1,2-propanediol utilization protein U (PduU)/ethanolamine utilization protein S (EutS), Bacterial Micro-Compartment (BMC) domain
PduU encapsulates several related enzymes within a shell composed of a few thousand protein subunits. PduU exists as a hexamer which might further assemble into the flat facets of the polyhedral outer shell of the pdu organelle. This proteinaceous noncarboxysome microcompartment is involved in coenzyme B12-dependent degradation of 1,2-propanediol. The core of PduU is related to the typical BMC domain and its natural oligomeric state is a cyclic hexamer. Unlike other typical BMC domain proteins, the 3D topology of PduU reveals a circular permuted variation on the typical BMC fold which leads to several unique features. The exact functions related to those unique features are still not clear. Another difference is the presence of a deep cavity on one side of the hexamer as well as an intermolecular six-stranded beta barrel that seems to block the central pore that is present in other BMC domain proteins. EutS proteins included in this CD are sequence homologs of PduU. They are encoded within eut operon and may be required for the formation of the outer shell of bacterial eut polyhedral organelles which are involved in the cobalamin-dependent degradation of ethanolamine. Although it has been suggested that EutS might also form hexamers and play similar functional roles in the construction of the eut organelle outer shell at present no experimental evidence directly supports this view.