Investigating Effects and Determinants of PAP248–286‐Membrane Interactions: Membrane Leakage and Peptide/Lipid Co‐Aggregation

Abstract

Many amyloid‐forming peptides appear to possess potentially beneficial antimicrobial activities. Furthermore, it has been suggested that this previously unrecognized activity may have a role in innate immunity. Antimicrobial peptides, which are important effectors in the innate immune response, can act either directly by inducing membrane leakage and cytolysis, or indirectly through bacterial adhesion inhibition or enhanced phagocytosis via bacterial agglutination. Amyloid‐forming peptides themselves display a variety of membrane‐disrupting and membrane‐remodeling activities, including membrane leakage and vesicle aggregation. In turn, some membranes are known to catalyze amyloid formation. Peptide‐membrane interactions may thus underlie both the pathological activity of amyloid‐forming peptides through their cytotoxicity due to pre‐fibrillar oligomers and their beneficial functions through their direct or indirect antimicrobial activities. Therefore, studying the factors driving the interactions between amyloid‐forming peptides and membranes may be valuable in understanding their roles in both healthy and diseased states.To understand the general principles that govern the interactions of amyloid‐forming peptides with membranes, we use liposomes as model membranes to gain precise control over their size and composition. We have also chosen to focus our studies on an amyloidogenic fragment of prostatic acid phosphatase (PAP248–286). In its amyloid state, this peptide is named “semen‐derived enhancer of viral infection” (SEVI), and greatly increases HIV infectivity. Using spectroscopic techniques, we have discovered that PAP248–286 causes liposome disruption in a charge and dose dependent manner. This dependence is expected given the cationic nature of PAP248–286, and is consistent with similar activities of other pre‐amyloid toxins and antimicrobial peptides. In addition, we have discovered that PAP248–286 forms large, fibrillar lipid‐peptide co‐aggregates. These co‐aggregates have only been observed at specific peptide to lipid ratios with completely anionic liposomes. While this species, which we have termed “messicles”, looks somewhat fibrillar and is Thioflavin T positive, the morphology and kinetics of formation are more reminiscent of an amorphous aggregate than bona fide amyloid. We propose that messicle formation occurs via a mechanism wherein addition of the right amount of negatively charged liposomes completely or partially neutralizes the positive charges on PAP248–286, allowing coated liposomes to self‐associate, and eventually leading to flocculate formation. Since this process would be controlled by the binding affinity of the peptides for the liposomes, messicles might be able to form by this mechanism with other membrane compositions. Considering messicles as another structure in the diverse repertoire of states accessible to PAP248–286 may be important to understanding its function. As amyloid formation and amorphous aggregation occur for other disease‐associated peptides as well, this work could also guide further investigation into their membrane activity and potentially beneficial functions.Support or Funding InformationNSF Graduate Research Fellowship to E.V.This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.