Altering the mechanical properties of self-assembled filaments through engineering of EspA bacterial protein

Protein-based biomaterials are in high demand due to their high biocompatibility, non-toxicity, and biodegradability. In this study, we explore the bacterial <i>E. coli</i> secreted protein A (EspA), which self-assembles into long extracellular filaments, as a potential building block for new protein-based biomaterials. We investigated the morphological and mechanical properties of EspA filaments and how protein engineering can modify them. Our study include three types of filaments: natural EspA filaments, full-length recombinant EspA filaments, and truncated recombinant EspA filaments lacking a third of the original codon region. The recombinant EspA proteins formed curly, thin filaments with higher longitudinal elasticity (shorter persistence length) compared to the natural, linear filaments. Additionally, the recombinant filaments had a radial elastic modulus about an order of magnitude lower than the natural filaments. The truncated recombinant filaments had a higher radial modulus than the full-length ones, and unlike the purely elastic natural filaments, recombinant filaments were less compliant with the applied force that penetrated them. These differences underscore the potential to modulate EspA filament properties through protein sequence mutations. Our findings suggest EspA as a fundamental element for developing a new biomaterial with a hierarchical structure, enabling the fabrication of macroscopic substances from self-assembled EspA-modulated filaments.