Gaegurin 5 (GGN5) is a cationic 24-residue anti-microbial peptide isolated from the skin of a Korean frog, Rana rugosa. It contains a central proline residue and an intra-residue disulphide bridge in its C-terminus, which are common to the anti-microbial peptides found in Ranidae. We determined the solution structure of GGN5 bound to SDS micelles for the first time and investigated the role of proline, cysteine and a disulphide bridge on the structure and activity of GGN5. GGN5 adopts an amphipathic α-helical structure spanning residues 3—20 kinked around Pro-14, which allows the hydrophobic residues to reside in the concave helical region, and a disulphide-bridged loop-like conformation in its C-terminus. By replacement of proline with alanine (PAGGN5), a straight and rigid helix was formed in the central region and was more stable than the kinked helix. Reduction of a disulphide bridge in the C-terminus (GGN5SH) maintained the loosely ordered loop-like conformation, while the replacement of two cysteines with serines (CSGGN5) caused the C-terminal conformation to be completely disordered. The magnitude of anti-microbial activity of the peptides was closely related to their helical stability in the order PAGGN5>GGN5>GGN5SH>CSGGN5, suggesting that the helical stability of the peptides is important for anti-microbial activity. On the other hand, the significant increase of haemolytic activity of PAGGN5 implies that a helical kink of GGN5 could be involved in the selectivity of target cells. The location of GGN5 and PAGGN5, analysed using paramagnetic probes, was mainly at the surface of SDS micelles, although the location of the N-terminal region was slightly different between them.
- helical kink
- loop-like conformation
- micelle-bound peptide fold
- solution structure
Abbreviations used: DPC, dodecylphosphocholine; DTT-d10, perdeuterated dithiothreitol; DQF, double-quantum filtered; GGN, gaegurin; GGN5SH, reduced form of GGN5; CSGGN5, Cys-18/Cys-24→Ser-substituted form of GGN5; PAGGN5, Pro-14→Ala-substituted form of GGN5; RMSD, root-mean-square deviation; methanol-d4, perdeuterated methanol; SDS-d25, perdeuterated SDS; 2D, two-dimensional; TFE, trifluoroethanol; NOESY, nuclear Overhauser enhancement spectroscopy; NOE, nuclear Overhauser effect.
- The Biochemical Society, London ©2002