Electron Transfer Proteins as Electronic Conductors: Significance of the Metal and Its Binding Site in the Blue Cu Protein, Azurin. Issue 4 (16th March 2015)

• Record Type: Journal Article
• Authors: Amdursky, Nadav; Sepunaru, Lior; Raichlin, Sara; Pecht, Israel; Sheves, Mordechai; Cahen, David
• Is Part Of: Advanced science. Volume 2:Issue 4(2015:Apr.)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2015-03-16
• Subjects: compensation effect -- electron transport -- temperature dependence; Science -- Periodicals; 505
• DOI: 10.1002/advs.201400026
• Languages: English
• ISSNs: 2198-3844

Abstract

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. Abstract : Electronic conduction via proteins is of fundamental and practical interest. Using azurin and its derivatives, the para meters that dictate conduction efficiency are investigated. The temperature dependence of conduction hints at a role of the protein's secondary structure, as it fits the Meyer–Neldel rule with the compensation temperature at denaturation.