Mutagenesis and selection of PDZ domains that bind new protein targets

PDZ domains are a recently characterized protein-recognition module. In mos t cases, PDZ domains bind to the C-terminal end of target proteins and are thought thereby to link these target proteins into functional signaling net works. We report the isolation of artificial PDZ domains selected via a mut agenesis screen in vivo, each recognizing a different C-terminal peptide. W e demonstrate that the PDZ domains isolated can bind selectively to their t arget peptides in vitro and in vivo. Two of the target peptides chosen are the C-terminal ends of two cellular transmembrane proteins with which no kn own PDZ domains have been reported to interact. By targeting these artifici al PDZ domains to the nucleus, interacting target peptides were efficiently transported to the same subcellular localization. One of the isolated PDZ domains was tested and shown to be efficiently directed to the plasma membr ane when cotransfected with the full-length transmembrane protein in mammal ian cells. Thus, artificial PDZ domains can be engineered and used to targe t intracellular proteins to different subcellular compartments.