engleski

SPIN LABELLING STUDY OF IMMUNOMODULATING PEPTIDOGLYCAN MONOMER AND ADAMANTYLTRIPEPTIDES ENTRAPPED INTO LIPOSOMES

The peptides of particular interest for pharmaceutical applications are those which exhibit immunological activity. Compounds comprising the elements of bacterial peptidoglycan structure have been recognized as an important group of immunomodulators. Our studies concern two groups of immunomodulators as potential adjuvants, peptidoglycan monomer (PGM, GlcNAc-MurNAc-L-AIa-D-isoGln-mesoDAP(wNH2)-D-AIa-D-Ala) the natural compound originating from the B. divaricatum peptidoglycan and synthetic adamantyltripeptides D- and L-(adamant-2-yl)-GIy-L-AIa-D-isoGln. We have been examining their encapsulation into liposomes with the aim to possibly increase and optimize their therapeutic effect. The preliminary results showed that encapsulation of PGM and AdTP2 in liposomes improved their adjuvant effect. In order to study the possible interactions between the incorporated peptides and lipid bilayers the electron spin resonance (ESR) was used. ESR is a spin labeling technique, which is based on dynamic sensitivity of the nitroxide label to the time-scale of rotational motions of lipids and proteins in biological membrane. The multilamellar liposomes were spin labelled with n-doxyl stearic acids (n = 5, 7, 12, 16), and dynamic properties of the nitroxide label were studied as a function of the entrapped peptidoglycan monomer and adamantyltripeptides. On the other hand the spin labelled PGM (SL-PGM) was prepared. Two type of studies of the SL-PGM were carried out: a) ESR study of spin labelled PGM at different pH and different temperature. b) The study of interactions of SL-PGM and lipid membranes. The results were shown that the adamantyltripeptides interact with lipids in negatively charged multilamellar liposomes, while peptidoglycan monomer did not directly interact with such lipids. Also, using the SL-PGM we have observed the conformational change in the glycopeptide molecule above 303 K. The conformational change was observed only with the complete molecule and not with the lactylpentapeptide portion generated in alkaline media [1]. [1] Frkanec R., Noethig Laslo V., Vranešić B., Mirosavljević K., Tomašić J., Biochim. Biophys. Acta, (2003) accepted for publication.

liposomes; peptidoglycan monomer; electron spin resonance

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