A bicyclic undecapeptide of sequence cyclo-(Ala(1)-Pro(2)-Asp(3)-Glu(4)-Lys(5)-Ala(6)-Pro(7)-Asp(8)-Asp(9)-Glu(10))-cyclo-(10 gamma --> 5 epsilon)-Gly(11), deigned to mimic the calcium coordination site I of Clamodulin, 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/H2O 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 beta-strands connected by two beta-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 1. The model system, when compares with the reference system (Asp(20)-Glu(31) segment in CaM), shows similar dimensions and an effective superimposition of the reference 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 Ca2+-coordinated site I CD spectra, recorded in TFE solutions, point to a 1:1 stoichimetry for the Ca2+-peptide complex, with an association constant of at least 1 x 10(5) M-1.

Bicyclic Peptides as Models of Calcium Binding Sites. Synthesis and conformation of a Homodetic Undecapeptide

FALCIGNO, LUCIA;D'AURIA, GABRIELLA;
2000

Abstract

A bicyclic undecapeptide of sequence cyclo-(Ala(1)-Pro(2)-Asp(3)-Glu(4)-Lys(5)-Ala(6)-Pro(7)-Asp(8)-Asp(9)-Glu(10))-cyclo-(10 gamma --> 5 epsilon)-Gly(11), deigned to mimic the calcium coordination site I of Clamodulin, 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/H2O 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 beta-strands connected by two beta-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 1. The model system, when compares with the reference system (Asp(20)-Glu(31) segment in CaM), shows similar dimensions and an effective superimposition of the reference 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 Ca2+-coordinated site I CD spectra, recorded in TFE solutions, point to a 1:1 stoichimetry for the Ca2+-peptide complex, with an association constant of at least 1 x 10(5) M-1.
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11588/345223
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