Fig 6.

(A) Comparison of the components and possible RubisCO packing within α- and β-carboxysomes. Note that the latter structures are always bigger than the former (see Fig. 4B). It is likely that the β-carboxysome has an outer layer composed of CcmK, CcmO, and CcmL, while the inner, less-dense, RubisCO-attached layer is composed of CcmM, CcaA, and CcmN; the interior appears to be paracrystalline and possibly organized by the shorter form of CcmM. For comparison, the smaller α-carboxysomes may feature a shell that is composed mostly of CsoS1 and CsoS4 forms, with less organization of internal RubisCO. (B) Comparison of the diameters and volumes of extreme carboxysomes of both types (112, 159, 238, 239). The inset shows the relationship between internal volume and maximum cross-sectional diameter, assuming that this measurement is the same as the diameter of a sphere circumscribing a perfectly icosahedral carboxysome. The volume of each carboxysome type is shown and is indicated by an asterisk on the curve.