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Conformational study of small peptides and their circular dichroism spectra

Opioid peptides are known to be associated with many physiological features such as pain mediation, opiate dependence, and euphoria. They are also known to possess affinity for several distinct receptors, implying an ability to assume different shapes for different purposes. Particularly important in this respect is the anti-cancer activity of Opioid Growth Factor (OGF). Improved effects have been seen for its unnatural analogues, which have been proposed to have a structural origin. Using replica exchange molecular dynamics, we have investigated the structural preferences of these peptides. The simulations were performed in explicit trifluoroethanol, as a prototypical low polarity environment. In order to provide a direct link with experiment, circular dichroism spectra of the peptides were calculated using a QM/MM approach in which the peptide was treated quantum mechanically, while the effect of the solvent was included classically.

computational chemistry; opioid peptides; REMD; circular dichroism; QM/MM

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