Kr. Klimpel et al., ANTHRAX TOXIN LETHAL FACTOR CONTAINS A ZINC METALLOPROTEASE CONSENSUSSEQUENCE WHICH IS REQUIRED FOR LETHAL TOXIN ACTIVITY, Molecular microbiology, 13(6), 1994, pp. 1093-1100
Comparison of the anthrax toxin lethal factor (LF) amino acid sequence
with sequences in the Swiss protein database revealed short regions o
f similarity with the consensus zinc-binding site, HEXXH, that is char
acteristic of metalloproteases. Several protease inhibitors, including
bestatin and captopril, prevented intoxication of macrophages by leth
al toxin. LF was fully inactivated by site-directed mutagenesis that s
ubstituted Ala for either of the residues (H-686 and H-690) implicated
in zinc binding. Similarly, LF was inactivated by substitution of Cys
for E-687, which is thought to be an essential part of the catalytic
site. In contrast, replacement of E-720 and E-721 with Ala had no effe
ct on LF activity. LF bound Zn-65 both in solution and on protein blot
s. The Zn-65 binding was reduced for several of the LF mutants. These
data suggest that anthrax toxin LF is a zinc metallopeptidase, the cat
alytic function of which is responsible for the lethal activity observ
ed in cultured cells and in animals.