Use of streptococcal protein G in obtaining crystals of an antibody Fab fragment in complex with a meningococcal antigen.

Crystals have been obtained of an antibody Fab fragment grown in the presence of a single domain from streptococcal protein G and a ten amino-acid peptide corresponding to the P1.7 serosubtype antigen from the human pathogen Neisseria meningitidis. Crystal trials using the Fab fragment and peptide antigen alone were unsuccessful, but the inclusion of a protein G domain provided an additional variable that generated suitable crystals. Crystals are in space group P21 with unit-cell parameters a = 43.60, b = 63.42, c = 89.63 A, beta = 98.58 degrees and a data set has been collected to 2.9 A resolution using synchrotron radiation. The inclusion of protein G is likely to be of general utility for the crystallization of Fab-antigen complexes.