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Calcitonin-like peptides, CGRP-like peptides, Adrenomedullin-like peptides, Frog skin, LC MSn, De novo sequencing
Abstract:
An MS/MS based analytical strategy was followed to solve the complete sequence of two new peptides
from frog (Odorrana schmackeri) skin secretion. This involved reduction and alkylation with two different
alkylating agents followed by high resolution tandem mass spectrometry. De novo sequencing was
achieved by complementary CID and ETD fragmentations of full-length peptides and of selected tryptic
fragments. Heavy and light isotope dimethyl labeling assisted with annotation of sequence ion series. The
identified primary structures are GCD[I/L]STCATHN[I/L]VNE[I/L]NKFDKSKPSSGGVGPESP-NH2 and
SCNLSTCATHNLVNELNKFDKSKPSSGGVGPESF-NH2, i.e. two carboxyamidated 34 residue peptides with
an aminoterminal intramolecular ring structure formed by a disulfide bridge between Cys2 and Cys7.
Edman degradation analysis of the second peptide positively confirmed the exact sequence, resolving I/L
discrimi5nations. Both peptide sequences are novel and share homology with calcitonin, calcitonin gene
related peptide (CGRP) and adrenomedullin from other vertebrates. Detailed sequence analysis as well as
the 34 residue length of both O. schmackeri peptides, suggest they do not fully qualify as either calcitonins
(32 residues) or CGRPs (37 amino acids) and may justify their classification in a novel peptide family
within the calcitonin gene related peptide superfamily. Smooth muscle contractility assays with
synthetic replicas of the S–S linked peptides on rat tail artery, uterus, bladder and ileum did not reveal
myotropic activity.
