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bioRxiv · 10.1101/538397

Continuous, Topologically Guided Protein Crystallization Controls Bacterial Surface Layer Self-Assembly

Comerci, C. J.·Herrmann, J.·Yoon, J.·Jabbarpour, F.·Zhou, X.·Nomellini, J. F.·Smit, J.·Shapiro, L.·Wakatsuki, S.·Moerner, W. E.
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Abstract

Bacteria assemble the cell envelope using localized enzymes to account for growth and division of a topologically complicated surface1-3. However, a regulatory pathway has not been identified for assembly and maintenance of the surface layer (S-layer), a 2D crystalline protein coat surrounding the curved 3D surface of a variety of bacteria4,5. By specifically labeling, imaging, and tracking native and purified RsaA, the S-layer protein (SLP) from C. crescentus, we show that protein self-assembly alone is sufficient to assemble and maintain the S-layer in vivo. By monitoring the location of newly produced S-layer on the surface of living bacteria, we find that S-layer assembly occurs independently of the site of RsaA secretion and that localized production of new cell wall surface area alone is insufficient to explain S-layer assembly patterns. When the cell surface is devoid of a pre-existing S-layer, the location of S-layer assembly depends on the nucleation characteristics of SLP crystals, which grow by capturing RsaA molecules freely diffusing on the outer bacterial surface. Based on these observations, we propose a model of S-layer assembly whereby RsaA monomers are secreted randomly and diffuse on the lipopolysaccharide (LPS) outer membrane until incorporated into growing 2D S-layer crystals. The complicated topology of the cell surface enables formation of defects, gaps, and grain boundaries within the S-layer lattice, thereby guiding the location of S-layer assembly without enzymatic assistance. This unsupervised mechanism poses unique challenges and advantages for designing treatments targeting cell surface structures or utilizing S-layers as self-assembling macromolecular nanomaterials. As an evolutionary driver, 2D protein self-assembly rationalizes the exceptional S-layer subunit sequence and species diversity6.

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Comerci, C. J., Herrmann, J., Yoon, J., Jabbarpour, F., Zhou, X., Nomellini, J. F., Smit, J., Shapiro, L., Wakatsuki, S., Moerner, W. E.. 2019-02-01. Continuous, Topologically Guided Protein Crystallization Controls Bacterial Surface Layer Self-Assembly. https://doi.org/10.1101/538397

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