Features comparison between T4P-like structure obtained by cryo-EC, remote homology detection, and subtomogram averaging. The main dimensions of the T4P-like complex obtained by 3D cryo-EC (Center Left; EMD-14097), remote homology detection (Center), and subtomogram averaging (Center Right; EMD-14096) are compared. The Left and Right boxes show comparable images of the slice through at equivalent levels, from Top to Bottom, for the T4P-like complex obtained by cryo-EC (left box) and by cryo-ET subtomogram averaging (right box), both computed imposing a p6 symmetry. The dark-yellow boxes indicate the noncrystalline regions that are missing in the model obtained by cryo-EC with respect to the model obtained by subtomogram averaging. The S-layer (SL), the outer membrane (OM), and the inner membrane (IM) thicknesses are indicated. Scale bars indicate 50 Å.
Dario Piano Research Group
The cell envelope of the extremophile bacterium Deinococcus radiodurans was studied by cryo-electron microscopy and described with unprecedented detail. In this bacterium, the outermost cell envelope layer, named surface layer, is characterized by a highly regular tiling of proteins extending their crystalline organization to the cell envelope layers below (until the inner membrane). The study shows three main protein complexes, with masses in the MDa range, regularly organized into an astonishing geometrical regularity. The observed organization contributes to protecting the cell against environmental stressors and maintaining an efficient permeation of environmental solutes.
Surface layers (S-layers) are highly ordered coats of proteins localized on the cell surface of many bacterial species. In these structures, one or more proteins form elementary units that self-assemble into a crystalline monolayer tiling the entire cell surface. Here, the cell envelope of the radiation-resistant bacterium Deinococcus radiodurans was studied by cryo-electron microscopy, finding the crystalline regularity of the S-layer extended into the layers below (outer membrane, periplasm, and inner membrane). The cell envelope appears to be highly packed and resulting from a three-dimensional crystalline distribution of protein complexes organized in close continuity yet allowing a certain degree of free space. The presented results suggest how S-layers, at least in some species, are mesoscale assemblies behaving as structural and functional scaffolds essential for the entire cell envelope.
Farci, D., Haniewicz, P., and Piano, D.: The structured organization of Deinococcus radiodurans’ cell envelope, PNAS (2022) e112101, https://doi.org/10.1073/pnas.2209111119