NMR studies of the RRsrc peptide, a tyrosine kinase substrate

The proton and carbon-13 NMR resonances for the 13-residue synthetic RRsrc peptide were completely assigned using two-dimensional NMR spectroscopy. This peptide contains a tyrosine in position 9 that can be phosphorylated by many tyrosine protein kinases. On the basis of observed nuclear Overhauser enhancements and alpha-proton and alpha-carbon chemical shifts, the peptide appears to interconvert between extended and nascent helical structures. The helical conformation found in aqueous solution is compared with the corresponding structure calculated for the tyrosine 416 site of pp60(src) by homology modeling to the cAMP-dependent protein kinase (PKA) and also to the conformation modelled after the bound form of a PKA-inhibitor peptide.