The antibiotic and anticancer active aurein peptides from the Australian Bell Frogs Litoria aurea and Litoria raniformis

Abstract

Seventeen aurein peptides are present in the secretion from the granular dorsal glands of the Green and Golden Bell Frog Litoria aurea, and 16 from the corresponding secretion of the related Southern Bell Frog L. raniformis. Ten of these peptides are common to both species. Thirteen of the aurein peptides show wide-spectrum antibiotic and anticancer activity. These peptides are named in three groups (aureins 1±3) according to their sequences. Amongst the more active peptides are aurein 1.2 (GLFDIIKKIAESF-NH 2 ), aurein 2.2 (GLFDIVKKVVGALGSL-NH 2 ) and aurein 3.1 (GLFDIVKKIAGHIAGSI-NH 2 ). Both L. aurea and L. raniformis have endoproteases that deactivate the major membrane-active aurein peptides by removing residues from both the N-and C-termini of the peptides. The most abundant degradation products have two residues missing from the N-terminal end of the peptide. The solution structure of the basic peptide, aurein 1.2, has been determined by NMR spectroscopy to be an amphipathic a-helix with well-defined hydrophilic and hydrophobic regions. Certain of the aurein peptides (e.g. aureins 1.2 and 3.1) show anticancer activity in the NCI test regime, with LC 50 values in the 10 25 210 24 m range. The aurein 1 peptides have only 13 amino-acid residues: these are the smallest antibiotic and anticancer active peptides yet reported from an anuran. The longer aurein 4 and 5 peptides, e.g. aurein 4.1 (GLIQTIKEKLKELAGGLVTGIQS-OH) and aurein 5.1 (GLLDIVTGLLGNLIVDVLKPKTPAS-OH) show neither antibacterial nor anticancer activity.

Correlation of Three-dimensional Structures with the Antibacterial Activity of a Group of Peptides Designed Based on a Nontoxic Bacterial Membrane Anchor

“…For comparison, we chose aurein 1.2 (9) because it is one of the shortest peptides in the GLFD family of antimicrobial peptides (8). In addition, the C-terminal residue, Phe 13 , of this peptide was found to be essential for anticancer activity (9). As a consequence, peptide A2 was designed by changing Asp 13 of peptide A1 to Phe 13 with Lys 14 -Lys 15 deleted.…”

“…Because all of these peptides start with the sequence GLFD, we may refer to them as the GLFD family. Such a sequence similarity between an E. coli membrane anchor (6) and a group of antimicrobial peptides from Australian frogs (9) suggests that they might have originated from the same ancestral gene a long time ago. Because both types of peptides act on bacterial membranes, one toxic and the other nontoxic, we are curious to learn what determines their functional differences.…”

“…Because both types of peptides act on bacterial membranes, one toxic and the other nontoxic, we are curious to learn what determines their functional differences. Therefore, we have designed a series of peptides (peptides A2, A3, and A4) starting from the bacterial membrane anchor (peptide A1) (6) and ending at a known antibacterial peptide, aurein 1.2 (peptide A5) (9). The sequences and select properties of these peptides are provided in Table I.…”

Antimicrobial peptides from amphibians

“…Magainins (16), ranatuerin-2, temporin families (63,64) and dermaseptins (25) adopt an amphipathic a-helial conformation, either in aqueous solution or upon interaction with membranes of microorganisms (64). However, ranatuerin-1, aurein 1.2 and caerin 1.1 from Australian frog adopt random coil arrangement in aqueous solution and an a-helical structure in membrane mimetic environments (65)(66)(67)(68)(69). The commonly used membrane mimicking solvent is varying mixtures of water and trifluoroethanol (30-50%) or detergent micelles (44,69).…”

“…However, at the same concentration, it kills most human cancer cells; it is also the smallest peptide which has both antibiotic and anticancer activity (65,89). Caerin 1.1 identified from the magnificent tree frog Litoria splendida and green tree frog Litoria caerulea, has an IC 50 value of -10 -6 M against all the major human cancer types (44).…”