Domain acquisition by class I aminoacyl-tRNA synthetase urzymes coordinated the catalytic functions of HVGH and KMSKS motifs.

Leucyl-tRNA synthetase (LeuRS) is a Class I aminoacyl-tRNA synthetase (aaRS) that synthesizes leucyl-tRNAleu for codon-directed protein synthesis. Two signature sequences, HxGH and KMSKS help stabilize transition-states for amino acid activation and tRNA aminoacylation by all Class I aaRS. Separate alanine mutants of each signature, together with the double mutant, behave in opposite ways in Pyrococcus horikoshii LeuRS and the 129-residue urzyme ancestral model generated from it (LeuAC). Free energy coupling terms, Δ(ΔG‡), for both reactions are large and favourable for LeuRS, but unfavourable for LeuAC. Single turnover assays with 32Pα-ATP show correspondingly different internal products. These results implicate domain motion in catalysis by full-length LeuRS. The distributed thermodynamic cycle of mutational changes authenticates LeuAC urzyme catalysis far more convincingly than do single point mutations. Most importantly, the evolutionary gain of function induced by acquiring the anticodon-binding (ABD) and multiple insertion modules in the catalytic domain appears to be to coordinate the catalytic function of the HxGH and KMSKS signature sequences. The implication that backbone elements of secondary structures achieve a major portion of the overall transition-state stabilization by LeuAC is also consistent with coevolution of the genetic code and metabolic pathways necessary to produce histidine and lysine sidechains.

Partitioning of the initial catalytic steps of leucyl-tRNA synthetase is driven by an active site peptide-plane flip.

To correctly aminoacylate tRNALeu, leucyl-tRNA synthetase (LeuRS) catalyzes three reactions: activation of leucine by ATP to form leucyl-adenylate (Leu-AMP), transfer of this amino acid to tRNALeu and post-transfer editing of any mischarged product. Although LeuRS has been well characterized biochemically, detailed structural information is currently only available for the latter two stages of catalysis. We have solved crystal structures for all enzymatic states of Neisseria gonorrhoeae LeuRS during Leu-AMP formation. These show a cycle of dramatic conformational changes, involving multiple domains, and correlate with an energetically unfavorable peptide-plane flip observed in the active site of the pre-transition state structure. Biochemical analyses, combined with mutant structural studies, reveal that this backbone distortion acts as a trigger, temporally compartmentalizing the first two catalytic steps. These results unveil the remarkable effect of this small structural alteration on the global dynamics and activity of the enzyme.

O-GlcNAc modification of leucyl-tRNA synthetase 1 integrates leucine and glucose availability to regulate mTORC1 and the metabolic fate of leucine.

All living organisms have the ability to sense nutrient levels to coordinate cellular metabolism. Despite the importance of nutrient-sensing pathways that detect the levels of amino acids and glucose, how the availability of these two types of nutrients is integrated is unclear. Here, we show that glucose availability regulates the central nutrient effector mTORC1 through intracellular leucine sensor leucyl-tRNA synthetase 1 (LARS1). Glucose starvation results in O-GlcNAcylation of LARS1 on residue S1042. This modification inhibits the interaction of LARS1 with RagD GTPase and reduces the affinity of LARS1 for leucine by promoting phosphorylation of its leucine-binding site by the autophagy-activating kinase ULK1, decreasing mTORC1 activity. The lack of LARS1 O-GlcNAcylation constitutively activates mTORC1, supporting its ability to sense leucine, and deregulates protein synthesis and leucine catabolism under glucose starvation. This work demonstrates that LARS1 integrates leucine and glucose availability to regulate mTORC1 and the metabolic fate of leucine.

A Leucyl-tRNA Synthetase Urzyme: Authenticity of tRNA Synthetase Catalytic Activities and Promiscuous Phosphorylation of Leucyl-5'AMP.

