Nisin interaction with membrane model monitored by fluorescence of pyrene

Abstract

Nisin belongs to a class of antimicrobial polypeptides which are known as Lantibiotics. This polypeptide is positively charged and contains a high content of unusual amino acids, such as lanthionine (DAla-S-Ala,), β-methyllanthionine (DAbu-S-Alas), dehydroalanine (Dha) and dehydrobutyrine (Dhb). They are posttranslational processing products of ribosomally synthesized precursor polypeptides. (1) Fluorescence probe analysis is becoming an important area in biophysical studies of multimolecular aggregates such as micelles and membranes. Studies with pyrene as a fluorescent probe have received special consideration, since this probe has several interesting photophysical properties that can be used for both polarity and viscosity determination of self-assembled membranes. (2) Our group is interested in determine the molecular bases of the bacterial activity of Nisin by using spectroscopic techniques such as fluorescence, FTIR and Raman. As part of these studies, we present here the interaction of Nisin with anionic model membranes composed of dipalmitoilfosfatilglicerol (DPPG), by monitoring the fluorescence spectra changes of pyrene incorporated into the membranes. The evaluation and interpretation of monomer intensity bands and excimermonomer ratio was used for the assessment of changes of polarity in the probe surroundings. These results permit us to conclude that the peptide incorporation increases the rigidity of lipidic membrane.