Visualization of Bacterial Microcompartment Facet Assembly Using High-Speed Atomic Force Microscopy

Bacterial microcompartments (BMCs)
are proteinaceous organelles widespread among bacterial phyla. They
compartmentalize enzymes within a selectively permeable shell and
play important roles in CO2 fixation, pathogenesis, and
microbial ecology. Here, we combine X-ray crystallography and high-speed
atomic force microscopy to characterize, at molecular resolution,
the structure and dynamics of BMC shell facet assembly. Our results
show that preformed hexamers assemble into uniformly oriented shell
layers, a single hexamer thick. We also observe the dynamic process
of shell facet assembly. Shell hexamers can dissociate from and incorporate
into assembled sheets, indicating a flexible intermolecular interaction.
Furthermore, we demonstrate that the self-assembly and dynamics of
shell proteins are governed by specific contacts at the interfaces
of shell proteins. Our study provides novel insights into the formation,
interactions, and dynamics of BMC shell facets, which are essential
for the design and engineering of self-assembled biological nanoreactors
and scaffolds based on BMC architectures.