Photoreceptors for a light biotransducer: a comparative study of the electrical responses of two (type-1)-opsins

TL;DR

This study compares the electrical responses of bacteriorhodopsin and proteorhodopsin, two light-activated proteins, using an impedance network model to understand their potential in bio-photocell applications.

Contribution

It introduces a microscopic impedance network model linking protein structure to electrical responses, providing insights into their semiconducting behavior.

Findings

Proteorhodopsin and bacteriorhodopsin behave like wide gap semiconductors.

The model predicts small-signal Nyquist plots for the proteins.

Intrinsic conductivities are around 10^{-7} S/cm.

Abstract

The increasing interest in photoactivated proteins as natural replacement of standard inorganic materials in photocells drives to the compared analysis of bacteriorhodopsin and proteorhodopsin, two widely diffused proteins belonging to the family of \textit{type-1} opsins. These proteins share similar behaviours but exhibit relevant differences in the sequential chain of the amino acids constituting their tertiary structure. The use of an impedance network analogue to model the protein main features provides a microscopic interpretation of a set of experiments on their photoconductance properties. In particular, this model links the protein electrical responses to the tertiary structure and to the interactions among neighbouring amino acids. The same model is also used to predict the small-signal response in terms of the Nyquist plot. Interesting enough, these rhodopsins are found to behave like a wide gap semiconductor with intrinsic conductivities of the order of $10^{-7}$ S/cm.