An LeFollow

Document Type

Thesis

Degree Name

Master of Science (MSc)

Department

Chemistry

Program Name/Specialization

Biological and Chemical Sciences

Faculty/School

Faculty of Science

First Advisor

Masoud Jelokhani-Niaraki

Advisor Role

Supervisor

Second Advisor

Matthew Smith

Advisor Role

Co-supervisor

Abstract

Cell-penetrating peptides (CPPs) interact with biological membranes, undergo cellular intake/uptake, and may act as potential drug delivery agents. Understanding the molecular interactions of these peptides with membranes contributes to gaining a better knowledge of their potential use in medical and pharmaceutical applications to improve human health. The current research focuses on understanding the mechanisms of a CPP in interaction with different model phospholipid membranes. The peptide penetratin (primary sequence: RQIKIWFQNRRMKWKK) is an example of a CPP that can interact with and pass through biological membranes. The current thesis provides spectroscopic and calorimetric evidence that penetratin associates with lipid membranes. Circular dichroism (CD) spectra show that during interactions of penetratin and a protected analogue with model lipid membranes, their structures change from unordered in buffer solution and in the presence of PC lipid vesicles to α-helical in the presence of PE/PG and PC/PG lipid vesicles. The CD spectra of the peptide at relatively low concentrations in both PE/PG and PC/PG lipid vesicles also provide evidence of self-association in these lipid environments. Fluorescence spectroscopy reveals that the peptide inserts deeper into the hydrophobic region of the lipid membranes as compared to the aromatic analogues of the peptide that were tested. The effect of aromaticity on penetratin’s mechanism of interaction with model lipid membranes reveals that the two Trp residues assist the peptide to insert deeper into the hydrophobic region of the membrane. Isothermal titration calorimetry (ITC) studies demonstrate that this positively charged peptide is attracted to the negatively charged phosphate groups during the interaction with the lipid membranes. With a possibility of inserting into the hydrophobic region of the lipid membrane, the α-helical penetratin could self-associate, which in turn could cause disruption of the membrane structure.

Convocation Year

2020

Convocation Season

Fall

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