A multi-scale examination of protein surface layer assembly and function in bacteria and archaea
- Surface layers (S-layers) are nanoporous shells of crystalline protein surrounding a great diversity of bacteria and nearly all known archaea. As the outermost component of the cell envelope, S-layers are one of the most abundant biopolymers on earth and are implicated in functions ranging from providing the structural integrity of the cell to mediating host-pathogen interactions. In this thesis, I report a multi-scale analysis of S-layers from the model bacterium Caulobacter crescentus and a more recently cultivated thaumarchaeote, Nitrosoarchaeum limnia. By first biophysically characterizing the S-layer protein (SLP) from C. crescentus, RsaA, I discovered that environmental calcium mediates multiple physical states of the S-layer. I leveraged this knowledge to reconstitute and specifically image S-layer assembly in living cells. Super-resolution fluorescence microscopy and single-molecule tracking demonstrated that remarkably fast and efficient continuous 2D protein crystallization governs S-layer self-assembly. I further examined the rapid 2D crystallization of RsaA using a combination of time-resolved small angle x-ray scattering (SAXS) and electron cryo-microscopy (Cryo-EM). These observations revealed that a multi-step crystallization pathway involving a short-lived crystalline intermediate is responsible for rapid self-assembly of RsaA. Robust S-layer lattice formation has implications for essential cell functions such as energy production, which in the ammonia-oxidizing archaeaon N. limnia likely occurs within the pseudo-periplasmic space between the cell's only lipid membrane and the extracellular S-layer. Electrodiffusion simulations of the N. limnia cell envelope suggest that the S-layer facilitates diffusion of its main energy source, ammonium ions, through the nanopores of the S-layer by creating a charged protein surface. As such, we propose ion transport as an evolutionary basis for conservation of charged amino acids among archaeal SLPs. Taken together, these findings inform the development of antibiotics mediating S-layer biology and provide insight into possible avenues to design biologically inspired self-assembling macromolecular nanomaterials.
|Type of resource
|electronic resource; remote; computer; online resource
|1 online resource.
|Herrmann, Jonathan Robert
|Degree committee member
|Degree committee member
|Stanford University, Department of Structural Biology.
|Statement of responsibility
|Submitted to the Department of Structural Biology.
|Thesis Ph.D. Stanford University 2019.
- © 2019 by Jonathan Robert Herrmann
- This work is licensed under a Creative Commons Attribution Non Commercial 3.0 Unported license (CC BY-NC).
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