CRYSTALLIZATION OF DIPHTHERIA-TOXIN

Two new crystal forms (forms III and IV) have been grown of diphtheria toxin (DT), which kills susceptible cells by catalyzing the ADP-ribosylation of elongation factor 2, thereby stopping protein synthesis. Forms III and IV diffract to 2·3 Å and 2·7 Å resolution, respectively. Both forms belong to space group C2; the unit cell parameters for form III are a = 107·3 A ̊, b = 91·7 A ̊, c = 66·3 A ̊ and β = 94·7 ° and those for form IV are a = 108·3 A ̊, b = 92·3 A ̊, c = 66·1 A ̊ and β = 90·4 °. Both forms have one protein chain per asymmetric unit with the dimeric molecule on a twofold axis of symmetry. Form IV is exceptional among all crystal forms of DT in that it can be grown reproducibly. Thus the form IV crystals should yield a crystallographic structure giving insight into the catalytic, receptor-binding and membrane-insertion properties of DT. © 1991.