Diphtheria is a serious upper respiratory tract disease caused by the diphtheria 
toxin (DT) secreted from the bacteria Corynebacterium diphtheriae. Vaccination 
is the best way to protect against this infectious disease. Diphtheria vaccines 
are prepared by isolating, purifying and chemically deactivating DT. Although 
toxoids have been used for decades in immunization, there is still little 
understanding at the molecular level of the process of toxoid preparation, and 
how chemical treatment enhances their immunogenicity. We have undertaken an NMR 
study of the catalytic domain as a first step in understanding the molecular 
details involved in vaccine antigen preparation. Here we report a near complete 
assignment for the backbone and side chain resonances of the diphtheria toxin 
catalytic domain.