Arg-Gly-Tyr-Ser-Leu-Gly is corresponding to the sequence of residues from 21 through 26 in lysozyme. Arg-Gly-Tyr-Ser-Leu-Gly can be used as a substrate for the protein kinase, and phosphorylated at serine residue by protein kinase.
References:
[1]. Kemp BE, et al. Synthetic hexapeptide substrates and inhibitors of 3':5'-cyclic AMP-dependent protein kinase. Proc Natl Acad Sci U S A. 1976 Apr;73(4):1038-42.