Magainin

The magaiitins are a class of hnear, cationic, faciaUy amphipathic and hehcal antibacterial peptides derived from frog skin [51]. The magaiitins exhibit highly selective and potent antimicrobial activity against a broad spectrum of organisms [52, 53]. As these peptides are faciaUy amphipathic, the magainins have a cationic heli-... 

As such, the magainins provide a useful initial target for peptoid-based peptido-mimetic efforts. Since the helical structure and sequence patterning of these peptides seem primarily responsible for their antibacterial activity and specificity, it is conceivable that an appropriately designed, non-peptide helix should be capable of these same activities. As previously described (Section 1.6.2), peptoids have been shown to form remarkably stable hehces, with physical characterishcs similar to those of peptide polyprohne type-I hehces (e.g. cis-amide bonds, three residues per helical turn, and 6A pitch). A faciaUy amphipathic peptoid helix design, based on the magainin structural motif, would therefore incorporate cationic residues, hydrophobic aromatic residues, and hydrophobic aliphathic residues with threefold sequence periodicity. 

Tab. 1.3 Magainin-mimetic peptoid sequences, and antibacterial and hemolytic activities...

In summary, these recently obtained results demonstrate that certain amphi-pathic peptoid sequences designed to mimic both the helical structure and approximate length of magainin helices are also capable of selective and biomimetic antibacterial activity. These antibacterial peptoids are helical in both aqueous buffer and in the presence of lipid vesicles. Ineffective (non-antibacterial) peptoids exhibit weak, random coil-like CD, with no spectral intensification in the presence of lipid vesicles. Selective peptoids exhibit stronger CD signals in bacterial-mimetic vesicles than in mammalian-mimetic vesicles. Non-selective peptoids exhibit intensely helical CD in both types of vesicles. 

Zasloff, M. Magainins, a class of antimicrobial peptides from Xenopus skin Isolation, characterization of two active forms, and partial cDNA sequence of a precursor. Proc. Nad. Acad. Sci. USA 1987, 84, 5449-5453. 

Bechinger, B. Structure and functions of channel-forming peptides Magainins, cecropins, melittin, and alamethicin. /. Memhr. Biol. 1997, 756, 197-211. 

Tab. 2.9 Antibacterial activities of [Ala ]-magainin II amide and amphiphilic 3i4-helical ent-157b, 83-85) and 2.5,2-helical (158, 159) yS-peptides [175, 234, 248]...

Wakamatsu, K., Takeda, A., Tachi, T., Matsuzaki, K. Dimer structure of magainin 2 bound to phospholipid vesicles. Biopolymers 2002, 64, 314—327. 

Strandberg E, Tremouilhac P, Wadhwani P, Ulrich AS (2009) Synergistic transmembrane insertion of the heterodimeric PGLa/magainin 2 complex studied by solid-state NMR. BBA-Biomembranes 1788 1667-1679... 

Matsuzaki K, Murase O, Fujii N, Miyajima K (1996) An antimicrobial peptide, magainin 2, induced rapid flip-flop of phospholipids coupled with pore formation and peptide translocation. Biochemistry-Us 35 11361-11368... 

Wieprecht, T., M. Beyermann, and J. Seelig. 1999. Binding of antibacterial magainin peptides to electrically neutral membranes thermodynamics and structure. Biochemistry 38 10377-10387. 

Figure 2 Selected stmctures of select host defense peptides representing the major structural classes (a) /3-sheet class (HNP-3 PDB1DFN) (b) linear a-helical class (magainin PDB2MAG) (c) extended class (indolicidin 1G89) (d) cysteine-stabilized 0-/3 (protegrin-3 1PFP). All stmctures were made with MOLMol and the color schema are as follows red/yellow, o-helical propensity aqua, /3-sheet propensity gray, extended or coil.

The amphipathic a-helical class of host defense peptides is the most abundant and most well-characterized class. Upon interaction with the hydrophobic membrane environment, the largely unstructured peptide adopts an amphipathic ct-helical conformation with one helical face containing the majority of the hydrophobic residues, the opposite containing a large proportion of the polar residues. These peptides are often short (<40 amino acids), devoid of cysteine residues, and found to be unstructured or linear in nonhydrophobic environments. Peptides found within this class include the antimicrobial peptide alamethicin, bee venom melittin, the magainins, and the human cathelicidin LL-37. ... 

The effect of increased cationicity on cytotoxicity and antimicrobial activity has been investigated in magainin II. Dathe et al ° have demonstrated that increased cationicity in magainin results in an increased... 

Haukland, H. H., Ulvatne, H., Sandvik, K., and Vorland, L. H. (2001). The antimicrobial peptides lactoferricin B and magainin 2 cross over the bacterial cytoplasmic membrane and reside in the cytoplasm. FEES Lett. 508, 389-393. 

Anticancer squalamine and derivs/steroidal alkal. OSOjH marine Squalus acanthias L., Ch[Pg.163]

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