Entrapment of Photosystem I within Self-Assembled Films

Abstract

We have developed a process to incorporate an integral membrane protein, Photosystem I (PSI), into an organic thin film at an electrode surface and thereby insulate the protein complex on the surface while mimicking its natural environment. The PSI complex, which is primarily more hydrophobic on the exterior than interior, is hydrophobically confined in vivo within the thylakoid membrane. To mimic the thylakoid membrane and entrap PSI on an electrode, we have designed a series of steps using a thin self-assembled monolayer (SAM) to adsorb and orient PSI followed by exposures to longer-chained methyl-terminated alkanethiols that place exchange with components of the original SAM in the interprotein domains. In this process, PSI is first adsorbed onto a HOC(6)S/Au substrate through a short exposure to a dilute solution of the protein to achieve a protein coverage of approximately 25%. The PSI/HOC(6)S/Au substrate is then placed into a solution containing one of various longer-chained alkanethiols including C(22)SH or C(18)OC(19)SH. Changes in thickness, interfacial capacitance, infrared spectra, and surface wettability were used to assess the extent of backfilling by the long-chained thiols. The coverage of the protein layer and the solvent used for backfilling affected the rate and quality of the SAM formed in the interprotein regions. After exposure of the PSI layer to solvents containing alkanethiols, there was only minor loss of protein on the surface and no real change in protein secondary structure as evidenced by reflectance absorption infrared spectroscopy.

Enhanced Photocurrent Production by Photosystem I Multilayer Assemblies

“…The photocatalytic functionality of this vastly abundant and widely accessible protein has found utility in processes other than photosynthesis, such as bio‐hybrid systems that use light‐energy to produce hydrogen,6–9 as well as photoelectrochemical10–16 and photovoltaic17–22 systems that generate light‐induced increases in electrical currents and voltages. Many of these initial studies investigated the functionality of monolayers of PSI complexes assembled onto various substrates 12, 16, 17, 19, 22–25. Additional work by our group11 and others14 has shown how photocurrents produced by PSI monolayers in electrochemical systems may be enhanced by decorating nanostructured electrodes with PSI because the increased surface area of the substrates could accommodate more PSI complexes than a planar surface of similar geometric area.…”

Detergent–protein interactions in aqueous buffer suspensions of Photosystem I (PS I)

“…To this end, our recent studies have revealed that protein concentrations and driving forces play a significant role in altering the morphological assembly of PS I on SAM substrates when adsorbed from aqueous buffer solutions using gravity driven or electric field assisted directed deposition [4]. Commonly used self-assembly of PS I from buffer solutions onto hydroxyl-terminated alkanethiolate SAM/Au surfaces [3,[32][33][34][35] and a few directed attachment of PS I to Au substrates using platinization techniques [36] have analyzed the attachment dynamics based on surface characterizations using microscopy (AFM) or spectroscopic techniques. Yet, our recent dynamic light scattering (DLS) data have demonstrated that the complex surface morphologies observed in most of these studies mainly arise due to protein-protein interactions in the solution phase [4].…”

Photoelectrochemical cells based on photosynthetic systems: a review

“…With help of the tag, the construction was immobilized on a gold electrode containing self-assembling layer of alkanethiols with a head part as Ni-NTA. It was shown experimentally that the proximity of RCs to the electrode is important for the cell effective operation (Kincaid et al, 2006).…”

“…Many techniques were used for immobilization of photosynthetic complexes, including in particular, bioelectrocatalystic self-assembling monolayers (bio-SAMs) (Nakamura et al, 2000;Kincaid et al, 2006;Frolov, et al, 2008;Mershin et al, 2012); Ni-NTA was attached to polyhistidine tagged PS1 complexes (Fig. 4d) (Das, 2004;Sekar et al, 2014); the redox-active hydrogels (Badura et al, 2008); and fixation on CNTs by means of molecular binding reagents .…”