The core structure of the hexamer is a stacked dimer of trimers. Glu-BDs of the monomers are mainly responsible in the buildup of the core. The relative position of the monomers is such that the rotation about the pivot helix in each monomer is not restricted. The antennae from three subunits within the trimers wrap around each other and undergo conformational changes as the catalytic cleft opens and closes. The antenna serves as an intersubunit communication conduit during negative cooperativity and allosteric regulation.