title: Temperature and force dependence of nanoscale electron transport via the Cu protein azurin.
abstract: Solid-state electron transport (ETp) via a monolayer of immobilized azurin (Az) was examined by conducting probe atomic force microscopy (CP-AFM), as a function of both temperature (248-373K) and applied tip force (6-15 nN). At low forces, ETp via holo-Az (with Cu(2+)) is temperature-independent, but thermally activated via the Cu-depleted form of Az, apo-Az. While this observation agrees with those of macroscopic-scale measurements, we find that for holo-Az the mechanism of ETp at high temperatures changes upon an increase in the force applied by the tip to the proteins; namely, above 310 K and forces >6 nN ETp becomes thermally activated. This is in contrast to apo-Az, where increasing applied force causes only small monotonic increases in currents due to decreased electrode separation. The distinct ETp temperature dependence of holo- and apo-Az is assigned to a difference in structural response to pressure between the two protein forms. An important implication of these CP-AFM results (of measurements over a significant temperature range) is that for reliable ETp measurements on flexible macromolecules, such as proteins, the pressure applied during the measurements should be controlled or at least monitored.
authors.affiliation: Department of Materials & Interfaces, Weizmann Institute of Science, Rehovot 76100, Israel.
authors.forename: Wenjie
authors.initials: W
authors.lastname: Li
authors.forename: Lior
authors.initials: L
authors.lastname: Sepunaru
authors.forename: Nadav
authors.initials: N
authors.lastname: Amdursky
authors.forename: Sidney R
authors.initials: SR
authors.lastname: Cohen
authors.forename: Israel
authors.initials: I
authors.lastname: Pecht
authors.forename: Mordechai
authors.initials: M
authors.lastname: Sheves
authors.forename: David
authors.initials: D
authors.lastname: Cahen
mesh_terms: D042481:Alcaligenes faecalis; D001059:Apoproteins / Q000737:chemistry / Q000378:metabolism; D001400:Azurin / Q000737:chemistry* / Q000378:metabolism*; D004579:Electron Transport; D055767:Immobilized Proteins / Q000737:chemistry / Q000378:metabolism; D018625:Microscopy, Atomic Force / Q000379:methods*; D008958:Models, Molecular; D036103:Nanotechnology / Q000379:methods*; D011487:Protein Conformation; D013696:Temperature
chemical_list: D001059:Apoproteins; D055767:Immobilized Proteins; D001400:Azurin