title: Conjugated Cofactor Enables Efficient Temperature-Independent Electronic Transport Across ∼6 nm Long Halorhodopsin.
abstract: We observe temperature-independent electron transport, characteristic of tunneling across a ∼6 nm thick Halorhodopsin (phR) monolayer. phR contains both retinal and a carotenoid, bacterioruberin, as cofactors, in a trimeric protein-chromophore complex. This finding is unusual because for conjugated oligo-imine molecular wires a transition from temperature-independent to -dependent electron transport, ETp, was reported at ∼4 nm wire length. In the ∼6 nm long phR, the ∼4 nm 50-carbon conjugated bacterioruberin is bound parallel to the α-helices of the peptide backbone. This places bacterioruberin's ends proximal to the two electrodes that contact the protein; thus, coupling to these electrodes may facilitate the activation-less current across the contacts. Oxidation of bacterioruberin eliminates its conjugation, causing the ETp to become temperature dependent (>180 K). Remarkably, even elimination of the retinal-protein covalent bond, with the fully conjugated bacterioruberin still present, leads to temperature-dependent ETp (>180 K). These results suggest that ETp via phR is cooperatively affected by both retinal and bacterioruberin cofactors.
authors: Departments of Materials and Interfaces, ‡Organic Chemistry, and §Immunology, Weizmann Institute of Science , Rehovot 76100, Israel.
authors: Sabyasachi
authors: S
authors: Mukhopadhyay
authors: Departments of Materials and Interfaces, ‡Organic Chemistry, and §Immunology, Weizmann Institute of Science , Rehovot 76100, Israel.
authors: Sansa
authors: S
authors: Dutta
authors: Departments of Materials and Interfaces, ‡Organic Chemistry, and §Immunology, Weizmann Institute of Science , Rehovot 76100, Israel.
authors: Israel
authors: I
authors: Pecht
authors: Departments of Materials and Interfaces, ‡Organic Chemistry, and §Immunology, Weizmann Institute of Science , Rehovot 76100, Israel.
authors: Mordechai
authors: M
authors: Sheves
authors: Departments of Materials and Interfaces, ‡Organic Chemistry, and §Immunology, Weizmann Institute of Science , Rehovot 76100, Israel.
authors: David
authors: D
authors: Cahen
mesh_terms: D002338:Carotenoids / Q000737:chemistry*; D004579:Electron Transport; D025602:Halorhodopsins / Q000737:chemistry*; D008958:Models, Molecular; D011487:Protein Conformation; D013696:Temperature
chemical_list: D025602:Halorhodopsins; D002338:Carotenoids