 511), it was tolerant of introducing other functional groups to the N-or C-terminal of the same molecule without losing its original solubilization function for membrane proteins [20,23]. We expected that DKDKC 12 K would also conjugate hydrophilic polymers without losing the original solubilization function.…”

“…Meanwhile, we recently studied Gemini-type peptide surfactants, PG-surfactants [19][20][21][22][23]. The basic molecular scaffold of PG-surfactants consists of three constituents: the linker peptide from to 3-5 residues (X), two alkylamidomethyl-modified Cys residues at both sides of the linker peptide, and the peripheral peptides (Y and Z) at the N-and C-terminal sides of the alkylamidomethyl-modified Cys residues (Figure 1a).…”

“…The basic molecular scaffold of PG-surfactants consists of three constituents: the linker peptide from to 3-5 residues (X), two alkylamidomethyl-modified Cys residues at both sides of the linker peptide, and the peripheral peptides (Y and Z) at the N-and C-terminal sides of the alkylamidomethyl-modified Cys residues (Figure 1a). From a set of screenings on hydrophilic peptide sequences at X, Y, and Z, we found that two PG-surfactants, DKDKC 12 K and DKDKC 12 D, were able to function as solubilization surfactants for membrane proteins [20]. Furthermore, by the tandem connection of the -Cys(C 12 )-Asp-Lys-Asp-Lys-Cys(C 12 )-units in DKDKC 12 K and DKDKC 12 D via flexible (Gly) 4 linkers in one molecule, we succeeded in designing the high molecular weight (MW) solubilization surfactants, Bis-D 3 -DKDKC 12 (MW~3 kDa), Bis-K 3 -DKDKC 12 (MW~3 kDa), and Tris-D 3 -DKDKC 12 (MW 4.3 kDa) [21].…”

Enhanced Photocurrent Generation From a Single‐Mediated Photo‐Bioelectrochemical Cell Using Wild‐Type Anabaena Variabilis Dispersed in Solution

“…In an early development stage of PBEC systems, PSI and PSII isolated from higher plants or cyanobacteria were widely used as conversion units. Many ingenious, sophisticated integrated structures that incorporate PSI and PSII at both anode and cathode have been constructed aiming at enhancing photocurrent .…”