Dual Routes for S. aureus Asparaginyl‐tRNA Formation

Abstract

Two routes have evolved for attaching the amino acid asparagine (Asn) to its correct transfer RNA (tRNAAsn), an essential step in protein synthesis. The direct pathway involves aminoacylation of tRNAAsn by asparaginyl‐tRNA synthetase (AsnRS) when free Asn is available. In the indirect pathway, a non‐discriminating aspartyl‐tRNA snthetase (ND‐AspRS) attaches Asp to tRNAAsn, and the tRNA‐bound Asp is then amidated to Asn by GatCAB. Bioinformatics suggests the human pathogen Staphylococccus aureus may encode the indirect pathway in addition to the direct one. We set out to determine if, S. aureus does in fact encode an ND‐AspRS and GatCAB for tRNA‐dependent Asn synthesis. Using the E. coli JF448 system, we demonstrate that the concerted activities of S. aureus AspRS and GatCAB can form Asn on tRNA. In addition, using the E. coli TrpA34 system, we are verifying the S. aureus AspRS enzyme is non‐discriminating supported by in vitro studies with the enzyme. We speculate encoding dual routes for Asn‐tRNAAsn formation enables S. aureus to take advantage of situations when Asn is plentiful.