Calmodulin Binding Peptide Comprising α-Casein Exorphin Sequence

Although not homologous to any known calmodulin binding sequences, α s1 -casein 90−109 (RYLGYLEQLLRLKKYKVPQL), the initial seven residues corresponding to α-casein exorphin sequence, seems to be endowed with the molecular feature characteristic of this class of peptides: a higher proportion of basic and hydrophobic residues. α s1 -Casein 90−109 was synthesized, and its calmodulin binding was examined. α s1 -Casein 90−109 reduced the calmodulin-induced cyclic nucleotide phosphodiesterase activation at the comparable concentration to that previously reported for endogenous opioid peptides such as β-endorphin and dynorphin. α s1 -Casein 90−109 as well as the endogenous opioid peptides shares the common structural motif matching for the interacting domains of calmodulin in the previously proposed complex model, suggesting that these opioid peptides may interact with calmodulin in a similar manner.