De novo rational design of a freestanding, supercharged polypeptide, proton-conducting membrane

Abstract

Proton translocation enables important processes in nature and man-made technologies. However, controlling proton conduction and fabrication of devices exploiting biomaterials remains a challenge. Even more difficult is the design of protein-based bulk materials without any functional starting scaffold for further optimization. Here, we show the rational design of proton-conducting, protein materials exceeding reported proteinaceous systems. The carboxylic acid–rich structures were evolved step by step by exploring various sequences from intrinsically disordered coils over supercharged nanobarrels to hierarchically spider β sheet containing protein-supercharged polypeptide chimeras. The latter material is characterized by interconnected β sheet nanodomains decorated on their surface by carboxylic acid groups, forming self-supportive membranes and allowing for proton conduction in the hydrated state. The membranes showed an extraordinary proton conductivity of 18.5 ± 5 mS/cm at RH = 90%, one magnitude higher than other protein devices. This design paradigm offers great potential for bioprotonic device fabrication interfacing artificial and biological systems.

The role of the protein–water interface in dictating proton conduction across protein-based biopolymers

“…Until this point, we have established in our study here that the surface of the BSA fiber, formed in the electrospinning process, is important for mediating protons across our polymers. As mentioned in our introduction, several other proteins have shown proton mediating capabilities, 5,7,9 however, all of these works have used a drop-cast version of the proteins, meaning lacking a microstructure such as in our electrospun fibers. Accordingly, the last section of our study will serve as a control of comparing our results obtained with the BSA electrospun fibers to that obtained with a drop-cast BSA film (Fig.…”

“…Inspired by nature, several recent works have utilized proteins for the formation of proton conducting materials. [5][6][7][8][9] Such bioinspired polymeric conductive materials are gaining momentum toward their integration in biomedical applications. 10,11 In addition to their applicative route, much effort was targeted toward deciphering how protons are being transported along such protein-based materials.…”

“…6 The role of charged amino acids has also been proven to be essential in supporting very high proton conductivity across protein-based polymers. 5,9 Another example is the bovine serum albumin (BSA) protein that has been manipulated (by denaturing the protein) through the electrospinning process to receive a free-standing material with a fibrillar structure. 14 The main difference between the use of BSA and all the previously reported protein-/peptide-based materials is the sustainable nature of the BSA protein.…”

Recent Progress Using De Novo Design to Study Protein Structure, Design and Binding Interactions

“…In 2020 Ma et al designed a proton conducting transmembrane protein that exceeded previous proteinaceous systems [ 55 ]. The group began with substituting glutamic acid (Glu or E) residues in the X site of the elastin-like repeat GVGXG n .…”

Light-Modulated Cationic and Anionic Transport Across Protein Biopolymers

“…Accordingly, in recent years we witness the emergent use of proteins as the building blocks for the formation of ionic conducting polymers. [25][26][27][28][29][30][31][32] Importantly, in one of the protein-based systems that were studied, using reflectin films, there was an attempt to use the HPTS photoacid to light-modulate the protonic conductivity, [11] however the observed magnitude of the response was rather low, of only a few percentages. We speculate that it was due to the mixing of the photoacid in low concentration into the film and not covalently attach it to the surface of the protein, especially as it is known that the protein surface has a fundamental role in dictating protonic transport.…”