Two conformations of a crystalline human tRNA synthetase–tRNA complex: implications for protein synthesis

Aminoacylation of tRNA is the first step of protein synthesis. Here, we report the co-crystal structure of human tryptophanyl-tRNA synthetase and tRNA(Trp). This enzyme is reported to interact directly with elongation factor 1α, which carries charged tRNA to the ribosome. Crystals were generated from a 50/50% mixture of charged and uncharged tRNA(Trp). These crystals captured two conformations of the complex, which are nearly identical with respect to the protein and a bound tryptophan. They are distinguished by the way tRNA is bound. In one, uncharged tRNA is bound across the dimer, with anticodon and acceptor stem interacting with separate subunits. In this cross-dimer tRNA complex, the class I enzyme has a class II-like tRNA binding mode. This structure accounts for biochemical investigations of human TrpRS, including species-specific charging. In the other conformation, presumptive aminoacylated tRNA is bound only by the anticodon, the acceptor stem being free and having space to interact precisely with EF-1α, suggesting that the product of aminoacylation can be directly handed off to EF-1α for the next step of protein synthesis

The KMT2A recombinome of acute leukemias in 2023

Chromosomal rearrangements of the human KMT2A/MLL gene are associated with de novo as well as therapy-induced infant, pediatric, and adult acute leukemias. Here, we present the data obtained from 3401 acute leukemia patients that have been analyzed between 2003 and 2022. Genomic breakpoints within the KMT2A gene and the involved translocation partner genes (TPGs) and KMT2A-partial tandem duplications (PTDs) were determined. Including the published data from the literature, a total of 107 in-frame KMT2A gene fusions have been identified so far. Further 16 rearrangements were out-of-frame fusions, 18 patients had no partner gene fused to 5'-KMT2A, two patients had a 5'-KMT2A deletion, and one ETV6::RUNX1 patient had an KMT2A insertion at the breakpoint. The seven most frequent TPGs and PTDs account for more than 90% of all recombinations of the KMT2A, 37 occur recurrently and 63 were identified so far only once. This study provides a comprehensive analysis of the KMT2A recombinome in acute leukemia patients. Besides the scientific gain of information, genomic breakpoint sequences of these patients were used to monitor minimal residual disease (MRD). Thus, this work may be directly translated from the bench to the bedside of patients and meet the clinical needs to improve patient survival