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Bicyclic peptides as models of calcium binding sites: Synthesis and conformation of a homodetic undecapeptide
Author(s) -
Oliva R.,
Falcigno L.,
D'Auria G.,
Saviano M.,
Paolillo L.,
Ansanelli G.,
Zanotti G.
Publication year - 2000
Publication title -
biopolymers
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.556
H-Index - 125
eISSN - 1097-0282
pISSN - 0006-3525
DOI - 10.1002/(sici)1097-0282(200006)53:7<581::aid-bip5>3.0.co;2-c
Subject(s) - chemistry , antiparallel (mathematics) , stereochemistry , crystallography , bicyclic molecule , calmodulin , nuclear magnetic resonance spectroscopy , peptide , cyclic peptide , stoichiometry , sequence (biology) , calcium , organic chemistry , biochemistry , quantum mechanics , magnetic field , physics
Abstract A bicyclic undecapeptide of sequence cyclo ‐(Ala 1 ‐Pro 2 ‐Asp 3 ‐Glu 4 ‐Lys 5 ‐Ala 6 ‐Pro 7 ‐Asp 8 ‐Ser 9 ‐Glu 10 )‐ cyclo ‐(10γ → 5ε)‐Gly 11 , designed to mimic the calcium coordination site I of Calmodulin, has been synthesized and its conformation and calcium binding properties have been investigated by means of CD and nmr spectroscopy. The nmr analysis of the free peptide, carried out in DMSO and in TFE/H 2 O at different pH values, shows the presence in solution of one stable conformer, exhibiting trans configuration around both Proline residues. The nmr results in both solvents suggest for the molecule a rectangular shape constituted by two antiparallel β‐strands connected by two β‐turns. Interproton distances, evaluated by NOE contacts, have been used to obtain feasible models by means of Restrained Molecular Dynamic (RMD). The average models from RMD calculations, for both solvents, exhibit good analogies with Calmodulin site I. The model system, when compared with the reference system (Asp 20 ‐Glu 31 segment in CaM), shows similar dimensions and an effective superimposition of the respective sequence segments Ala 1 ‐Glu 4 and Thr 28 ‐Glu 31 . The remaining segments of the model peptide exhibit a bending that is intermediate between that of the free and Ca 2+ ‐coordinated site I. CD spectra, recorded in TFE solutions, point to a 1:1 stoichiometry for the Ca 2+ ‐peptide complex, with an association constant of at least 1 × 10 5 M −1 . © 2000 John Wiley & Sons, Inc. Biopoly 53: 581–595, 2000