A conserved motif in transmembrane helix 1 of diphtheria toxin mediates catalytic domain delivery to the cytosol.
A 10-aa motif in transmembrane helix 1 of diphtheria toxin that is conserved in anthrax edema factor, anthrax lethal factor, and botulinum neurotoxin serotypes A, C, and D was identified by blast, clustal w, and meme computational analysis. Using the diphtheria toxin-related fusion protein toxin DAB(389)IL-2, we demonstrate that introduction of the L221E mutation into a highly conserved residue within this motif results in a nontoxic catalytic domain translocation deficient phenotype. To further probe the function of this motif in the process by which the catalytic domain is delivered from the lumen of early endosomes to the cytosol, we constructed a gene encoding a portion of diphtheria toxin transmembrane helix 1, T1, which carries the motif and is expressed from a CMV promoter. We then isolated stable transfectants of Hut102/6TG cells that express the T1 peptide, Hut102/6TG-T1. In contrast to the parental cell line, Hut102/6TG-T1 cells are ca. 10(4)-fold more resistant to the fusion protein toxin. This resistance is completely reversed by coexpression of small interfering RNA directed against the gene encoding the T1 peptide in Hut102/6TG-T1 cells. We further demonstrate by GST-DT140-271 pull-down experiments in the presence and absence of synthetic T1 peptides the specific binding of coatomer protein complex subunit beta to this region of the diphtheria toxin transmembrane domain.
Ratts
Ryan
R
Department of Medicine, Section of Molecular Medicine, Boston University School of Medicine, Boston, MA 02118, USA.
Trujillo
Carolina
C
Bharti
Ajit
A
vanderSpek
Johanna
J
Harrison
Robert
R
Murphy
John R
JR
D000595:Amino Acid Sequence; D000818:Animals; D020134:Catalytic Domain; D017124:Conserved Sequence; D003600:Cytosol / Q000378:metabolism*; D004167:Diphtheria Toxin / Q000737:chemistry* / Q000378:metabolism; D008969:Molecular Sequence Data; D021381:Protein Transport; D011817:Rabbits
D004167:Diphtheria Toxin