Breadcrumbs and Evolution...

Schematic of the sandwich tunnelling electrode structure functionalized with RGD peptide, with a human integrin &alpha_Vβ₃ protein in the junction gap. Courtesy of Nano Futures.

Topics: Biology, Biochemistry, Chemistry, Nanotechnology

When electrochemistry, transient charging and heating effects all failed to explain the fluctuating high conductance detected in a human integrin protein, Stuart Lindsay at Arizona State University and his colleagues considered the possibility that the protein’s electronic properties teetered at a critical point between conducting and insulating states. Further analysis of the results revealed characteristics typical of a quantum critical point. While as yet unconfirmed, it is possible this "Goldilocks zone" may aid the protein’s functions, so that evolutionary advantages would have promoted the prevalence of this statistically unlikely electronic behaviour. On a more pragmatic level, the distinctive electronic signal is clearly identified against noisy backgrounds, and may have applications in single-molecule detection.

"There has long been this breadcrumb trail of evidence that proteins behave unusually electronically," explains Lindsay, director of the Biodesign Center for Single Molecule Biophysics at Arizona State University. "All the experiments you can shoot down because you don’t know the state of the protein or how many proteins you have there – here, for the first time, we trap a single protein in a well defined gap and in a condition in which the protein is native."

Lindsay worked alongside researchers at Arizona State University in the US and Eötvös Loránd University in Hungary to characterize the proteins both using a scanning tunnelling microscope (STM) similar to other groups, as well as with a "fixed-gap device" junction developed in work on DNA sequencing. Characterizing proteins by STM raises several issues because the precise chemistry and geometry of the STM tip are not known, and the native environment of these proteins differs greatly from a vacuum, where the physics is well established. However, Lindsay and his colleagues found that their less error-prone fixed-gap device also gave conductances several orders of magnitude greater than expected, and that they fluctuated.

Unexplained huge protein conductances hint at evolution, Anna Demming, Nanotechweb.org