Transforming a Pair of Orthogonal tRNA-aminoacyl-tRNA Synthetase from Archaea to Function in Mammalian Cells

A previously engineered Methanocaldococcus jannaschii –tyrosyl-tRNA synthetase pair orthogonal to Escherichia coli was modified to become orthogonal in mammalian cells. The resulting -tyrosyl-tRNA synthetase pair was able to suppress an amber codon in the green fluorescent protein, GFP, and in a foldon protein in mammalian cells. The methodology reported here will allow rapid transformation of the much larger collection of existing tyrosyl-tRNA synthetases that were already evolved for the incorporation of an array of over 50 unnatural amino acids into proteins in Escherichia coli into proteins in mammalian cells. Thus we will be able to introduce a large array of possibilities for protein modifications in mammalian cells

Emerging biotechnology to detect weak and/or transient protein-protein interactions

textProtein-protein interactions are of great importance to a number of essential biological processes including cell cycle regulation, cell-cell interactions, DNA replication, transcription and translation. Thus, an understanding of protein-protein interactions is critical for understanding many facets of cell function. Unfortunately, the tools and methods currently in use to identify and study protein-protein interactions focus largely on high affinity, stable interactions. However, the majority of the protein-protein interactions involved in regulatory processes have weak affinities and are transient in nature. Therefore, it is important to develop new biotechnology capable of detecting weak and/or transient protein-protein interactions in vivo. Here, we describe four new methods that allow for the identification and study of weak and/or transient protein-protein interactions in vivo. First, we developed a rapid method to convert Escherichia coli orthogonal tRNA/synthetase pairs into an orthogonal system for mammalian cells in order to site-specifically incorporate unnatural amino acids into any gene of interest using stop codon suppression. This method will allow the expression and purification of proteins that carry normally transient post-translational modifications. Second, we successfully employed site-specific unnatural amino acid incorporation to chemically cross-link a known homodimer, Sortase A, in vivo. Third, we developed a novel tetracycline repressor-based mammalian two-hybrid system and successfully detected homo- and hetero-dimers that are known to have weak binding constants. Finally, a synthetic antibody (termed a synbody) that binds weakly to the SH3 domain of the proto-oncogene Abelson tyrosine kinase was developed. The synbody can potentially be used as a first generation drug and/or biomarker. We hope that the methods developed in this dissertation will enable the scientific community to better understand weak/transient protein-protein interactions in vivo.Pharmac

Suppression of an amber codon inserted into the GFP-encoding gene.

<p>(A) Full-length GFP was expressed in HEK 293T cells only in the presence of a <i>M. jannaschii</i> TyrRS- pair designed to be orthogonal to mammalian cells. (B) Western blot analysis of full-length GFP probed with anti-His antibodies.</p

The orthogonality of the <i>M. jannaschii</i> TyrRS- pair was verified on western blots probed with anti-V5 antibodies.

<p>Expression of full-length foldon was monitored when various tRNAs were introduced into the HEK 293T cells. Note that the tRNA mutants used in these experiments were slightly different from those depicted in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0011263#pone-0011263-g001" target="_blank">figure 1</a>.</p