A Next-Generation qPlus-Sensor-Based AFM Setup: Resolving Archaeal S-Layer Protein Structures in Air and Liquid

Surface-layer (S-layer) proteins form the outermost envelopeinmany bacteria and most archaea and arrange in two-dimensional quasicrystallinestructures via self-assembly. We investigated S-layer proteins extractedfrom the archaeon Pyrobaculum aerophilium with aqPlus sensor-based atomic force microscope (AFM) in both liquid andambient conditions and compared it to transmission electron microscopy(TEM) images under vacuum conditions. For AFM scanning, a next-generationliquid cell and a new protocol for creating long and sharp sapphiretips was introduced. Initial AFM images showed only layers of residualdetergent molecules (sodium dodecyl sulfate, SDS), which are usedto isolate the S-layer proteins from the cells. SDS was not visiblein the TEM images, requiring more thorough sample preparation forAFM measurements. These improvements allowed us to resolve the crystallikestructure of the S-layer samples with frequency-modulation AFM inboth air and liquid.

Automated summary

Researchers compared the S-layer proteins extracted from the archaeon Pyrobaculum aerophilium using atomic force microscopy (AFM) in liquid and ambient conditions with transmission electron microscopy (TEM) images under vacuum conditions. Improved AFM scanning and sample preparation methods allowed the observation of the crystalline structure of the S-layer samples.