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. Author manuscript; available in PMC: 2009 Oct 7.
Published in final edited form as: Biochemistry. 2008 Sep 17;47(40):10649–10656. doi: 10.1021/bi801128d

Figure 1. The different oligomeric assemblies of PBGS.

Figure 1

The PBGS equilibrium ensemble of quaternary structure forms is illustrated using homology models of pea PBGS. For most species, the asymmetric unit of the crystal structure is an asymmetric homo-dimer (3, 5, 6, 27). The hexamer and its asymmetric unit, the detached dimer (based on PDB code 1PV8) are shown in two shades of blue. The octamer and its asymmetric unit, the hugging dimer (based on PDB code 1GZG) are shown in two shades of pink. For the octamer, the dimers assemble at a 90° rotation around a central axis; for the hexamer, the dimers assemble at a 120° rotation around a central axis. The octamer contains a phylogenetically variable binding site for an allosteric magnesium ion. This ion binds to the arm-to-barrel interface that is unique to the octamer; the allosteric magnesium binding site is not present in the hexamer (3, 22).