CD, 1H NMR and molecular modeling studies of the interaction of Ca2+ with substance P and Ala7-substance P in a non-polar solvent
✍ Scribed by Xiao-Fei Qi; Boris S. Zhorov; Vettai S. Ananthanarayanan
- Publisher
- John Wiley and Sons
- Year
- 2000
- Tongue
- English
- Weight
- 948 KB
- Volume
- 6
- Category
- Article
- ISSN
- 1075-2617
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✦ Synopsis
The biologically relevant conformation of substance P is likely to be dictated by the lipid milieu wherein the hormone would interact with its receptor. Assuming that specific constraints to the hormone structure may be imparted by its interaction with Ca 2 + ions in the low dielectric lipid medium, the interaction of substance P and its inactive analog, Ala 7 -substance P, has been characterized in a lipidmimetic solvent. Circular dichroism (CD) and NMR spectral methods were employed to study the conformation of the free and Ca 2 + -bound forms of the peptides and the conformational changes that occur on Ca 2 + binding. The results show that both peptides assume a helical structure in the non-polar solvent used, a mixture of acetonitrile and trifluoroethanol. The N-terminal region is, however, less ordered in the analog peptide compared with the native hormone. Ca 2 + addition causes significant conformational changes in both the peptides. However, while substance P binds two Ca 2 + ions in a cooperative manner, Ala 7substance P binds only one Ca 2 + ion with a relatively weaker affinity. Computations of the minimum-energy conformations of the free and Ca 2 -bound peptides were performed using interproton distances derived from nuclear Overhauser enhancement spectra of the two peptides, as well as the information provided by changes in proton chemical shifts caused by Ca 2 + addition. Taken together, the results of this study suggest that differences in the interaction of substance P and Ala 7 -substance P with Ca 2 + in the non-polar milieu, which in turn leads to differences in their Ca 2 + -bound conformations, may be the basis for the differences in their biological potencies.