Aminoacyl-tRNA synthetase (aaRS)/tRNA cognate pairs translate the genetic code by synthesizing specific aminoacyl-tRNAs that are assembled on messenger RNA by the ribosome. Deconstruction of the two distinct aaRS superfamilies (Classes) has provided conceptual and experimental models for their early evolution. Urzymes, containing ~120-130 amino acids excerpted from regions where genetic coding sequence complementarities have been identified, are key experimental models motivated by the proposal of a single bidirectional ancestral gene. Previous reports that Class I and Class II urzymes accelerate both amino acid activation and tRNA aminoacylation have not been extended to other synthetases. We describe a third urzyme (LeuAC) prepared from the Class IA Pyrococcus horikoshii leucyl-tRNA synthetase. We adduce multiple lines of evidence for the authenticity of its catalysis of both canonical reactions, amino acid activation and tRNALeu aminoacylation. Mutation of the three active-site lysine residues to alanine causes significant, but modest reduction in both amino acid activation and aminoacylation. LeuAC also catalyzes production of ADP, a non-canonical enzymatic function that has been overlooked since it first was described for several full-length aaRS in the 1970s. Structural data suggest that the LeuAC active site accommodates two ATP conformations that are prominent in water but rarely seen bound to proteins, accounting for successive, in situ phosphorylation of the bound leucyl-5'AMP phosphate, accounting for ADP production. This unusual ATP consumption regenerates the transition state for amino acid activation and suggests, in turn, that in the absence of the editing and anticodon-binding domains, LeuAC releases leu-5'AMP unusually slowly, relative to the two phosphorylation reactions.

Leucyl-tRNA synthetase is a tumour suppressor in breast cancer and regulates codon-dependent translation dynamics.

Tumourigenesis and cancer progression require enhanced global protein translation1-3. Such enhanced translation is caused by oncogenic and tumour-suppressive events that drive the synthesis and activity of translational machinery4,5. Here we report the surprising observation that leucyl-tRNA synthetase (LARS) becomes repressed during mammary cell transformation and in human breast cancer. Monoallelic genetic deletion of LARS in mouse mammary glands enhanced breast cancer tumour formation and proliferation. LARS repression reduced the abundance of select leucine tRNA isoacceptors, leading to impaired leucine codon-dependent translation of growth suppressive genes, including epithelial membrane protein 3 (EMP3) and gamma-glutamyltransferase 5 (GGT5). Our findings uncover a tumour-suppressive tRNA synthetase and reveal that dynamic repression of a specific tRNA synthetase-along with its downstream cognate tRNAs-elicits a downstream codon-biased translational gene network response that enhances breast tumour formation and growth.

Improvement of substrate recognition in branched-chain aminoacyl-tRNA synthetases from Escherichia coli under conditions of pyrophosphate amplification.

Isoleucyl-tRNA synthetase (IleRS), leucyl-tRNA synthetase (LeuRS), and valyl-tRNA synthetase (ValRS) are enzymes that have potential for the determination of l-isoleucine, l-leucine, and l-valine in food products and plasma. However, the disadvantages of these enzymes are their specificity and sensitivity. Here, we examined the substrate specificity of IleRS, LeuRS, and ValRS under various conditions of pyrophosphate amplification to improve their specificity and sensitivity. The amount of pyrophosphate produced in IleRS, LeuRS, and ValRS reactions was amplified after the addition of excess adenosine-5'-triphosphate and magnesium ions, and was approximately 9-, 8-, and 7-fold higher, respectively, for each of the initial l-amino acid substrates (50 µM). However, in addition to their target amino acids, IleRS, LeuRS, and ValRS also reacted with l-valine, l-lysine, and l-threonine, respectively. This substrate misrecognition was overcome by making the reaction pH more acidic and by increasing the magnesium ion concentration. The pyrophosphate amplification in IleRS, LeuRS, and ValRS reactions resulted in the production of p1, p4-di (adenosine) 5'-tetraphosphate. We also observed a strong positive correlation (R = 0.99) between the amount of pyrophosphate produced and the initial concentration of l-amino acid with 5 and 50 µM l-isoleucine, l-leucine, and l-valine. Our results suggest that amino acid assays using IleRS, LeuRS, and ValRS are promising methods to accurately measure l-valine, l-isoleucine, and l-leucine in food products and plasma.

Tissue-specific alternative splicing separates the catalytic and cell signaling functions of human leucyl-tRNA synthetase.

