Microcin J25 membrane interaction: selectivity toward gel phase

DUPUY, FERNANDO; AVILA, CESAR LUIS; TORRES-BUGEAU, CLARISA MARÍA; CHEHIN, ROSANA; MORERO, ROBERTO D

Los Cocos, Cordoba

Congreso; XXXVIII Reunion Anual de la Sociedad Argentina de Biofisica; 2009

Microcin J25 (MccJ25) is a 21 aminoacid antibiotic peptide with high hydrophobic character. The N-terminal 8 residue ring formed by a side-chain to backbone bond is threaded by the C-terminal strand of a b-hairpin formed by residues 9-21. The structure is maintained by the tight constraining between the Phe 19- and Tyr 20-side chains and the ring. The MccJ25 antimicrobial mechanism of action involves both the inhibition of the transcriptional activity and the overproduction of deleterious reactive species by targeting the bacterial membrane and the respiratory chain enzymes [1,2]. The later mechanism is observed only in hypersensitive bacteria but their molecular bases were not described in detail. In order to get more insight into the MccJ25 membrane interaction, a tryptophan carrying variant of the peptide, MccJ25 I13W, was studied with FTIR thermograms, fluorescence techniques and molecular dynamics (MD) simulations.Our results suggested that upon insertion of MccJ25 I13W into dipalmitoyl phosphatidylcholine (DPPC) bilayers, the membrane gel to liquid crystalline phase transition was shifted to higher temperatures whereas the hydration of the carbonyl groups at the interface was diminished. Also, the permeability of liposomes with selectivity to small ions was increased. Simulation of MccJ25 I13W embedded on a DPPC bilayer indicated that the b-hairpin region and the residue G12 interacted with the interfacial region of the membrane and reached the maximal depth of insertion, respectively, about 5.5 Å from the bilayer center. As a consequence of the peptide insertion, the average thickness of the lipid bilayer and the order parameter of acyl chains of lipids were increased, in comparison with pure DPPC.These results suggest that MccJ25 could perturb membranes by inducing the formation of ordered lipid domains. As it was previously shown [3], packing defects at the boundaries of lipid domains would explain the increment in the observed membrane permeability.[1] Bellomio A, Vincent P, F. de Arcuri B, Farías R and Morero R, Journal of Bacteriology, 2007, 189(11):4180-96.[2] Dupuy F, Niklison Chirou M, F de Arcuri B, Minahk C and Morero R, Biochimica et Biophysica Acta, 2009, 1790(10):1307-13[3] Epand R and Epand R, Biochimica et Biophysica Acta, 2009, 1788:289-94