Bacteria have developed a variety of mechanisms for surviving
harsh environmental conditions, nutrient stress and overpopulation.
Paenibacillus dendritiformis produces a lethal protein (Slf) that is able
to induce cell death in neighboring colonies and a phenotypic switch in
more distant ones. Slf is derived from the secreted precursor protein,
DfsB, after proteolytic processing. Here, we present new crystal
structures of DfsB homologues from a variety of bacterial species and a
surprising version present in the yeast Saccharomyces cerevisiae.
Adopting a four-helix bundle decorated with a further three short helices
within intervening loops, DfsB belongs to a non-enzymatic class of the
DinB fold. The structure suggests that the biologically-active Slf
fragment may possess a C-terminal helix rich in basic and aromatic
residues that suggest a functional mechanism akin to that for cationic
antimicrobial peptides.