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Graduate Defense: Marcelo Ayllon

September 23 @ 2:00 pm - 4:00 pm MDT

Dissertation Information

Title: Investigations on the interactions of Streptolysin O and Lysenin with natural and artificial lipid membranes

Program: Doctor of Philosophy in Biomolecular Sciences

Advisor: Dr. Daniel Fologea, Physics

Committee Members: Dr. Juliette Tinker, Biological Sciences, and Dr. Matthew Ferguson, Physics

Abstract

The investigations described in this work are focused on better understanding the interactions between pore-forming toxins (PFTs) and lipid membranes. The necessity of these investigations is justified by the important role of PFTs in infectivity and their potential impact on the development of alternative strategies for mitigating the global burden presented by infectious diseases and the onset of antimicrobial resistance. To achieve our scientific goals, we employed Red Blood Cells (RBCs) as a model for assessing the lytic action of two PFTs, Streptolysin O (SLO), and lysenin. To address the interactions between PFTs and specific membrane moieties as mediators of binding, oligomerization, and lysis, we employed spectrophotometrical assessments of hemolysis in conjunction with affinity measurements by the Kinetics Exclusion Assay (KinExA). The observation that SLO-induced hemolysis was gradually diminished upon cholesterol depletion even when the affinity of SLO for target membranes increased led to the conclusion that a slight reduction in the cholesterol content promotes binding but affects oligomerization into functional pores. Sphingomyelin depletion also led to a reduced hemolytic activity of lysenin but significantly diminished the barrier function of RBC membranes. Prompted by these results, we investigated the use of liposomes as target decoys for SLO and lysenin, capable of diminishing hemolysis in a concentration-dependent manner, which may constitute a complementary or alternative therapeutic approach for infectious diseases in which PFTs act as virulence factors. A direct comparison between the inhibitory effectiveness of monoclonal antibodies and liposomes for SLO clearance indicates the tremendous potential therapeutic applications presented by custom-designed liposomes for aiding in the world-wide fight against bacterial infections.