Antje Pokorny Almeida
Function and Specificity of Membrane-Active Peptides
Essentially all living beings have evolved a primary defense mechanism directed at invading or competing organisms. The molecules that constitute these defensive systems tend to be simple peptides or small proteins that are often specific for a particular target organism. For instance, human saliva contains a class of antimicrobial peptides called defensins that help prevent infestation of the oral cavity by yeasts and bacteria. Interestingly, most antimicrobial and cytolytic peptides bind to their targets without the involvement of specific cell surface receptors. Nevertheless, all of the peptides studied have to interact with the plasma membrane of the target organism to either enter the cell or somehow disrupt membrane integrity. The precise mechanism of these peptides and how the lipid composition of the target membranes modulates their activity, is, to a large extent, still not known. In collaboration with the lab of Paulo Almeida, we study the mechanisms of a series of simple, linear, α-helical peptides and the role of both peptide structure and lipid composition of the target membrane in the process.
The purpose of this project is to understand how lipids typically found in pathogenic bacteria like Staphylococcus aureus influence activity and target specificity of antimicrobial peptides. Why are we interested in S. aureus? Because methicillin-resistant S. aureus strains (MRSA) are becoming a health concern in hospitals world-wide. These highly pathogenic strains have become not only resistant to conventional antibiotics but also to antimicrobial peptides secreted by platelets and neutrophils - and acquired bacterial resistance to antimicrobial peptides has been linked to altered lipid profiles in the bacterial cell membrane.
Bacteria often incorporate lipids not found in eukaryotic cells into their cell membranes. S. aureus, for instance, uses iso- and anteiso-branched lipid acyl chains to maintain cell membrane fluidity. Very little is known about these lipids, their structure, how they are organized in the cell membrane, and how they affect peptide-membrane interactions. We collaborate with the lab of Pamela Seaton on this project.
Other Things I Think About
Cherry, M., Higgins, S., Melroy, H., Lee, H.-S., and Pokorny, A. (2014) Peptides with the same composition, hydrophobicity, and hydrophobic moment bind to phospholipid bilayers with different affinities. Accepted for publication. J. Phys. Chem. B. [DOI: 10.1016/10.1021/jp507289w]
Cox, E, Michalak, A., Pagentine, S., Seaton, P. and Pokorny, A. (2014). Lysylated phospholipids stabilize models of bacterial lipid bilayers and protect against antimicrobial peptides. Biochem. et Biphys. Acta 1838:2198-2204. [DOI: 10.1016/j.bbamem.2014.04.018]
Kreutzberger, A.J. and Pokorny, A. (2012). On the origin of multiphasic kinetics in peptide binding to phospholipid vesicles. J. Phys. Chem. B. 116:951-957. [DOI: 10.1021/jp209080m]
Almeida, P.F. and Pokorny, A. (2012). Interactions of antimicrobial peptides with lipid bilayers. In Lukas Tamm (Ed.), Comprehensive Biophysics (in press). Elsevier.
Dunkin, C., Pokorny, A., Almeida, P., and Lee, H.-S. (2011). Studies of Transportan 10 (Tp10) Interacting with a POPC Lipid Bilayer. J Phys. Chem. B. 115:1188-1198. [DOI: 10.1021/jp107763b]
Kilelee, E, Pokorny, A, Yeaman, M.R., and Bayer, A,S. (2010). Lysyl-Phosphatidylglycerol Attenuates Membrane Perturbation Rather than Surface Association of the Cationic Antimicrobial Peptide 6W-RP-1 in a Model Membrane System: Implications for Daptomycin Resistance. Antimicrob. Agents Chemother. 54:4476-4479. [DOI: 10.1128/AAC.00191-10]
Yandek, L.E., Pokorny, A., and Almeida, P.F. (2009). Wasp mastoparans follow the same mechanism as the cell-penetrating peptide transportan 10. Biochemistry 48:7342-7351. [DOI: 10.1021/bi9008243]
Almeida, P.F. and Pokorny, A. (2009). [Current Topics article] Mechanisms of antimicrobial, cytolytic, and cell-penetrating peptides: from kinetics to thermodynamics. Biochemistry 48:8083-8093. [DOI: 10.1021/bi900914g]
Gregory, S.M., Pokorny, A. and Almeida, P.F. (2009). Magainin 2 Revisited: a Test of the Quantitative Model for the All-or-None Permeabilization of Phospholipid Vesicles. Biophys J. 96:116-131. [DOI: 10.1016/j.bpj.2008.09.017]
Pokorny A., Kilelee EM, Wu D, Almeida PF. (2008). The activity of the amphipathic peptide delta-lysin correlates with phospholipid acyl chain structure and bilayer elastic properties. Biophys J. 95:4748-4755. [DOI: 10.1529/biophysj.108.138701]
Yandek LE, Pokorny A, Almeida PF. (2008). Small changes in the primary structure of transportan 10 alter the thermodynamics and kinetics of its interaction with phospholipid vesicles. Biochemistry 47:3051-3060. [DOI: 10.1021/bi702205r]
Gregory SM, Cavenaugh A, Journigan V, Pokorny A, Almeida PF. (2008). A quantitative model for the all-or-none permeabilization of phospholipid vesicles by the antimicrobial peptide cecropin A. Biophys J. 94:1667-1680. [DOI: 10.1529/biophysj.107.118760]