Abstract
Skin secretions of the Mexican burrowing toad Rhinophrynus dorsalis (Rhinophrynidae) contain the proline-arginine-rich peptide, rhinophrynin-27 (RP-27; ELRLPEIARPVPEVLPARLPLPALPRN) with insulinotropic and immunomodulatory properties, together with a higher concentration of the biologically inactive form, rhinophrynin-33 (RP-33) that constitutes RP-27 extended from its C-terminus by the hexapeptide KMAKNQ. Determination of the conformation of RP-33 by NMR demonstrates that in both water and in a solvent that promotes protein folding (50% trifluoroethanol-water), the majority of the proline residues are found in a polyproline type II helical region. The peptide adopts a horseshoe (U-shaped) conformation with pronounced bends in the molecule of around 100°–120° at Glu 13 and Arg 18. The hexapeptide extension adopts a α-helical conformation. When the hexapeptide is excised to generate RP-27, the molecule adopts an L-shaped conformation with a single bend at Glu 13. A search of protein sequence databases indicated the P-X-P-XXX-P-XXX-P-X-P motif found in RP-27 and RP-33 occurs in a number of proteins although its functional implications are unclear. The data suggest that RP-33 represents a biosynthetic precursor of RP-27 that is activated by a protease cleaving at a single lysine residue of the type previously identified in Xenopus laevis skin secretions.
Original language | English |
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Pages (from-to) | 162-168 |
Number of pages | 7 |
Journal | Biochimie |
Volume | 181 |
Early online date | 30 Dec 2020 |
DOIs | |
Publication status | Published (in print/issue) - 28 Feb 2021 |
Bibliographical note
Funding Information:P.C. would like to acknowledge the Italian Ministry for Education, University and Research (MIUR) and the University of Cagliari for her PhD bursary.
Copyright © 2020 Elsevier B.V. and Société Française de Biochimie et Biologie Moléculaire (SFBBM). All rights reserved.
Keywords
- Amino acid pattern
- Bioactive peptide
- Immunomodulatory
- Insulinotropic
- Nuclear magnetic resonance
- Xenopus