 Additionally, these studies showed that E3 binds to E2.E3BP outside the central dodecahedron of the PDH complex, and that this interaction creates a lower binding affinity for the E1 subunit.Together, these data support a substitution model, in which the smaller E3BP subunits replace the E2 subunits rather than adding to the 60-mer entire complex.The specific model illustrates 12 I domains of E2 being substituted by 12 I' domains of E3BP, thereby forming 6 dimer edges that are symmetrically located in the dodecahedron structure.