Chemistry Department, Skidmore College, Saratoga Springs, New York, USA.
IUBMB Life. 2024 Aug;76(8):505-522. doi: 10.1002/iub.2811. Epub 2024 Feb 23.
The amide proteogenic amino acids, asparagine and glutamine, are two of the twenty amino acids used in translation by all known life. The aminoacyl-tRNA synthetases for asparagine and glutamine, asparaginyl-tRNA synthetase and glutaminyl tRNA synthetase, evolved after the split in the last universal common ancestor of modern organisms. Before that split, life used two-step indirect pathways to synthesize asparagine and glutamine on their cognate tRNAs to form the aminoacyl-tRNA used in translation. These two-step pathways were retained throughout much of the bacterial and archaeal domains of life and eukaryotic organelles. The indirect routes use non-discriminating aminoacyl-tRNA synthetases (non-discriminating aspartyl-tRNA synthetase and non-discriminating glutamyl-tRNA synthetase) to misaminoacylate the tRNA. The misaminoacylated tRNA formed is then transamidated into the amide aminoacyl-tRNA used in protein synthesis by tRNA-dependent amidotransferases (GatCAB and GatDE). The enzymes and tRNAs involved assemble into complexes known as transamidosomes to help maintain translational fidelity. These pathways have evolved to meet the varied cellular needs across a diverse set of organisms, leading to significant variation. In certain bacteria, the indirect pathways may provide a means to adapt to cellular stress by reducing the fidelity of protein synthesis. The retention of these indirect pathways versus acquisition of asparaginyl-tRNA synthetase and glutaminyl tRNA synthetase in lineages likely involves a complex interplay of the competing uses of glutamine and asparagine beyond translation, energetic costs, co-evolution between enzymes and tRNA, and involvement in stress response that await further investigation.
酰胺生成氨基酸天冬酰胺和谷氨酰胺是所有已知生命翻译过程中使用的二十种氨基酸中的两种。天冬酰胺酰-tRNA 合成酶和谷氨酰胺酰-tRNA 合成酶,是在现代生物最后共同祖先分歧之后进化而来的。在此之前,生命使用两步间接途径在其对应的 tRNA 上合成天冬酰胺和谷氨酰胺,以形成用于翻译的氨酰-tRNA。这些两步途径在细菌和古菌域的大部分生命和真核细胞器中都保留下来。间接途径使用非特异性氨酰-tRNA 合成酶(非特异性天冬氨酸-tRNA 合成酶和非特异性谷氨酰胺-tRNA 合成酶)错误氨酰化 tRNA。形成的错误氨酰化 tRNA 然后被 tRNA 依赖性氨酰转移酶(GatCAB 和 GatDE)转酰胺化为用于蛋白质合成的酰胺氨酰-tRNA。涉及的酶和 tRNA 组装成称为转酰胺体的复合物,以帮助维持翻译保真度。这些途径已经进化以满足各种生物体多样化的细胞需求,导致了显著的变异。在某些细菌中,间接途径可能通过降低蛋白质合成的保真度来提供适应细胞应激的手段。这些间接途径的保留与天冬酰胺酰-tRNA 合成酶和谷氨酰胺酰-tRNA 合成酶在谱系中的获得之间的关系可能涉及到除翻译之外,谷氨酰胺和天冬酰胺的竞争用途、酶和 tRNA 之间的共同进化、以及参与应激反应等复杂的相互作用,这些都有待进一步研究。