Doping Human Serum Albumin with Retinoate Markedly Enhances Electron Transport Across the Protein

TL;DR

This study demonstrates that doping human serum albumin with retinoate significantly enhances its electron transport capacity, revealing a temperature-dependent mechanism and potential for tuning protein-based electronic functions.

Contribution

It is the first to show that retinoate binding markedly improves electron transport in human serum albumin, with detailed analysis of the mechanism and temperature effects.

Findings

Electron transport increases by over two orders of magnitude with retinoate doping.

Temperature dependence indicates a change in the electron transport mechanism around 190K.

Binding of retinoate reduces activation energy and distance-decay constant.

Abstract

Electrons can migrate via proteins over distances that are considered long for non-conjugated systems. Proteins' nano-scale dimensions and the enormous flexibility of their structures and chemistry makes them fascinating subjects for investigating the mechanism of their electron transport (ETp) capacity. One particular attractive research direction is that of tuning their ETp efficiency by doping them with external small molecules. Here we report that solid-state ETp across human serum albumin (HSA) increases by more than two orders of magnitude upon retinoate (RA) binding to HSA. RA was chosen because optical spectroscopy has provided evidence for the non-covalent binding of at least three RA molecules to HSA and indications for their relative structural positions. The temperature dependence of ETp shows that both the activation energy and the distance-decay constant decrease with increasing RA binding to HSA. Furthermore, the observed transition from temperature-activated ETp above 190K to temperature-independent ETp below this temperature suggests a change in the ETp mechanism with temperature.