Crystallization of an antitumour antibody SM3 complexed with a peptide epitope

SM3 antibody binds to a tumour-associated epitope on polymorphic epithelial mucin (PEM). Crystals of the Fab fragment of SM3 in complex with a peptide antigen were obtained by vapour diffusion against mother liquor containing acetate buffer, pH 6.5, cadmium chloride and polyethylene glycol (PEG) 4000 as precipitating agent. Crystals belong to the monoclinic space group P2₁ with cell dimensions a = 42.2, b = 83.9, c = 64.5 Å and β = 93.4°. One Fab-antigen complex is present in the asymmetric unit. Diffracted intensities up to 1.95 Å resolution have been measured from a frozen crystal using synchrotron radiation.