Shuiping So, Jiaxin Wu, Gangxiong Huang
Mar 28, 2003
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1
Influential Citations
40
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Journal
The Journal of Biological Chemistry
Abstract
The second extracellular loop (eLP2) of the thromboxane A2 receptor (TP) had been proposed to be involved in ligand binding. Through two-dimensional1H NMR experiments, the overall three-dimensional structure of a constrained synthetic peptide mimicking the eLP2 had been determined by our group (Ruan, K.-H., So, S.-P., Wu, J., Li, D., Huang, A., and Kung, J. (2001) Biochemistry 40, 275–280). To further identify the residues involved in ligand binding, a TP receptor antagonist, SQ29,548 was used to interact with the synthetic peptide. High resolution two-dimensional 1H NMR experiments, NOESY, and TOCSY were performed for the peptide, SQ29,548, and peptide with SQ29,548, respectively. Through completed 1H NMR assignment and by comparing the different spectra, extra peaks were observed on the NOESY spectrum of the peptide with SQ29,548, which implied the contacts between residues of eLP2 at Val176, Leu185, Thr186, and Leu187 with SQ29,548 at position H2, H7, and H8. Site-directed mutagenesis was used to confirm the possible ligand-binding sites on native human TP receptor. Each of the four residues was mutated to the residues either in the same group, with different structure or different charged. The mutated receptors were then tested for their ligand binding activity. The receptor with V176L mutant retained binding activity to SQ29,548. All other mutations resulted in decreased or lost binding activity to SQ29,548. These mutagenesis results supported the prediction from NMR experiments in which Val176, Leu185, Thr186, and Leu187 are the possible residues involved in ligand binding. This information facilitates the understanding of the molecular mechanism of thromboxane A2 binding to the important receptor and its signal transduction.