Modification of pertussis toxin

A method for producing a modified form of at least a portion of pertussis holotoxin, comprising:

• (a) forming a crystalline complex between at least a portion of pertussis holocoxin and a molecule capable of complexing with the holotoxin, wherein said molecule is selected from the group consisting of an adenine nucleotide, NAD, a substantially non-hydrolysable analog of NAD, a GTP-binding protein, and .alpha.-subunit of a GTP-binding protein and a C-terminal fragment of a .alpha.-subunit of a GTP binding protein;
• (b) determining a three-dimensional structure of the comnplex by X-ray crystallography;
• (c) analysing the structure to identify at least one amino acid residue of the at least a portion of pertussis holatoxin interacting with the molecule;
• (d) effecting mutagensis of a nucleotide sequence encoding the at least a portion of the pertussis holotoxin to remove or replace a codon for the at least one amino acid and/or to insert at least one codon adjacent the codon for the at least one amino acid to produce a mutant nucleotide sequence;
• and
• (e) expressing the mutant nucleotide sequence to produce the modified form of at least a portion of pertussis holocoxin.