In Vivo Incorporation of Unnatural Amino Acids into Proteins
Final rept. 1 Mar 2001-28 Feb 2002
SCRIPPS RESEARCH INST LA JOLLA CA
Pagination or Media Count:
A method for the site-specific incorporation of unnatural amino acids into proteins in vivo would significantly facilitate studies of the cellular function of proteins, as well as make possible the biosynthesis of unnatural polymers and proteins with novel structures and activities. Our approach consists of the generation of amber suppressor tRNAaminoacyl-tRNA synthetase pair that are not catalytically competent with all the endogenous Escherichia coli tRNAs an aminoacyl-tRNA synthetases, followed by directed evolution of such orthogonal aminoacyl-tRNA synthetases to alter their amino acid specificities. A new orthogonal suppressor tRNAaminoacyl-tRNA synthetase pair in E. coli has been derived from the Saccharomyces cerevisiae tRNA sub Asp and aspartyl-tRNA syathetase, and the in vitro and in vivo characteristics of this pair were determined. In order to achieve a high specificity for the amino acid, a direct selection for site-specific incorporation of unnatural amino acids into a reporter epitope displayed on the surface of M13 phage has been developed and characterized. Under simulated selection conditions, phage particles displaying aspartate were enriched over 300-fold from a pool of phage displaying asparagine using monoclonal antibodies raised against the aspartate-containing epitope. The direct phage selection offers very high specificity for the amino acid of interest, Which cannot be achieved by conventional methods.