A team of investigators from the Molecular Foundry announce that atomic force mciroscopy can now be used to determine how a certain class of proteins promotes the development of crystals in cell-like environments.

The work focused on analyzing surface-layer (S-layer) proteins, which are the primary point of contact between Bacteria, extremophiles and other types of microbes, and their environments.

These molecules assemble in such a manner that they create a crystalline envelope around cells, which protect them from attacks, but also act as an interface for the microorganisms.

Using atomic force microscopy (AFM), the researchers who led the new work saw in real time how this special type of proteins assembled into the crystalline structure. The proteins were in a cell-like environment.

The work was carried out at the Foundry, which is a nanoscience user facility at the US Department of Energy's (DOE) Lawrence Berkeley National Laboratory (Berkeley Lab).

According to members of the research group, this investigation is extremely important for a variety of research fields, ranging from physics and chemistry to medicine.

Microbiologists, for example, could use the new data to develop models that could explain how and why certain bacteria and microbes are immune to the actions of antibiotics designed to kill them.

“Many proteins self-assemble into highly ordered structures that provide organisms with critical functions, such as cell adhesion to surfaces, transformation of CO2 into minerals, propagation of disease, and drug resistance,” explains scientist James DeYoreo.

“This work is the first to provide a direct molecular-level view of the assembly pathway in vitro,” adds the expert, who is also the Deputy Director of the Molecular Foundry.

“Once this knowledge can be extended to assembly in a living system, it may lead to strategies for capitalizing on or interfering with these functions,” he goes on to say.

“We can actually see these proteins from solution sticking and arranging on the lipid bilayers where they spontaneously condense into many protein blobs – then, minutes later, they transform into a crystalline structure with a square lattice of tetramers,” adds Sungwook Chung.

He is a staff scientist in the Physical Biosciences Division at Berkeley, and also a user at the Molecular Foundry.

“This is an important discovery as it gives direct evidence for a multi-stage assembly pathway with an intermediate, amorphous phase forming before folding into a two-dimensional, crystalline array,” Chung concludes.

This investigation is covered by two research papers, which appear in the journals Proceedings of the National Academy of Sciences (PNAS) and Physical Review Letters, respectively.




Description: Video showing how S-layer proteins form crystalline structures in a cell-like environment
Credit: Berkeley Lab