Abstract
The role of natural thylakoid membrane housing of Photosystem I (PSI), the transmembrane photosynthetic protein, in its robust photoactivated charge separation with near unity quantum efficiency is not fundamentally understood. To this end, incorporation of suitable protein scaffolds for PSI incorporation is of great scientific and device manufacturing interest. Areas of interest include solid state bioelectronics, and photoelectrochemical devices that require bio-abio interfaces that do not compromise the photoactivity and photostability of PSI. Therefore, the surfactant-induced membrane solubilization of a negatively charged phospholipid (DPhPG) with the motivation of creating biomimetic reconstructs of PSI reconstitution in DPhPG liposomes is studied. Specifically, a simple yet elegant method for incorporation of PSI trimeric complexes into DPhPG bilayer membranes that mimic the natural thylakoid membrane housing of PSI is introduced. The efficacy of this method is demonstrated via absorption and fluorescence spectroscopy measurements as well as direct visualization using atomic force microscopy. This study provides direct evidence that PSI confinements in synthetic lipid scaffolds can be used for tuning the photoexcitation characteristics of PSI. Hence, it paves the way for development of fundamental understanding of microenvironment alterations on photochemical response of light activated membrane proteins.
Highlights
The quest for green energy has sparked considerable interest in Photosystem I (PSI), the photosynthetic protein complex, that is akin to a nano-scale biological photodiode and enables light-activated charge separation to facilitate unidirectional electron flow[1]
This section details our major results for the PSI-proteoliposome formation with the DPhPG/Triton X-100 (TX-100)/PSI system, which can be briefly summarized as follows: (1) Phase diagrams of surfactant induced DPhPG solubilization; (2) Reconstitution of PSI trimers in DPhPG liposomes analyzed with the aid of absorption spectroscopy, fluorescence measurements and atomic force microscopy imaging
Data are collected from two series of Isothermal titration calorimetry (ITC) solubilization experiments starting with two different lipid concentrations (~1 mg ml−1 and 4 mg ml−1) wherein the respectively. The onset of solubilization (Rsat) and Rsol boundaries are as indicated. (Refer to Supplementary Material for complete phase diagram analysis)
Summary
The quest for green energy has sparked considerable interest in Photosystem I (PSI), the photosynthetic protein complex, that is akin to a nano-scale biological photodiode and enables light-activated charge separation (with nearly 100% quantum efficiency) to facilitate unidirectional electron flow[1]. The first step towards the successful fabrication of such bio-hybrid devices call for systematic assembly of oriented and functional PSI onto desired bio-abio interfaces via suitable protein scaffoldings To this end, one must address the obvious question regarding the role of the natural thylakoid membrane housing of PSI trimeric complex in providing the required structural and functional scaffold to the protein. In our continual effort to investigate the optoelectronic behaviors of PSI confined under different bio-abio interfaces, this study presents a fast and elegant approach to achieve high density PSI encapsulation in synthetic lipid bilayer membranes to constitute PSI-proteoliposomes To this end, we have recently investigated the phase transitions during detergent mediated solubilization of negatively charged 1,2-dipalmitoyl-sn-glycero3-phospho-(1′-rac-glycerol) (DPPG) liposomes, a member of the PG lipid family. It should be noted that DPhPC is a branched phosphatidylcholine (PC) lipid with high thermal and structural stability[28]
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