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P.L. Jackson, D.D. Muccio, J.L. Haddox, R.R. Pfister; NMR and CD Spectroscopy Studies on the Interactions of a Tetrameric RTR Peptide and the Chemoattractant Ac-PGP . Invest. Ophthalmol. Vis. Sci. 2003;44(13):1399.
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Purpose: Previous studies have demonstrated that Ac-PGP is present in the alkali-injured cornea and that this tripeptide is a neutrophil chemoattractant in vitro and in vivo. Other studies have demonstrated that a tetrameric RTR peptide (designed by Molecular Recognition Theory) inhibits Ac-PGP induced neutrophil activation in vitro and reduces corneal ulceration in the alkali-injured cornea. Here we propose to determine if the tetrameric RTR peptide and Ac-PGP interact in solution. Methods: Solution state 1 H Nuclear Magnetic Resonance (NMR) spectroscopy and circular dichroism (CD) spectroscopy were used to study the interactions of the tetrameric RTR peptide and Ac-PGP under a variety of solution conditions. Experiments were performed where Ac-PGP was titrated into a solution of the tetrameric RTR peptide or in a reciprocal manner. The titrations were performed at pH values ranging from 4.0 to 7.4 and in the presence or absence of salt. Results: Tetrameric RTR peptide exists as a very flexible peptide in solution. The RTR arms of the peptide appear to be highly dynamic. Ac-PGP exists as a mixture of four conformers in solution due to cis/trans isomerization around the X-Pro amide bond. In titrations, we observed chemical shift changes for distinct peaks on both peptides, coupling pattern changes and an increased intensity of the amide peaks of the tetrameric RTR peptide. These changes are consistent with the two peptides interacting with one another in solution. Conclusions: We conclude that the tetrameric RTR peptide is capable of interaction with Ac-PGP and that this interaction may be responsible for the reduction of corneal ulceration in the alkali-injured eye.
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