Mutated human IL-18 fusion proteins schema. The His-6 tag indicates the
location of the six histidines fused in the N terminus of the IL-18
precursor propiece. The arrow indicates the ICE cleavage site as
replaced by the factor Xa cleavage site (X). WT indicates wild-type
mature IL-18. E42A indicates Glu-42 to Ala, K89A indicates Lys-89 to
Ala, and E42A + K89A indicates the double mutation. On the basis of WT,
three IL-18 mutants (E42A, K89A, and E42A + K89A) were generated by
two-step PCR.