Abstract
Bacterial microcompartments, BMCs, are organelles that
exist within wide variety of bacteria and act as nanofactories. Among the
different types of known BMCs, the carboxysome has been studied the
most. The carboxysome plays an important role in the light-independent
part of the photosynthesis process, where its icosahedral-like proteina-
ceous shell acts as a membrane that controls the transport of metabolites.
Although a structural model exists for the carboxysome shell, it remains
largely unknown how the shell proteins self-assemble. Understanding the
self-assembly process can provide insights into how the shell affects the
carboxysome’s function and how it can be modified to create new
functionalities, such as artificial nanoreactors and artificial protein
membranes. Here, we describe a theoretical framework that employs
Monte Carlo simulations with a coarse-grain potential that reproduces
well the atomistic potential of mean force; employing this framework, we
are able to capture the initial stages of the 2D self-assembly of CcmK2 hexamers, a major protein-shell component of the carboxysome’s facet. The simulations reveal that CcmK2 hexamers self-assemble into clusters that resemble what was seen experimentally in 2D layers. Further analysis of the simulation results suggests that the 2D self-assembly of carboxysome’s facets is driven by a nucleation−growth process, which in turn could play an important role in the hierarchical self- assembly of BMC shells in general.
