loop_ _pdbx_struct_assembly_auth_evidence.id _pdbx_struct_assembly_auth_evidence.assembly_id _pdbx_struct_assembly_auth_evidence.experimental_support _pdbx_struct_assembly_auth_evidence.details 1 1 'cross-linking' . 2 1 'gel filtration' 'Elutes as a dimer' 3 2 'cross-linking' .