UNCORRECTED PROOF COMMUNICATION Contrasting IgG Structures Reveal Extreme Asymmetry and Flexibility Erica Ollmann Saphire 1 , Robyn L. Stanfield 1 , M. D. Max Crispin 1,2 Paul W. H. I. Parren 3 , Pauline M. Rudd 2 , Raymond A. Dwek 2 Dennis R. Burton 1,3 and Ian A. Wilson 1,4 * 1 Department of Molecular Biology, The Scripps Research Institute, 10550 North Torrey Pines Road, La Jolla, CA 92037 USA 2 Department of Biochemistry University of Oxford, South Parks Road, Oxford OX1 3QU UK 3 Department of Immunology The Scripps Research Institute 10550 North Torrey Pines Road La Jolla, CA 92037, USA 4 The Skaggs Institute for Chemical Biology, The Scripps Research Institute, 10550 North Torrey Pines Road La Jolla, CA 92037, USA The crystal structure of IgG1 b12 represents the first visualization of an intact human IgG with a full-length hinge that has all domains ordered and visible. In comparison to intact murine antibodies and hinge-deletant human antibodies, b12 reveals extreme asymmetry, indicative of the extra- ordinary interdomain flexibility within an antibody. In addition, the struc- ture provides an illustration of the human IgG1 hinge in its entirety and of asymmetry in the composition of the carbohydrate attached to each C H 2 domain of the Fc. The two separate hinges assume different confor- mations in order to accommodate the vastly different placements of the two Fab domains relative to the Fc domain. Interestingly, only one of two possible intra-hinge disulfides is formed. q 2002 Elsevier Science Ltd. All rights reserved Keywords: intact antibody; antibody structure; IgG; hinge region; immune recognition *Corresponding author Antibodies link antigen and immunological effector systems through the use of highly flexible linkers that connect the hypervariable antigen- binding sites (Fabs) to the effector domain (Fc). The extensive flexibility of the antibody molecule permits antibodies to adapt to a vast array of anti- gen shapes and sizes, while retaining a covalent link between the Fab domains and the conserved Fc region that interacts with a limited number of effector systems, such as Fc receptor and complement. 1,2 However, this inherent molecular flexibility of intact antibodies has hindered their crystallization. While well over 200 structures of antibody fragments, mainly Fab and Fab 0 frag- ments, have been determined, crystals of intact antibodies have been reported only ten times: Dob, 3 Mcg, 4 Kol, 5 Zie, 6 mAb 231, 7,8 mAb 4B7, 9 mAb 24–404.1, 10 mAb 61.1.3, 11 IDEC 151, 12 and IgG1 b12. 13 Only seven of these crystals yielded partial or complete structures. No structure has been determined for mAb 4B7, mAb 24–404.1, or IDEC 151. The first two of these crystallized antibodies, Dob and Mcg, are human myeloma proteins of the IgG1 subclass that contain natural hinge deletions and an intra-light chain disulfide bond not present in normal IgG molecules. These hinge-deleted 0022-2836/02/$ - see front matter q 2002 Elsevier Science Ltd. All rights reserved Present address: P. Parren, Genmab, Jenalaan 18a, 3584 CK Utrecht, The Netherlands. E-mail address of the corresponding author: wilson@scripps.edu Abbreviations used: Ig, immunoglobulin; CDR, complementarity-determining region; V H , variable heavy domain; V L , variable light domain; C H , constant heavy domain; C L , constant light domain; mAb, monoclonal antibody; HIV, human immunodeficiency virus; NAG, N-acetyl glucosamine; Man, mannose; Fuc, fucose; Gal, galactose; MALDI-MS, matrix-assisted laser desorption/ ionization mass spectrometry; GU, glucose units. doi:10.1016/S0022-2836(02)00244-9 available online at http://www.idealibrary.com on B w J. Mol. Biol. (2002) 319, 9–18