Toxigenic strains of Clostridium difficile produce two large bacterial toxi
ns called toxins A (TcdA) and B (TcdB), tcdA and tcdB genes are located on
the pathogenicity locus of C, difficile, a unique characteristic of toxigen
ic strains of this species. Intergenic to the two toxin genes is tcdE, a sm
all 501-bp open reading frame of unknown function. Expression of the tcdE g
ene in Escherichia coli caused bacterial cell death. Computational analysis
of the amino acid sequence of TcdE revealed structural features that are s
trikingly similar to a class of bacteriophage proteins called holins, Holin
s are cytolytic proteins that cause lysis of bacterial hosts to effect the
release of progeny phages, Further analysis of the recombinant done express
ing TcdE by transmission electron microscopy confirmed that the site of act
ion of TcdE is on the bacterial cell membrane. The results provide evidence
that TcdE is structurally and functionally similar to holin proteins, TcdE
may function as a lytic protein to facilitate the release of TcdA and TcdB
to the extracellular environment, as these toxins lack signal peptide.