Cytotoxicity induced by amyloid proteins is a central aspect of disease progression in many epidemiologically important diseases, including type II diabetes, Alzheimer's, and Parkinson's. Islet amyloid polypeptide (IAPP) forms significant quantities of amyloid fibrils in the pancreata of patients suffering from type II diabetes, and directly contributes to pancreatic β-cell death and progression of the disease. While mature fibrils were initially focused upon as the toxic species, more recent research has implicated membrane permeabilization by pre-amyloid oligomers of IAPP and other amyloid proteins to be the most likely source of cytotoxicity.
While IAPP has been demonstrated to be a membrane permeabilizing protein, there has been significant disagreement as to the specifics of how permeabilization occurs. In this work, we examine and characterize the mechanism by which IAPP induces membrane leakage and cytotoxicity. A variety of ensemble and single-particle measurements are used to examine the initiation of membrane leakage and the evolution of leakage over time. We find that leakage occurs through the stochastic formation of a stable pore that results in all-or-nothing leakage of membrane contents. Pores are initially rapidly leaky, but gradually slow to a stable, equilibrium leakage state. Furthermore, these pores are nucleating for the addition of fresh peptide, allowing it to bypass the stochastic initiation process.
The poration behavior we observe for IAPP shares many similarities with that of the antimicrobial peptide magainin 2. Additionally, the two peptides share several structural characteristics, including an amphipathic α-helical membrane-binding region as well as significant positive charge. Magainin 2 has previously been demonstrated to induce membrane leakage through a tension-mediated mechanism, with poration driven by membrane thinning caused by the binding of amphipathic peptides. We compare the poration behavior and antimicrobial activity of IAPP, magainin 2, and the enantiomeric all D-amino acid D-IAPP. We discover that the three peptides induce membrane leakage and bacterial cytotoxicity through a shared, fully cross-cooperative mechanism. This demonstrates that IAPP is capable of acting as an antimicrobial peptide. It also shows that IAPP and magainin 2 induce membrane poration and cytotoxicity through the same mechanism, potentially unifying the two disparate fields of research.
|Advisor:||Miranker, Andrew D.|
|School Location:||United States -- Connecticut|
|Source:||DAI-B 73/12(E), Dissertation Abstracts International|
|Keywords:||Antimicrobial peptides, Diabetes, Islet amyloid polypeptide, Magainin, Membrane poration|
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