1.S.2.1.3
Trimeric bacterial microcompartment shell protein of 230 aas.  The protein hydropathy plot shows 5 peaks moderate hydrophobicity that may be TMSs.  Two bacterial microcompartment shell proteins [EtuA (ethanol utilization shell protein A) and EtuB] are encoded in the genome clustered with the genes for ethanol utilization. The function of the bacterial microcompartment is to facilitate fermentation by sequestering the enzymes, substrates and intermediates. Recent structural studies of bacterial microcompartment proteins have revealed both hexamers and pentamers that assemble to generate the pseudo-icosahedral bacterial microcompartment shell. Some of these shell proteins have pores on their symmetry axes. Heldt et al. 2009 reported the structure of the trimeric bacterial microcompartment protein EtuB, which has a tandem structural repeat within the subunit and pseudo-hexagonal symmetry. The pores in the EtuB trimer are within the subunits rather than between symmetry related subunits. The evolutionary advantage of this is that it releases the pore from the rotational symmetry constraint allowing more precise control of the fluxes of asymmetric molecules, such as ethanol, across the pore. EtuA was modeled suggesting that the two proteins have the potential to interact to generate the casing for a metabolosome (Heldt et al. 2009).