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Unblocked statistical-coil tetrapeptides and pentapeptides in aqueous solution: a theoretical study
Jorge A Vila1, Daniel R Ripoll, Héctor A Baldoni
1Instituto de Matemática Aplicada San Luis, Facultad de Ciencias Físico Matemáticas y Naturales, Universidad Nacional de San Luis, CONICET, Ejército de Los Andes 950-5700, Argentina.
Journal of Biomolecular NMR
|January 11, 2003
Summary
This study uses molecular mechanics to model peptide conformations, reconciling experimental data with statistical-coil models by considering pH and sequence effects. These findings help explain anomalies in nuclear magnetic resonance (NMR) spectral parameters.
Area of Science:
- Computational chemistry
- Structural biology
- Biophysics
Background:
- Nuclear magnetic resonance (NMR) studies of peptide and protein conformations require accurate statistical-coil polypeptide models.
- Experimental characterization of statistical-coil states is challenging due to sensitivity to environmental factors like pH and amino acid sequence.
- Discrepancies exist between experimental NMR parameters (e.g., chemical shifts, coupling constants) and theoretical statistical-coil models.
Purpose of the Study:
- To characterize the ensemble of states populated by statistical-coil peptides under varying pH conditions.
- To investigate the influence of pH and amino acid sequence on peptide conformational preferences.
- To resolve discrepancies between experimental NMR data and theoretical models for statistical-coil peptides.
Main Methods:
- Molecular mechanics simulations of unblocked tetra- and pentapeptides.
- Explicit consideration of proton binding/release and its coupling with molecular conformation.
- Inclusion of conformational entropy's contribution to the total free energy.
Main Results:
- Calculated vicinal coupling constants ((3)J(NHalpha)), alpha-proton chemical shifts, and (13)C(alpha) chemical shifts show good agreement with experimental values.
- Theoretical calculations rationalize previously observed anomalies in experimental NMR parameters.
- The study provides insights into how pH and amino acid sequence affect conformational preferences in statistical-coil peptides.
Conclusions:
- Molecular mechanics simulations, incorporating pH effects and conformational entropy, accurately model statistical-coil peptide conformations.
- This approach helps resolve experimental anomalies and improves understanding of peptide behavior in solution.
- The findings are crucial for accurate interpretation of NMR data in peptide and protein structure determination.