A component of the bacterial microcompartment (BMC) shell dedicated to ethanolamine degradation. May be involved in cofactor diffusion across the BMC (Probable). Cobalamin is covalently bound to 1 subunit of the trimer on the concave (lumenal) face in a closed pore conformation; whether this is physiologically relevant is unclear (PubMed:25484204). The closed form has 3 very narrow channels (1.3 Angstrom at their narrowest) per trimer lined by acidic and aromatic residues; 2 ethanolamine molecules can bind in each channel, on either side of the constriction. Does not bind acetate, ethanol or acetyl phosphate, all of which are small molecules involved in ethanolamine metabolism (PubMed:25752492). Ethanolamine-binding has been hypothesized to stabilize the EutL central pore in a closed (non-transporting) state. An open pore is thought to be large enough to transport ATP and/or cobalamin (Probable). Homotrimerizes to form a pseudohexamer. Has 2 BMC domains which can evolve independently of each other (Probable). Two ethanolamine molecules bind in the interface between these 2 domains. Ethanolamine 1 binds on the cytoplasmic side, while ethanolamine 2 binds on the lumenal side of the BMC (PubMed:25752492). A disulfide bond is seen in native crystals; it disappears upon reduction with tris-(2-carboxyethyl) phosphine, which also reduces the protein's affinity for ethanolamine. It has been suggested to confer redox modulation to pore opening. Belongs to the EutL/PduB family.