THE CRYSTAL-STRUCTURE OF THE ANTIBODY N-10-STAPHYLOCOCCAL NUCLEASE COMPLEX AT 2.9 ANGSTROM RESOLUTION

The three-dimensional structure of the antibody N10 Fab fragment compl exed with staphylococcal nuclease (SNase) has been determined to 2.9 A ngstrom resolution. Eighteen residues from six complementarity-determi ning regions (CDR) recognize an epitope of five distinct SNase segment s with a total of 17 residues. The overall shape of the antibody-antig en interface is U-shaped rather than the more or less rectangular inte rface seen in other antibody-protein antigen interfaces. Despite the U -shaped interface, the amount of surface buried in the complex, 828 An gstrom(2) for SNase and 793 Angstrom(2) for N10, is typical of antibod y-protein antigen complexes. Contributing to the shape of the interfac e is the shortest antibody heavy chain-CDR3 loop reported to date, whi ch probably allows access of bulk solvent in the center of the ''U'' i nterface. Another unusual feature of the N10 antibody is the 15 residu e antibody Light chain-CDR1, a length seen in only three other reporte d antibodies. Antibody light chain-CDR1 displays a previously unobserv ed conformation in its distal portion. Finally, although some of the m ovement observed in the antibody-bound SNase may be due to crystal con tacts, it is clear that some side-chain rearrangements are the result of antigen-antibody interaction. (C) 1995 Academic Press Limited