Molecular Logic of Prokaryotic Surface Layer Structures

Most prokaryotic cells are encased in a surface layer (S-layer) consisting of a paracrystalline array of repeating lattice-forming proteins. S-layer proteins populate a vast and diverse sequence space, performing disparate functions in prokaryotic cells, including cellular defense, cell-shape maintenance, and regulation of import and export of materials. This article highlights recent advances in the understanding of S-layer structure and assembly, made possible by rapidly evolving structural and cell biology methods. We underscore shared assembly principles revealed by recent work and discuss a common molecular framework that may be used to understand the structural organization of S-layer proteins across bacteria and archaea. Despite enormous sequence diversity in surface (S)-layer proteins, structural diversity is much lower than previously thought.S-layer proteins have a bipartite arrangement with a lattice-forming and an anchoring segment.Novel structural biology methods are revealing the architectures of S-layers in situ.S-layer assembly across prokaryotes is tightly coupled to the cell cycle, including the cell division machinery.