title: Design of a bacterial host for site-specific incorporation of p-bromophenylalanine into recombinant proteins.
abstract: Introduction of a yeast suppressor tRNA (ytRNA(Phe)(CUA)) and a mutant yeast phenylalanyl-tRNA synthetase (yPheRS (T415G)) into an Escherichia coli expression host allows in vivo incorporation of phenylalanine analogues into recombinant proteins in response to amber stop codons. However, high-fidelity incorporation of non-natural amino acids is precluded in this system by mischarging of ytRNA(Phe)(CUA) with tryptophan (Trp) and lysine (Lys). Here we show that ytRNA(Phe)(CUA) and yPheRS can be redesigned to achieve high-fidelity amber codon suppression through delivery of p-bromophenylalanine (pBrF). Two strategies were used to reduce misincorporation of Trp and Lys. First, Lys misincorporation was eliminated by disruption of a Watson-Crick base pair between nucleotides 30 and 40 in ytRNA(Phe)(CUA). Loss of this base pair reduces mischarging by the E. coli lysyl-tRNA synthetase. Second, the binding site of yPheRS was redesigned to enhance specificity for pBrF. Specifically, we used the T415A variant, which exhibits 5-fold higher activity toward pBrF as compared to Trp in ATP-PP(i) exchange assays. Combining mutant ytRNA(Phe)(CUA) and yPheRS (T415A) allowed incorporation of pBrF into murine dihydrofolate reductase in response to an amber codon with at least 98% fidelity.
authors.affiliation: Division of Chemistry and Chemical Engineering, California Institute of Technology, 1200 East California Boulevard, Pasadena, California 91125, USA.
authors.forename: Inchan
authors.initials: I
authors.lastname: Kwon
authors.forename: Pin
authors.initials: P
authors.lastname: Wang
authors.forename: David A
authors.initials: DA
authors.lastname: Tirrell
mesh_terms: D000215:Acylation; D000255:Adenosine Triphosphate / Q000378:metabolism; D001665:Binding Sites; D018388:Codon, Terminator; D004926:Escherichia coli / Q000201:enzymology / Q000235:genetics* / Q000378:metabolism; D008239:Lysine / Q000235:genetics / Q000378:metabolism; D008250:Lysine-tRNA Ligase / Q000235:genetics* / Q000378:metabolism; D010649:Phenylalanine / Q000031:analogs & derivatives* / Q000235:genetics / Q000378:metabolism; D010957:Plasmids / Q000235:genetics; D012360:RNA, Transfer, Phe / Q000235:genetics* / Q000378:metabolism; D011994:Recombinant Proteins / Q000096:biosynthesis* / Q000235:genetics; D014364:Tryptophan / Q000235:genetics / Q000378:metabolism
chemical_list: D018388:Codon, Terminator; D012360:RNA, Transfer, Phe; D011994:Recombinant Proteins; C060302:4-bromophenylalanine; D010649:Phenylalanine; D014364:Tryptophan; D000255:Adenosine Triphosphate; D008250:Lysine-tRNA Ligase; D008239:Lysine