title: Crystals of phosphorylcholine-binding Fab-fragments from mouse myeloma proteins: preparation and x-ray analysis.
abstract: Fab-fragments of several phosphorylcholine-binding mouse-myeloma proteins have been prepared by pepsin digestion; two of these, MOPC 167 and McPC 603, gave large crystals from ammonium sulfate solutions. The Fab-fragment from MOPC 167 crystallizes in a hexagonal space group, but does not diffract to a resolution greater than about 8 A. In contrast, McPC 603 crystals (space group P6(3)) diffract to about 2.7 A. An isotopic double-labeling technique was developed that demonstrated that the 603 crystals bind 1 mol of hapten per mol of Fab-fragment, but with a binding constant significantly lower than that observed in solution. The findings indicate that a three-dimensional model of this homogeneous antigen-binding immunoglobulin can be constructed. Accordingly, a search for heavy-atom derivatives and determination of the primary structure are in progress.
mesh_terms: D000818:Animals; D000937:Antigen-Antibody Reactions; D001666:Binding Sites, Antibody; D002247:Carbon Isotopes; D002794:Choline; D005998:Glycine; D006241:Haptens; D007140:Immunoglobulin Fab Fragments / Q000302:isolation & purification*; D051379:Mice; D009194:Myeloma Proteins / Q000032:analysis* / Q000378:metabolism; D010434:Pepsin A / Q000378:metabolism; D014316:Tritium; D014961:X-Ray Diffraction
chemical_list: D002247:Carbon Isotopes; D006241:Haptens; D007140:Immunoglobulin Fab Fragments; D009194:Myeloma Proteins; D014316:Tritium; D010434:Pepsin A; D002794:Choline; D005998:Glycine