Selection of targeted biological modifiers from a bacteriophage library of random peptides. The identification of novel calmodulin regulatory peptides.

The interaction of short amino acid sequences is the basis of molecular recognition and biological regulation in many cellular systems. Libraries of random peptides provide an approach to identify peptides that can be used to modulate, in a targeted fashion, the function of specific gene products. We have used a library of random peptides designed and constructed in the M13 bacteriophage to select calcium-dependent calmodulin binding-peptides. Twenty-eight independent sequences were obtained; all contained a tryptophan within the fifteen-amino acid insert. In 11 sequences, the tryptophan was located in the first possible variable position of the inserted sequence and was followed by a proline. The tryptophan-proline combination was also present in six additional isolates but at various other positions within the peptide insert. Synthetic peptides, representative of the calmodulin binding sequences, bound to calmodulin in a calcium-dependent fashion, competed with known calmodulin inhibitors and, when introduced via a patch pipette, inhibited calcium-activated chloride conductance of the colonic epithelial cell line, T84. This report demonstrates the utility of identifying modifiers of biological function and should prove to be a valuable approach in understanding the cellular role of proteins of unknown function.