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1.S.2.  The Bacterial Microcompartment Shell/Pore-forming Protein-2 (BMC-SP2) Family 

In contrast to the BMC-SP1 family which consists of small proteins of about 100 aas, the BMC-SP2 family consists of proteins of somewhat greater than 200 aas and are non-homologous to the BMC-SP1 proteins. However, they contribute to shell formation, sometimes in the same BMC shell as a BMC-SP1 protein as in the ethanolamine utilizing (Eut) BMC of E. coli, and both types of shell proteins form pores (Takenoya et al. 2010).  In contrast to EutL (BMC-SP1), the pore of EutM (BMC-SP2) appears to be positively carged, indicating specificity for different solutes.  Moreover, only the pore of EutL can be triggered to open by exposure to zinc ions (Takenoya et al. 2010).

References associated with 1.S.2 family:

Takenoya, M., K. Nikolakakis, and M. Sagermann. (2010). Crystallographic insights into the pore structures and mechanisms of the EutL and EutM shell proteins of the ethanolamine-utilizing microcompartment of Escherichia coli. J. Bacteriol. 192: 6056-6063. 20851901