Assembly and molecular transport across the bacterial PduA shell proteins in the Pdu microcompartment. The 1,2-propanediol utilization (Pdu) pathway catabolizes 1,2-propanediol via a toxic aldehyde intermediate. PduA is a BMC shell protein of the Pdu microcompartment and is the route of substrate (1,2-propanediol) entry. The thick line, running from −z to +z, indicates the molecular six-fold axis; the pair of broken lines parallel to this axis demarcate the radial limits (in our cylindrical coordinate system). Inset shows a zoomed in view of the PduA hexamer pore (cartoon) showing residue S40 lining the pore (radius 2.8Å).