Host defence peptides from the skin glands of the Australian Blue Mountains tree-frog Litoria citropa - Solution structure of the antibacterial peptide citropin 1.1

Nineteen citropin peptides are present in the secretion from the granular d orsal glands of the Blue Mountains tree-frog Litoria citropa; 15 of these p eptides are also present in the secretion from the submental gland. Two maj or peptides, citropin 1.1 (GLFDVIKKVASVIGGL-NH2), citropin 1.2 (GLFDIIKKVAS VVGGL-NH2) and a minor peptide, citropin 1.3 (GLFDIIKKVASVIGGL-NH2) are wid e-spectrum antibacterial peptides. The amphibian has an endoprotease which deactivates these membrane-active peptides by removing residues from the N- terminal end: loss of three residues gives the most abundant degradation pr oducts. The solution structure of the basic peptide citropin 1.1 has been d etermined by NMR spectroscopy [in a solvent mixture of trifluoroethanol/wat er (1 : 1)] to be an amphipathic alpha-helix with well-defined hydrophobic and hydrophilic regions. The additional four peptides produced by the dorsa l glands are structurally related to the antibacterial citropin 1 peptides but contain three more residues at their C-terminus [e,g. citropin 1.1.3 (G LFDVIKKVASVIGLASP-OH)]. These peptides show minimal antibacterial activity; their role in the amphibian skin is not known.