  Bacterial microcompartments are large, roughly icosahedral shells that
assemble around enzymes and reactants involved in certain metabolic pathways in
bacteria. Motivated by microcompartment assembly, we use coarse-grained
computational and theoretical modeling to study the factors that control the
size and morphology of a protein shell assembling around hundreds to thousands
of molecules. We perform dynamical simulations of shell assembly in the
presence and absence of cargo over a range of interaction strengths, subunit
and cargo stoichiometries, and the shell spontaneous curvature. Depending on
these parameters, we find that the presence of a cargo can either increase or
decrease the size of a shell relative to its intrinsic spontaneous curvature,
as seen in recent experiments. These features are controlled by a balance of
kinetic and thermodynamic effects, and the shell size is assembly pathway
dependent. We discuss implications of these results for synthetic biology
efforts to target new enzymes to microcompartment interiors.
