Crystal structure of an idiotype-anti-idiotype Fab complex

Abstract

Anti-idiotypic monoclonal antibody 409.5.3 is raised against an antibody that neutralizes feline infectious peritonitis virus. This antibody, used as an immunogen, elicits the production of anti-anti-idiotypic antibodies that in turn neutralize the virus. The crystal structure of the complex between anti-idiotypic Fab 409.5.3 and idiotypic Fab fragment of virus-neutralizing antibody has been solved by molecular replacement using real-space Patterson search and filtering by Patterson correlation-coefficient refinement. The structure has been refined to an R value of 0.21 based on 21.310 unique reflections between 40.0 and 2.9 A. The three-dimensional structure reveals extensive, specific interactions that involve 118 van der Waals contacts and at least 9 probable hydrogen bonds. The two Fabs are rotated 61° with respect to each other around the approximate long axis of the complex and are within 26° of being aligned along their major axes.