INTERACTION OF INDOLICIDIN WITH MODEL LIPID BILAYERS - FTIR-ATR SPECTROSCOPIC STUDY

An attempt has been made using Fourier transform infrared-attenuated t otal reflection (FTIR-ATR) spectroscopy to see the molecular level int eraction between indolicidin, a tridecapeptide known to possess antimi crobial activity, and model phospholipid bilayers. Initially, model li pid bilayers were assembled on ZnSe plates with compounds of dipalmito ylphosphatidic acid (DPPA), dipalmitoylphosphatidylcholine (DPPC), and dipalmitoylphosphatidylglycerol (DPPG) using the Langmuir-Blodgett (L B) method. From the FTIR-ATR dichroic ratios measured with and without rotation of the ATR plates, the LB lipid bilayers seemed to be descri bed in terms of a uniaxial orientational model. Along with a cyclovolt ammetry measurement, the ATR spectra dictated that indolicidin molecul es were readily incorporated inside the acyl chains of the lipid bilay ers. Furthermore, from the infrared absorption frequencies of amide I bands, indolicidin molecules that consisted of ill-defined random-coil structures in an aqueous medium appeared to adopt a 3(10)-helical con formation inside the lipid bilayers. This view was in good agreement w ith the electronic circular dichroism observed for PC (+10% cardiolipi n) vesicles mixed with an indolicidin solution.