Selection of proteins with desired properties from natural proteome libraries using mRNA display

mRNA display is a powerful yet challenging in vitro selection technique that can be used to identify proteins with desired properties from both natural proteome and combinatorial polypeptide libraries. The physical conjugation between a protein and its own RNA presents unique challenges in manipulating the displayed proteins at a low nanomolar scale in an RNase-free environment. The following protocol outlines the generation of cDNA libraries derived from natural organisms as well as the steps required for generation of mRNA-protein fusion molecules, in vitro functional selection and regeneration of the selected cDNA library. The selection procedures for the identification of protease substrates and Ca(2+)-dependent calmodulin-binding proteins from natural cDNA libraries are presented as examples. The method can be generally applied to the identification of protein sequences with desired properties from various natural proteome libraries. One round of mRNA display-based selection can be accomplished in ~7 d.