The aminoacyl-tRNA synthetases are an ancient and ubiquitous component of all life. Many eukaryotic synthetases balance their essential function, preparing aminoacyl-tRNA for use in mRNA translation, with diverse roles in cell signaling. Herein, we use long-read sequencing to discover a leukocyte-specific exon skipping event in human leucyl-tRNA synthetase (LARS). We show that this highly expressed splice variant, LSV3, is regulated by serine-arginine-rich splicing factor 1 (SRSF1) in a cell-type-specific manner. LSV3 has a 71 amino acid deletion in the catalytic domain and lacks any tRNA leucylation activity in vitro. However, we demonstrate that this LARS splice variant retains its role as a leucine sensor and signal transducer for the proliferation-promoting mTOR kinase. This is despite the exon deletion in LSV3 including a portion of the previously mapped Vps34-binding domain used for one of two distinct pathways from LARS to mTOR. In conclusion, alternative splicing of LARS has separated the ancient catalytic activity of this housekeeping enzyme from its more recent evolutionary role in cell signaling, providing an opportunity for functional specificity in human immune cells.

Protocol for improving diffraction quality of leucyl-tRNA synthetase 1 with methylation and post-crystallization soaking and cooling in cryoprotectants.

Leucyl-tRNA synthetase 1 (LARS1) synthesizes Leu-tRNALeu for protein synthesis and plays an important role in mTORC1 activation by sensing intracellular leucine concentrations. Here, we describe a protocol for the purification, reductive methylation, binding affinity measurement by microscale thermophoresis, T i value measurement by Tycho, and post-crystallization soaking and cooling in cryoprotectants to improve crystallization of LARS1. Collectively, this allowed us to build the RagD binding domain, which was shown to be a dynamic region of LARS1 refractory to crystallization. For complete details on the use and execution of this protocol, please refer to Kim et al. (2021).

Leucyl-tRNA synthetase 1 is required for proliferation of TSC-null cells.

Uncontrolled cell proliferation associated with cancer depends on the functional abrogation of at least one of tumor suppressor. In response to nutrient cue, tuberous sclerosis complex (TSC) works as a tumor suppressor which inhibits cell growth via negative regulation of the mammalian target of rapamycin complex (mTORC1). However, the regulation mechanism of nutrient-dependent cell proliferation in TSC-null cells remains unclear. Here, we demonstrate that leucine is required for cell proliferation through the activation of leucyl-tRNA synthetase (LARS1)-mTORC1 pathway in TSC-null cells. Cell proliferation and survival were attenuated by LARS1 knock-down or inhibitors in TSC-null cells. In addition, either rapamycin or LARS1 inhibitors significantly decreased colony formation ability while their combined treatment drastically attenuated it. Taken together, we suggest that LARS1 inhibitors might considered as novel tools for the regression of tumor growth and proliferation in TSC-null tumor cells which regrow upon discontinuation of the mTORC1 inhibition.

Structure-based modification of pyrazolone derivatives to inhibit mTORC1 by targeting the leucyl-tRNA synthetase-RagD interaction.

The enzyme leucyl-tRNA synthetase (LRS) and the amino acid leucine regulate the mechanistic target of rapamycin (mTOR) signaling pathway. Leucine-dependent mTORC1 activation depends on GTPase activating protein events mediated by LRS. In a prior study, compound BC-LI-0186 was discovered and shown to interfere with the mTORC1 signaling pathway by inhibiting the LRS-RagD interaction. However, BC-LI-0186 exhibited poor solubility and was metabolized by human liver microsomes. In this study, in silico physicochemical properties and metabolite analysis of BC-LI-0186 are used to investigate the addition of functional groups to improve solubility and microsomal stability. In vitro experiments demonstrated that 7b and 8a had improved chemical properties while still maintaining inhibitory activity against mTORC1. The results suggest a new strategy for the discovery of novel drug candidates and the treatment of diverse mTORC1-related diseases.

tRNA-Dependent Import of a Transit Sequence-Less Aminoacyl-tRNA Synthetase (LeuRS2) into the Mitochondria of Arabidopsis.

