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Interaction between positively charged peptides or peptidomimetics and negatively chargedPOPG membranes can be divided into at least two steps. The first step is an electrostaticadsorption process which leads to an increased peptide concentration above the plane ofmembrane. The second step is a hydrophobic adsorption which is characterized bypenetration of the molecule into the lipid bilayer. However, in these studies the electrostaticattraction was omitted in calculation. Assumption, that only hydrophobic effects areimportant in the interaction, is based on the fact that Cystapep 1 analogues are highlyhydrophobic molecules. Moreover, the positive charge of molecules is low and it comesfrom the guanidinium group which possesses special hydrogen bond properties [5]. Thelack of interactions between POPG LUVs and A-89 or A-92 may also indicate thatelectrostatic attraction for the membrane surface does not play important role in the case ofCpV analogues.POPG LUVs constitute the model of bacterial cell membrane. POPG is potentialcell-surface target for the tested peptidomimetics. However, ITC research showed thatinteraction with POPG LUVs is not strongly depend on antibacterial activity of testedcompounds. The most active peptidomimetic from among derivatives tested by ITC studiesA-134 has the lowest value of binding constant. ITC results suggest that the membranedisruption is not a significant mode of action for Cystapep 1 analogs in bacterial system.Probably these peptidomimetics interact with intracellular site of bacteria.We have also performed some experiments using Cvp analogues and POPC LUVs.Research of interaction between this kind of liposomes and peptidomimetics may givesome information about compounds ability to interact with eukaryotic cells. These studiesshowed that none of tested analogues can interact with model of cell membrane ofadvanced organisms. Toxicity studies showed that Cystapep 1 analogues are not toxicagainst eukaryotic cells.The NMR spectra of all investigated molecules show two or more sets of protonresonances. In the NOESY or ROESY spectra it is possible to observe the close contactsbetween Cbz1 and Ckm5 residues for CpV molecule (see Figure 2). For A-92 NOE effectsare observed between Cbz1 and Vax4 residues, but for A-89, A-132, A-134 and for A-142no medium- or long-range contacts are found.Based on the integration of non-overlapping signals in 1D spectra a ratio of major andminor conformations at 303 K was determined. The proportion of minor conformations wasestimated to about 20% for Cystapep 1, 30-40% for A-92, A-132, A-134 and for A-142peptidomimetics. For A-89 it is difficult to measure.The antibacterial investigations show that positions 2, 3 and 4 in the studiedcompounds are very sensitive to replacements. The replacement of very hydrophobic Leuresidue in CpV by less hydrophobic Gly or Pro residues in A-89 and A-92, respectivelylead to the loss of the biological activity. Replacement of position 2, 3 or 4 in CpV byhomoarginine, by norleucine or by benzyloxy group in A-134, A-132 and A-142,respectively lead to the better biological activity.The major and two or more minor conformations in NMR spectra characterize allstudied compounds. It suggests high flexibility of studied peptidomimetics, where veryhigh flexibility could be responsible for very low biological activity. The lower flexibility,with cis-trans isomerization of Arg2-Leu3 peptide bond in A-132, A-134 and in A-142compounds could be responsible for very high antibacterial activity.The structural studies of all peptidomimetics show that close contact between guanidylgroup of Arg2 or Har2 and aromatic ring of Cbz1 and existence of the compacthydrophobic part in the molecules could be responsible for the high antibacterial activity.AcknowledgmentsThe work was supported by Ministry of Science and Higher Education, Grant No.0235/B/H03/2008/35and NN204 023535 and European Social Fund. The calculations were carried out in the TASK inGdansk, Poland.References1. Jasir, A., Kasprzykowski, F., Lindström, V., Schalèn, Grubb, A. Indian J. Med. Res. 119, 74 (2004).2. Jasir, A., et al. APMIS 111, 1004 (2003).3. Wenk, M.R., Seelig, J. J. Phys. Chem. B, 101, 5224 (1997).4. Wenk, M.R., Seelig, J. Biochemistry 37, 3909 (1998).5. Gonçalves, E., Kitas, E., Seelig, J. Biochemistry 44, 2692 (2005).261