Table 1.

Known structures of shell proteins from bacterial microcompartments.

Protein	Structure	Properties
α-Carboxysome (e.g. Halothiobacillus neapolitanus)
CsoS1A	Single-BMC domain hexamer	Major shell component.
CsoS1C	Single-BMC domain hexamer	Major shell component.
CsoS1D	Tandem-BMC domain (permuted) trimer	Trimers stack to form a hexamer with D3 symmetry; open and closed conformations suggest gated transport.
CsoS4A/B	Pentamer (non-BMC domain)	Minor shell component; believed to form icosahedral vertices.
β-Carboxysome (e.g. Synechocystis PCC6803)
CcmK1	Single-BMC domain hexamer	Major shell component.
CcmK2	Single-BMC domain hexamer	Major shell component.
CcmK4	Single-BMC domain hexamer	Minor shell component.
CcmL	Pentamer (non-BMC domain)	Minor shell component; believed to form icosahedral vertices.
Pdu Microcompartment (e.g. Salmonella enterica)
PduA	Single-BMC domain hexamer	Major shell component.
PduT	Tandem-BMC domain trimer	Pore likely involved in electron transport or Fe-S cluster transport.
PduU	Single-BMC domain hexamer (permuted)	Minor shell component; pore is blocked by 6-stranded β-barrel in crystal structure.
Eut Microcompartment (e.g. S. enterica & E. coli)
EutK	Single-BMC domain fused to helix-turn-helix (HTH) domain	HTH motif with positively charged surface suggests role in nucleic acid binding.
EutL	Tandem-BMC domain trimer	Pore observed in open and closed conformations; probable role in gated transport.
EutM	Single-BMC domain hexamer	Probable major shell component.
EutN	Non-BMC domain hexamer	Crystallizes as a hexamer despite homology to pentameric CcmL/CsoS4 family; role unclear.
EutS	Single-BMC domain (permuted) hexamer	Hexamer forms bent structure with C2 symmetry; possible role in edge formation within shell.
Other Microcompartments
EtuB	Tandem-BMC domain (permuted) trimer	Part of presumptive ethanol utilization microcompartment in Clostridium kluyveri.
PduT homolog	Tandem-BMC domain trimer	Part of microcompartment of uncharacterized function in Desulfitobacterium halfniense.