The case for class II bacteriocins: a biophysical approach using suicide probes in receptor-free hosts to study their mechanism of action.

RIOS COLOMBO, N.S.; CHALÓN, M.C; DUPUY, F.G.; GONZALEZ, C.F.; BELLOMIO, A.

BIOCHIMIE

ELSEVIER FRANCE-EDITIONS SCIENTIFIQUES MEDICALES ELSEVIER

Lugar: Paris; Año: 2019 vol. 165 p. 183 - 195

0300-9084

Class II bacteriocins are unmodified membrane-active peptides that act over a narrow spectrum of target bacteria. They bind a specific receptor protein on the membrane to form a pore, leading to membrane permeabilization and cell death. However, little is known about the molecular events triggering the pore formation after the bacteriocin recognizes the receptor. It is not clear yet if the pore is the same receptor forced into an open conformation or if the pore results from the bacteriocin insertion and oligomeric assembly in the lipid bilayer. In order to reveal which model is more suitable to explain the toxicity mechanism, in this work we use chimeric peptides, resulting from the fusion of the bitopic membrane protein EtpM with different class 28 II bacteriocins: enterocin CRL35,pediocin PA-1 and microcin V. E. coli strains lacking the specific receptors for these bacteriocins were chosen as expression hosts. As these constructs display a lethal effect when they are heterologously expressed, they are called ?suicide probes?. The results suggest that, indeed, the specific receptor would act as a docking molecule more than as a structural piece of the pore, as long as the bacteriocin is somehow anchored to the membrane. These set of chimeric peptides also represent an in vivo system that allows to study the interaction of the bacteriocins with real bacterial membranes, instead of modelmembranes. Hence, the effects of these suicide probes in membrane fluidity andtransmembrane potential were also assessed, using fluorescence spectroscopy. The data show that the different suicide probes are able to increase phospholipid order and depolarize the membranes of receptor- free bacterial cells.