Biologically active peptides caged on tyrosine.

We have demonstrated the feasibility of preparing caged peptides by derivatizing a single amino acid side chain in peptides up to 20 amino acids long. Two peptides are illustrated whose activities are reduced by nearly 2 orders of magnitude using this caging approach. The specific strategy described here of derivatizing tyrosine side chains with a charged caging moiety should be generally applicable in the preparation of caged peptides that have a critical tyrosine residue (e.g., LSM1) or that have critical hydrophobic patches (e.g., RS-20). Other amino acid side chains are also accessible via this caging strategy. Derivatives of threonine, serine, lysine, cysteine, glutamate, aspartate, glutamine, and asparagine can be prepared and site specifically inserted into peptides in an analogous manner. The caged peptides synthesized and purified by the methods described here are compatible with biological samples, including living cells, and have been used to demonstrate the central importance of calmodulin, MLCK, and, by inference, myosin II in ameboid locomotion in polarized eosinophil cells. Photoactivation of peptides within cells should provide a wealth of new information in future investigations by allowing specific protein activities to be knocked out in an acute and spatially defined way.