The high stability of cruzipain against pH-induced inactivation is not dependent on its C-terminal domain

Unlike mammalian lysosomal cysteine proteases, the trypanosomal cysteine pr otease cruzipain contains a 130-amino acid residue C-terminal domain, in ad dition to the catalytic domain, and it is stable at neutral pH. The endogen ous (with C-terminal domain) and recombinant (without C-terminal domain) cr uzipains exhibit similar stabilities at both acid (k(inac) = 3.1 X 10(-3) s (-1) and 4.4 X 10(-3) s(-1) at pH 2.75 for endogenous and recombinant cruzi pain, respectively) and alkaline pH (k(inac) = 3.0 X 10(-3) s(-1) and 3.7 X 10(-3) s(-1) at pH 9.15 for endogenous and recombinant cruzipain, respecti vely). The pH-induced inactivation, which is a highly pH dependent first or der process, is irreversible and accompanied by significant changes of seco ndary and tertiary structure as revealed by circular dichroism measurements . The different stability of cruzipain as compared to related proteases, is therefore due mainly to the different number, nature and distribution of c harged residues within the catalytic domain and not due to addition of the C-terminal domain. (C) 2000 Federation of European Biochemical Societies.