RESUMO
Cytolysin A (ClyA) is a water-soluble alpha pore-forming toxin that assembles to form an oligomeric pore on host cell membranes. The ClyA monomer possesses an α-helical bundle with a ß-sheet subdomain (the ß-tongue) previously believed to be critical for pore assembly and/or insertion. Oligomerization of ClyA pores transforms the ß-tongue into a helix-turn-helix that embeds into the lipid bilayer. Here, we show that mutations of the ß-tongue did not prevent oligomerization or transmembrane insertion. Instead, ß-tongue substitution mutants yielded pores with decreased conductance while a deletion mutation resulted in pores that rapidly closed following membrane association. Our results suggest that the ß-tongue may play an essential structural role in stabilizing the open conformation of the transmembrane domain.