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Nascent helix in the multiphosphorylated peptide alphaS2-casein(2-20)
N Laila Huq1, Keith J Cross, Eric C Reynolds
1School of Dental Science, The University of Melbourne, 711 Elizabeth Street, Melbourne, 3000, Victoria, Australia.
Summary
Nuclear magnetic resonance (NMR) reveals distinct structures for casein phosphopeptides, even with similar sequences. Calcium ions influence the conformation of these multiphosphorylated motifs, impacting their biological roles.
Area of Science:
- Biochemistry
- Structural Biology
- Biophysics
Background:
- Casein phosphopeptides are crucial in calcium binding and delivery.
- The multiphosphorylated motif is a key feature in casein proteins.
- Understanding peptide structure is vital for elucidating biological function.
Purpose of the Study:
- To determine the sequence-specific NMR assignments for the alphaS2-CN(2-20) peptide.
- To characterize the secondary structure of alphaS2-CN(2-20) in the presence of calcium ions.
- To compare the structural conformations of different casein phosphopeptides with similar motifs.
Main Methods:
- Nuclear Magnetic Resonance (NMR) spectroscopy for spectral assignments and secondary structure determination.
- Analysis of sequential (i,i + 1) and medium-range (i,i + 2/3/4) Nuclear Overhauser Effects (nOes).
- Molecular modeling based on NMR constraints and H alpha chemical shifts.
Main Results:
- NMR assignments were successfully determined for alphaS2-CN(2-20) in the presence of excess Ca2+.
- A nascent helical structure was predicted for residues Ser(P)9 to Glu12.
- Comparison with beta-CN(1-25) and alphaS1-CN(59-79) revealed similar chemical shifts but distinct conformations in Ca2+.
Conclusions:
- Despite sequence similarity, casein phosphopeptides adopt different conformations in the presence of calcium ions.
- The multiphosphorylated motif's conformation is sensitive to the surrounding peptide sequence and calcium ions.
- These findings highlight the structural diversity of casein phosphopeptides and their potential implications in biological systems.