Investigating the Importance of the Flexible Hinge in Caerin 1.1:  Solution Structures and Activity of Two Synthetically Modified Caerin Peptides

• Published in: Biochemistry (Easton) 2004-02, Vol.43 (4), p.937-944
• Main Authors: Pukala, Tara L, Brinkworth, Craig S, Carver, John A, Bowie, John H
• Format: Article
• Language: English
• Subjects: Alanine - chemistry; Amino Acid Sequence; Amino Acid Substitution; Amphibian Proteins; Animals; Antimicrobial Cationic Peptides - chemical synthesis; Antimicrobial Cationic Peptides - chemistry; Antimicrobial Cationic Peptides - pharmacology; Anura; Bacteria - drug effects; Bacteria - growth & development; Glycine - chemistry; Hydrogen Bonding; Hydrophobic and Hydrophilic Interactions; Microbial Sensitivity Tests; Molecular Sequence Data; Nuclear Magnetic Resonance, Biomolecular; Proline - chemistry; Protein Conformation; Protein Structure, Secondary; Solutions; Structure-Activity Relationship; Thermodynamics
• ISSN: 0006-2960; 1520-4995
• DOI: 10.1021/bi035760b

Caerin 1.1 is a potent broad-spectrum antibacterial peptide isolated from a number of Australian frogs of the Litoria genus. In membrane-like media, this peptide adopts two α-helices, separated by a flexible hinge region bounded by Pro15 and Pro19. Previous studies have suggested that the hinge region is important for effective orientation of the two helices within the bacterial cell membrane, resulting in lysis via the carpet mechanism. To evaluate the importance of the two Pro residues, they were replaced with either Ala or Gly. The antibacterial activity of these two peptides was tested, and their three-dimensional structures were determined using two-dimensional NMR spectroscopy and restrained molecular dynamics calculations. The resulting structures indicate that the central hinge angle decreases significantly upon replacement of the Pro residues with Gly and to a further extent with Ala. This trend was mirrored by a corresponding decrease in antibiotic activity, further exemplifying the necessity of the hinge in caerin 1.1 and related peptides. In a broader context, the use of Pro, Gly, and Ala variants of caerin 1.1 has enabled the relationship between conformational flexibility and activity to be directly investigated in a systematic manner.