Molecularly Resolved Protein Electromechanical Properties

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• 作者：Daniel Axford ; Jason J. Davis ; Nan Wang ; Dongxu Wang ; Tiantian Zhang ; Jianwei Zhao ; Ben Peters
• 刊名：Journal of Physical Chemistry B
• 出版年：2007
• 出版时间：August 2, 2007
• 年：2007
• 卷：111
• 期：30
• 页码：9062 - 9068
• 全文大小：325K
• 年卷期：v.111,no.30(August 2, 2007)
• ISSN：1520-5207

文摘

Previous work has shown that protein molecules can be trapped between the conductive surfaces presentedby a metal-coated AFM probe and an underlying planar substrate where their molecule-specific conductancecharacteristics can be assayed. Herein, we demonstrate that transport across such a derived metal-protein-electrode junction falls within three, pressure-dependent, regimes and, further, that pressure-dependentconductance can be utilized in analyzing temporal variations of protein fold. Specifically, the electronic andmechanical properties of the metalloprotein azurin have been characterized under conditions of anisotropicvertical compression through the use of a conducting atomic force microscope (CP-AFM). By utilizing theability of azurin to chemically self-assemble on the gold surface presented either by the apex of a suitablycoated AFM probe or a planar metallic surface, molecular-level transport characteristics are assayable. Underconditions of low force, typically less than 2 nN, the weak physical and electronic coupling between theprotein and the conducting contacts impedes tunneling and leads to charge buildup followed by dielectricbreakdown. At slightly increased force, 3-5 nN, the copper protein exhibits temporal electron occupationwith observable negative differential resistance, while the redox-inactive zinc mutant does not. At imposedloads greater than 5 nN, appreciable electron tunneling can be detected even at low bias for both the redox-active and -inactive species. Dynamic current-voltage characteristics have been recorded and are well-describedby a modified Simmons tunneling model. Subsequent analyses enable the electron tunneling barrier heightand barrier length to be determined under conditions of quantified vertical stress. The variance observeddescribes, in essence, the protein's mechanical properties within the confines of the tunnel junction.