 The E3 binding protein directly interacts with the dihydrolipoamide transacetylase (E2) core, anchoring it to the complex.E3BP binds the I domain of E2 by its C-terminal I' domain.The composition of E2.E3BP was thought to be 60 E2 plus approximately 12 E3BP, however, equilibrium sedimentation and small angle x-ray scattering studies showed that the E3BP/E2 binding complex has a lower mass than the E2 subunit alone.