Faculty_Page_Antje

Most 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 calleddefensins that help prevent infestation of the oral cavity byyeasts 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 is still largely unknown, although a lot of research has been devoted to the subject. Even more mysterious is how the lipid composition of plasma membranes modulates the activity of these antimicrobial peptides. In collaboration with the lab of Paulo Almeida, we study the mechanisms of a series of simple, linear,a-helical peptides and the role of both peptide structure andlipid composition of the target membrane in the process.

• Bacterial Membranes

The purpose of this project isto understand how lipids typically found in pathogenic bacteria likeStaphylococcus aureus influence activity and target specificity of antimicrobial peptides. Why are we interested inS. aureus? Becausemethicillin-resistant S. aureus strains (MRSA) are becoming a health concern in hospitals world-wide.These highly pathogenic strainshave becomenot 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 ofPamela Seaton on this project.

• Recent Publications

Almeida P.F., Pokorny A., and Hinderliter A. (2005) Thermodynamics of membrane domains. Biochim Biophys Acta. 1720, 1-13.

Pokorny, A., Yandek, L., Elegbede, A., Hinderliter, A., and Almeida, P.F. (2006). Temperature and composition dependence of the interaction ofd-lysin with ternary lipid mixtures. The phase diagram of sphingomyelin/cholesterol/POPC. Biophysical J. 91:2184-2197.

Frazier, M.L., Wright, J.R., Pokorny, A., and Almeida, P.F.F. (2007). Investigation of domain formation in sphingomyelin/cholesterol/POPC mixtures by fluorescence resonance energy transfer and Monte Carlo simulations. Biophys J. 92:2422-2433.

Yandek, L.E., Pokorny, A., Floren, A., Knoelke, K., Langel, U., and Almeida, P.F.F (2006). Mechanism of the cell-penetrating peptide transportan 10 permeation of lipid bilayers. Biophys J. 92:2434-2444.

Gregory, S.M., Cavenaugh, A., Journigan, V., Pokorny, A., and Almeida, P.F. (2008). A quantitative model for the all-or-none permeabilization of phospholipid vesicles by the antimicrobial peptide cecropin A. Biophys. J. 94:1667-1680.

Yandek, L.E, Pokorny, A., and Almeida, P.F. (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.

Pokorny, A., Kilelee, E.M., Wu, D., and Almeida, P.F. (2008). The activity of the amphipathic peptided-lysin correlates with phospholipid acyl chain structure and bilayer elastic properties. Biophys J. 95:4748-4755.

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.

Almeida, P.F. and Pokorny, A. (2009). Mechanisms of antimicrobial, cytolytic, and cell-penetrating peptides: from kinetics to thermodynamics. Biochemistry 48:8083-8093.

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.

• Financial Support

- National Institutes of Health (NIH)

> back to Faculty & Staff	Welcome to the Research Page of Antje Pokorny Almeida
The Lab	• Function and Specificity of Membrane-Active Peptides Most 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 calleddefensins that help prevent infestation of the oral cavity byyeasts 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 is still largely unknown, although a lot of research has been devoted to the subject. Even more mysterious is how the lipid composition of plasma membranes modulates the activity of these antimicrobial peptides. In collaboration with the lab of Paulo Almeida, we study the mechanisms of a series of simple, linear,a-helical peptides and the role of both peptide structure andlipid composition of the target membrane in the process. • Bacterial Membranes The purpose of this project isto understand how lipids typically found in pathogenic bacteria likeStaphylococcus aureus influence activity and target specificity of antimicrobial peptides. Why are we interested inS. aureus? Becausemethicillin-resistant S. aureus strains (MRSA) are becoming a health concern in hospitals world-wide.These highly pathogenic strainshave becomenot 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 ofPamela Seaton on this project. • Recent Publications Almeida P.F., Pokorny A., and Hinderliter A. (2005) Thermodynamics of membrane domains. Biochim Biophys Acta. 1720, 1-13. Pokorny, A., Yandek, L., Elegbede, A., Hinderliter, A., and Almeida, P.F. (2006). Temperature and composition dependence of the interaction ofd-lysin with ternary lipid mixtures. The phase diagram of sphingomyelin/cholesterol/POPC. Biophysical J. 91:2184-2197. Frazier, M.L., Wright, J.R., Pokorny, A., and Almeida, P.F.F. (2007). Investigation of domain formation in sphingomyelin/cholesterol/POPC mixtures by fluorescence resonance energy transfer and Monte Carlo simulations. Biophys J. 92:2422-2433. Yandek, L.E., Pokorny, A., Floren, A., Knoelke, K., Langel, U., and Almeida, P.F.F (2006). Mechanism of the cell-penetrating peptide transportan 10 permeation of lipid bilayers. Biophys J. 92:2434-2444. Gregory, S.M., Cavenaugh, A., Journigan, V., Pokorny, A., and Almeida, P.F. (2008). A quantitative model for the all-or-none permeabilization of phospholipid vesicles by the antimicrobial peptide cecropin A. Biophys. J. 94:1667-1680. Yandek, L.E, Pokorny, A., and Almeida, P.F. (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. Pokorny, A., Kilelee, E.M., Wu, D., and Almeida, P.F. (2008). The activity of the amphipathic peptided-lysin correlates with phospholipid acyl chain structure and bilayer elastic properties. Biophys J. 95:4748-4755. 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. Almeida, P.F. and Pokorny, A. (2009). Mechanisms of antimicrobial, cytolytic, and cell-penetrating peptides: from kinetics to thermodynamics. Biochemistry 48:8083-8093. 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. • Financial Support - National Institutes of Health (NIH)