A New Class of Purple Membrane Variants for the Construction of Highly Oriented Membrane Assemblies on the Basis of Noncovalent Interactions

Abstract

Purple membranes (PM) from Halobacterium salinarum have been discussed for several technical applications. These ideas started just several years after its discovery. The biological function of bacteriorhodopsin (BR), the only protein in PM, is the light-driven proton translocation across the membrane thereby converting light energy into chemical energy. The astonishing physicochemical robustness of this molecular assembly and the ease of its isolation triggered ideas for technical uses. All basic molecular functions of BR, that is, photochromism, photoelectrism, and proton pumping, are key elements for technical applications like optical data processing and data storage, ultrafast light detection and processing, and direct utilization of sunlight in adenosine 5'-triphospate (ATP) generation or seawater desalination. In spite of the efforts of several research groups worldwide, which confirmed the proof-of-principle for all these potential applications, only the photochromism-based applications have reached a technical level. The physical reason for this is that no fixation or orientation of the PMs is required. The situation is quite different for photoelectrism and proton pumping where the macroscopic orientation of PMs is a prerequisite. For proton pumping, in addition, the formation of artificial membranes which prevent passive proton leakage is necessary. In this manuscript, we describe a new class of PM variants with oppositely charged membrane sides which enable an almost 100% orientation on a surface, which is the key element for photoelectric applications of BR. As an example, the mutated BR, BR-E234R7, was prepared and analyzed. A nearly 100% self-orientation on mica was obtained.

Nanoscale Electric Characteristics and Oriented Assembly of Halobacterium salinarum Membrane Revealed by Electric Force Microscopy

“…The membrane is clearly detected by displaying the two surface potential levels of 0 mV and −9 mV relative to the silicon substrate, which reflects the potential difference between the CP side and the EC side of PM. It is known that the potential of the CP side of PM is 8–10 mV higher than that of the EC side [23,36]. Therefore, dark blue patches can be attributed to the EC side facing upward and the lower contrast patches can be attributed to the CP side facing upward.…”

“…Numerous applications can be employed based on its energy conversion and photoelectrism properties [40,41]. Several different approaches have been explored and applied for directional PM assembly in device configurations in the past with varying degrees of success, such as chemical assembly [42], electric field sedimentation [43], and BR mutation [36]. In order to directionally assemble PM on solid substrate and make functional devices, de novo peptides were employed to modify the substrate.…”

Photonic Structures in Biology: A Possible Blueprint for Nanotechnology

“…[71][72][73] While the exact mechanism of cubic membrane formation is still not fully resolved, recent studies have identified several key components, such as conical phospholipids, 74,75 cholesterol molecules 76 and membrane proteins. 71,[77][78][79][80][81] Conical lipids have packing parameters greater than one and induce negative curvature within the lipid bilayer. The lipid's head and splayed chains form a wedge in the bilayer, 82 facilitating the formation of gyroid and diamond-structured lattices.…”

Preliminary Ultrasonication Affects the Rate of the Bacteriorhodopsin Bleaching and the Effectiveness of the Reconstitution Process in Bacterioopsin

“…Bacteriorhodopsin belongs to the class of biological reversible photosensitive media. It has been widely investigated for use in many technological applications such as real‐time holography , erasable optical storage , light modulation , etc. The optical properties of BR, which define the possible applications, can be modified by changing its environment (matrix, chemical additives, temperature, etc.…”