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A study on the mode of action of clinically relevant antimicrobial peptides
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Resumo(s)
The antimicrobial peptides (AMPs) omiganan (ILRWPWWPWRRK–
NH2) and BP100 (KKLFKKILKYL–NH2) were biophysically studied
with bacterial and mammalian cell membrane models, essentially using
optical spectroscopy techniques. Peptide-membrane binding was interpreted
under a Nernst partition formalism. Both peptides strongly prefer
the anionic bacterial membrane models over the zwitterionic mammalian
ones, justifying, at least in part, higher antibacterial than hemolytic activities.
Deviations to the expected binding behavior were observed at
high bound peptide-to-lipid (P:L) ratios in the membrane whenever anionic
models were used. These deviations could be ascribed to membrane
saturation and occurred with both peptides. The saturation threshold
could be identified for both peptides; the obtained critical P:L ratios were
also consistent with membrane surface charge neutralization. Disruptive
events were observed above the saturation threshold: internalization into
the membrane (omiganan), leakage, membrane aggregation, membrane
surface charge neutralization, and structural reorganization (BP100).
The plausibility of high membrane coverage was evaluated using a
mathematical model devised to estimate the extent of binding under
physiological conditions. Not only is saturation a possible phenomenon
but it was also shown to be a potential requirement for peptide activity.
This hypothesis could be verified using the model with published data
on several AMPs. The model could be further adapted to provide a
means to predict, from simple biophysical parameters (a binding constant
and a critical P:L ratio), the peptide concentration at which antibacterial
activity is triggered. Different methods to implement this prediction are
presented.In vivo measurements using BP100 with Escherichia coli were carried
out to further test the correlation between membrane saturation and bacterial
death. A suitable method to determine the occurrence of binding
saturation with bacteria could not be devised. Nonetheless, bacterial
surface charge did become neutralized by the peptide at the same concentrations
that caused loss of viability, supporting a connection between the
phenomena.
Descrição
Tese de doutoramento, Bioquímica (Biofísica Molecular), Universidade de Lisboa, Faculdade de Ciências, 2010
Palavras-chave
Péptidos Membrana celular Saturação Biofísica molecular Teses de doutoramento - 2010