A tRNA-independent Mechanism for Transamidosome Assembly Promotes Aminoacyl-tRNA Transamidation

Many bacteria lack genes encoding asparaginyl- and/or glutaminyl-tRNA synthetase and consequently rely on an indirect path for the synthesis of both Asn-tRNA Asn and Gln-tRNA Gln . In some bacteria such as Thermus thermophilus , efficient delivery of misacylated tRNA to the downstream amidotransferase (AdT) is ensured by formation of a stable, tRNA-dependent macromolecular complex called the Asn-transamidosome. This complex enables direct delivery of Asp-tRNA Asn from the non-discriminating aspartyl-tRNA synthetase to AdT, where it is converted into Asn-tRNA Asn . Previous characterization of the analogous Helicobacter pylori Asn-transamidosome revealed that it is dynamic and cannot be stably isolated, suggesting the possibility of an alternative mechanism to facilitate assembly of a stable complex. We have identified a novel protein partner called Hp0100 as a component of a stable, tRNA-independent H. pylori Asn-transamidosome; this complex contains a non-discriminating aspartyl-tRNA synthetase, AdT, and Hp0100 but does not require tRNA Asn for assembly. Hp0100 also enhances the capacity of AdT to convert Asp-tRNA Asn into Asn-tRNA Asn by ∼35-fold. Our results demonstrate that bacteria have adopted multiple divergent methods for transamidosome assembly and function. Background: Some microorganisms use indirect tRNA aminoacylation to produce Asn-tRNA Asn ; the necessary components are assembled into a tRNA Asn -dependent transamidosome complex. Results: A new protein, Hp0100, facilitates formation of an alternative, tRNA-independent transamidosome and increases the efficiency of Asp-tRNA Asn transamidation. Conclusion: Hp0100 is a component of a stable efficient Helicobacter pylori transamidosome. Significance: The Hp0100-containing transamidosome allows for optimal indirect biosynthesis of Asn-tRNA Asn .