Temperature and force dependence of nanoscale electron transport via the Cu protein azurin

ACS Nano. 2012 Dec 21;6(12):10816-24. doi: 10.1021/nn3041705. Epub 2012 Nov 14.

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.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Alcaligenes faecalis
  • Apoproteins / chemistry
  • Apoproteins / metabolism
  • Azurin / chemistry*
  • Azurin / metabolism*
  • Electron Transport
  • Immobilized Proteins / chemistry
  • Immobilized Proteins / metabolism
  • Microscopy, Atomic Force / methods*
  • Models, Molecular
  • Nanotechnology / methods*
  • Protein Conformation
  • Temperature*

Substances

  • Apoproteins
  • Immobilized Proteins
  • Azurin