Required for alpha-carboxysome (Cb) assembly, mediates interaction between RuBisCO and the Cb shell. The protein is probably intrinsically disordered (Probable). The C-terminal repeats act as the encapsulation signal to target proteins to the Cb; they are necessary and sufficient to target both CsoS2 and foreign proteins to the Cb. The N-terminal repeats of this protein bind simultaneously to both subunits of RuBisCO. Probably also interacts with the major shell proteins (CsoS1); that interaction would increase the local concentration of CsoS2 so that it can condense RuBisCO and full carboxysomes can be formed (By similarity). Probably interacts with the carboxysome major shell protein CsoS1 via the N-terminal domain; this complex probably also interacts with RuBisCO. This bacterium makes alpha-type carboxysomes. Has 3 domains; the N-terminal domain has 4 short repeats, the central region has 6 longer repeats (Probable). The C-terminal domain has 2 repeats and a highly conserved C-terminal peptide. The C-repeats serve as the encapsulation signal for the alpha-carboxysome, and are able to target foreign proteins to this organelle (By similarity). Has been suggested to undergo ribosomal frameshifting, as does its ortholog in H.neapolitanus. The exact position of the putative frameshift is not given, but it would probably occur in the sixth M-repeat and remove the C-terminus. Belongs to the CsoS2 family.