Fig 7.

Model for the outer shell structure of β-carboxysomes from Synechococcus elongatus PCC 7942. CcmK2, -K3, and -K4 produce flattened hexamers, and CcmK2 is by far the most abundant form. CcmO is postulated to form flattened trimers that could potentially interface with the triangular facets. The rarer CcmL pentamers would close the 5-fold vertices. The carboxysome model is not drawn to scale. Protein structure images were generated using Jmol (240), based on structures of the following proteins: CcmK (Protein Data Bank [PDB] entry 2A1B) (147), CcmO (represented by the structure of CsoS1D [PDB entry 3F56]) (120), and CcmL (PDB entry 2QW7) (147).