title: Electron Transfer Proteins as Electronic Conductors: Significance of the Metal and Its Binding Site in the Blue Cu Protein, Azurin.
abstract: Electron transfer (ET) proteins are biomolecules with specific functions, selected by evolution. As such they are attractive candidates for use in potential bioelectronic devices. The blue copper protein azurin (Az) is one of the most-studied ET proteins. Traditional spectroscopic, electrochemical, and kinetic methods employed for studying ET to/from the protein's Cu ion have been complemented more recently by studies of electrical conduction through a monolayer of Az in the solid-state, sandwiched between electrodes. As the latter type of measurement does not require involvement of a redox process, it also allows monitoring electronic transport (ETp) via redox-inactive Az-derivatives. Here, results of macroscopic ETp via redox-active and -inactive Az derivatives, i.e., Cu(II) and Cu(I)-Az, apo-Az, Co(II)-Az, Ni(II)-Az, and Zn(II)-Az are reported and compared. It is found that earlier reported temperature independence of ETp via Cu(II)-Az (from 20 K until denaturation) is unique, as ETp via all other derivatives is thermally activated at temperatures >≈200 K. Conduction via Cu(I)-Az shows unexpected temperature dependence >≈200 K, with currents decreasing at positive and increasing at negative bias. Taking all the data together we find a clear compensation effect of Az conduction around the Az denaturation temperature. This compensation can be understood by viewing the Az binding site as an electron trap, unless occupied by Cu(II), as in the native protein, with conduction of the native protein setting the upper transport efficiency limit.
authors.affiliation: Departments of Materials and Interfaces Weizmann Institute of Science Rehovot 76100 Israel; Departments of Organic Chemistry Weizmann Institute of Science Rehovot 76100 Israel.
authors.forename: Nadav
authors.initials: N
authors.lastname: Amdursky
authors.affiliation: Departments of Materials and Interfaces Weizmann Institute of Science Rehovot 76100 Israel.
authors.forename: Lior
authors.initials: L
authors.lastname: Sepunaru
authors.affiliation: Departments of Materials and Interfaces Weizmann Institute of Science Rehovot 76100 Israel; Departments of Organic Chemistry Weizmann Institute of Science Rehovot 76100 Israel.
authors.forename: Sara
authors.initials: S
authors.lastname: Raichlin
authors.affiliation: Departments of Immunology Weizmann Institute of Science Rehovot 76100 Israel.
authors.forename: Israel
authors.initials: I
authors.lastname: Pecht
authors.affiliation: Departments of Organic Chemistry Weizmann Institute of Science Rehovot 76100 Israel.
authors.forename: Mordechai
authors.initials: M
authors.lastname: Sheves
authors.affiliation: Departments of Materials and Interfaces Weizmann Institute of Science Rehovot 76100 Israel.
authors.forename: David
authors.initials: D
authors.lastname: Cahen
keywords: compensation effect; electron transport; temperature dependence