Molecular Cloning and Characterization of cDNAs Encoding Biosynthetic Precursors for the Antimicrobial Peptides Japonicin-1Ja, Japonicin-2Ja, and Temporin-1Ja in the Japanese Brown Frog, Rana japonica

摘要

Using a combination of reverse-transcription polymerase chain reaction and the 5'- and/or 3'-rapid amplification of cDNA ends, we cloned, from a Japanese brown frog (Rana japonica) skin total RNA preparation, cDNAs encoding biosynthetic precursors for the antimicrobial peptides (AMPs) japonicin-1Ja (FFPIGVFCKIFKTC), japonicin-2Ja (FGLPMLSILPKALCILLKRKC), and temporin-1Ja (ILPLVGNLLNDLL. NH2). These peptides were previously isolated from an extract of R. japonica skin. The present study is the first report to describe the molecular cloning of the cDNA encoding a japonicin-2 family peptide. The nucleotide and deduced amino acid sequence analyses revealed that the hypothetical precursor protein of japonicin-2Ja, as well as japonicin-1Ja and temporin-1Ja, is organized similarly to those of typical amphibian AMP precursors, with a highly conserved signal peptide, a relatively well conserved intervening sequence, and a hypervariable AMP mature region. Antimicrobial assays for synthetic replicates of cyclic and linear japonicin-2Ja revealed that the intramolecular disulfide bond is necessary for activity. A semi-quantitative analysis by real-time RTPCR using TaqMan probes revealed that the relative values of preprojaponicin-2Ja mRNA expression levels in the skin, skeletal muscle of hind leg, kidney, testis, small intestine, and stomach total RNA sample specimens in adult R. japonica were 6.5 x 10(5), 9.6, 2.0, 1.6, 1.6, and 1.0, respectively. The presence of preprojaponicin-2Ja mRNAs in the cytoplasm of glandular cells in R. japonica dorsal skin glands was demonstrated by means of in situ hybridization using digoxigenin-labeled cRNA probes for the precursor.