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Mutation of specific acidic residues of the CNF1 T domain into lysine alters cell membrane translocation of the toxin
Author(s) -
Pei Silvia,
Doye Anne,
Boquet Patrice
Publication year - 2001
Publication title -
molecular microbiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.857
H-Index - 247
eISSN - 1365-2958
pISSN - 0950-382X
DOI - 10.1046/j.1365-2958.2001.02596.x
Subject(s) - cytosol , biology , diphtheria toxin , biochemistry , amino acid , lysine , chromosomal translocation , mutant , toxin , cytotoxic t cell , enzyme , gene , in vitro
The Rho‐GTPases‐activating toxin CNF1 (cytotoxic necrotizing factor 1) delivers its catalytic activity into the cytosol of eukaryotic cells by a low pH membrane translocation mechanism reminiscent of that used by diphtheria toxin (DT). As DT, CNF1 exhibits a translocation domain (T) containing two predicted hydrophobic helices (H1–2) (aa 350–412) separated by a short peptidic loop (CNF1‐TL) (aa 373–386) with acidic residues. In the DT loop, the loss of charge of acidic amino acids, as a result of protonation at low pH, is a critical step in the transfer of the DT catalytic activity into the cytosol. To determine whether the CNF1 T domain operates similarly to the DT T domain, we mutated several ionizable amino acids of CNF1‐TL to lysine. Single substitutions such as D373K or D379K strongly decreased the cytotoxic effect of CNF1 on HEp‐2 cells, whereas the double substitution D373K/D379K induced a nearly complete loss of cytotoxic activity. These single or double substitutions did not modify the cell‐binding, enzymatic or endocytic activities of the mutant toxins. Unlike the wild‐type toxin, single‐ or double‐substituted CNF1 molecules bound to the HEp‐2 plasma membrane could not translocate their enzymatic activity directly into the cytosol following a low pH pulse.