Post-translational amino acid racemization in the frog skin peptide deltorphin I in the secretion granules of cutaneous serous glands

• Published in: European journal of cell biology 2006-01, Vol.85 (1), p.25-34
• Main Authors: Auvynet, Constance, Seddiki, Nabila, Dunia, Irene, Nicolas, Pierre, Amiche, Mohamed, Lacombe, Claire
• Format: Article
• Language: English
• Subjects: Amino Acid Sequence; Amino Acids - chemistry; Amino Acids - metabolism; Amphibian Proteins - chemistry; Animals; Antimicrobial Cationic Peptides - chemistry; Anura - metabolism; Chemical Sciences; d-amino acid-containing peptide; Deltorphin; Dermaseptin; Frog skin; Molecular Sequence Data; Oligopeptides - chemistry; Oligopeptides - metabolism; Organic chemistry; Phyllomedusa; Protein Processing, Post-Translational; Protein Transport; Racemization; Secretory Vesicles - metabolism; Skin - cytology; Skin - metabolism; Skin - ultrastructure
• ISSN: 0171-9335; 1618-1298
• DOI: 10.1016/j.ejcb.2005.09.022

The dermal glands of the South American hylid frog Phyllomedusa bicolor synthesize and expel huge amounts of cationic, α-helical, 24- to 33-residue antimicrobial peptides, the dermaseptins B. These glands also produce a wide array of peptides that are similar to mammalian hormones and neuropeptides, including a heptapeptide opioid containing a d-amino acid, deltorphin I (Tyr– dAla–Phe–Asp–Val–Val–Gly NH 2). Its biological activity is due to the racemization of l-Ala2 to d-Ala. The dermaseptins B and deltorphins are all derived from a single family of precursor polypeptides that have an N-terminal preprosequence that is remarkably well conserved, although the progenitor sequences giving rise to mature opioid or antimicrobial peptides are markedly different. Monoclonal and polyclonal antibodies were used to examine the cellular and ultrastructural distributions of deltorphin I and dermaseptin B in the serous glands by immunofluoresence confocal microscopy and immunogold-electron microscopy. Preprodeltorphin I and preprodermaseptins B are sorted into the regulated pathway of secretion, where they are processed to give the mature products. Deltorphin I, [ l-Ala2]-deltorphin I and dermaseptin B are all stored together in secretion granules which accumulate in the cytoplasm of all serous glands. We conclude that the l- to d-amino acid isomerization of the deltorphin I occurs in the secretory granules as a post-translational event. Thus the specificity of isomerization depends on the presence of structural and/or conformational determinants in the peptide N-terminus surrounding the isomerization site.