Engineering Bacterial S-Layer Protein Arrays to Generate Hybrid Nanomaterials

Biological systems have exploited protein self-assembly to evolve hierarchically complex materials with a rich structural and functional palette. The generation of existing hard-soft composites is currently limited by the inability to create precise, tunable patterns at multiple length scales, thus restricting the dimensionality and complexity of patterning for these materials.

Here, we employ protein engineering approaches to modify 2D self-organising proteins to develop protein surfaces for the simultaneous and controlled deposition of multiple types of nanoparticles. We have taken advantage of the intricate self-assembly pathway of surface-layer (S-layer) proteins, specifically SbsB from thermostable Geobacillus stearothermophilus, to construct molecularly diverse, highly-ordered nanostructures. These proteins, localized on the outer cell wall of bacteria and archaea, organize into two-dimensional crystalline arrays and serve as exceptional organic nanoscaffolds.

We utilise a variety of embellishment methods, including modification of unstructured C-terminal sequences, peptide and thiol chemistry, to selective pattern the S-layer surface with mixtures of metal, ceramic and upconverting nanoparticles. Additionally, we show that covalent fusion of SbsB monomers can successfully yield S-layer polyproteins. Upon self-assembly, these modified nanosheets will encompass custom unit cell dimensions and lattice features, diversifying the spatial and binding capabilities of this two-dimensional material. Thus, these methodologies allow us to fabricate novel biocomposites that extend the potential of hybrid hard-soft materials.