Aminoacyl-tRNA synthetases (AaRS) charge tRNAs with amino acids for protein translation. In plants, cytoplasmic, mitochondrial, and chloroplast AaRS exist that are all coded for by nuclear genes and must be imported from the cytosol. In addition, only a few of the mitochondrial tRNAs needed for translation are encoded in mitochondrial DNA. Despite considerable progress made over the last few years, still little is known how the bulk of cytosolic AaRS and respective tRNAs are transported into mitochondria. Here, we report the identification of a protein complex that ties AaRS and tRNA import into the mitochondria of Arabidopsis thaliana. Using leucyl-tRNA synthetase 2 (LeuRS2) as a model for a mitochondrial signal peptide (MSP)-less precursor, a ≈30 kDa protein was identified that interacts with LeuRS2 during import. The protein identified is identical with a previously characterized mitochondrial protein designated HP30-2 (encoded by At3g49560) that contains a sterile alpha motif (SAM) similar to that found in RNA binding proteins. HP30-2 is part of a larger protein complex that contains with TIM22, TIM8, TIM9 and TIM10 four previously identified components of the translocase for MSP-less precursors. Lack of HP30-2 perturbed mitochondrial biogenesis and function and caused seedling lethality during greening, suggesting an essential role of HP30-2 in planta.

Leucine-sensing mechanism of leucyl-tRNA synthetase 1 for mTORC1 activation.

Leucyl-tRNA synthetase 1 (LARS1) mediates activation of leucine-dependent mechanistic target of rapamycin complex 1 (mTORC1) as well as ligation of leucine to its cognate tRNAs, yet its mechanism of leucine sensing is poorly understood. Here we describe leucine binding-induced conformational changes of LARS1. We determine different crystal structures of LARS1 complexed with leucine, ATP, and a reaction intermediate analog, leucyl-sulfamoyl-adenylate (Leu-AMS), and find two distinct functional states of LARS1 for mTORC1 activation. Upon leucine binding to the synthetic site, H251 and R517 in the connective polypeptide and 50FPYPY54 in the catalytic domain change the hydrogen bond network, leading to conformational change in the C-terminal domain, correlating with RagD association. Leucine binding to LARS1 is increased in the presence of ATP, further augmenting leucine-dependent interaction of LARS1 and RagD. Thus, this work unveils the structural basis for leucine-dependent long-range communication between the catalytic and RagD-binding domains of LARS1 for mTORC1 activation.

Design and synthesis of N-(3-sulfamoylphenyl)amides as Trypanosoma brucei leucyl-tRNA synthetase inhibitors.

The protozoan parasite Trypanosoma brucei (T. brucei) causes human African trypanosomiasis (HAT), which is a fatal and neglected disease in the tropic areas, and new treatments are urgently needed. Leucyl-tRNA synthetase (LeuRS) is an attractive target for the development of antimicrobial agents. In this work, starting from the hit compound thiourea ZCL539, we designed and synthesized a series of amides as effective T. brucei LeuRS (TbLeuRS) synthetic site inhibitors. The most potent compounds 74 and 91 showed IC50 of 0.24 and 0.25 µM, which were about 700-fold more potent than the starting hit compound. The structure-activity relationship was also discussed. These compounds provided a new scaffold and lead compounds for further development of antitrypanosomal agents.

Synthesis and structure-activity studies of novel anhydrohexitol-based Leucyl-tRNA synthetase inhibitors.

Leucyl-tRNA synthetase (LeuRS) is a clinically validated target for the development of antimicrobials. This enzyme catalyzes the formation of charged tRNALeu molecules, an essential substrate for protein translation. In the first step of catalysis LeuRS activates leucine using ATP, forming a leucyl-adenylate intermediate. Bi-substrate inhibitors that mimic this chemically labile phosphoanhydride-linked nucleoside have proven to be potent inhibitors of different members of the aminoacyl-tRNA synthetase family but, to date, they have demonstrated poor antibacterial activity. We synthesized a small series of 1,5-anhydrohexitol-based analogues coupled to a variety of triazoles and performed detailed structure-activity relationship studies with bacterial LeuRS. In an in vitro assay, Kiapp values in the nanomolar range were demonstrated. Inhibitory activity differences between the compounds revealed that the polarity and size of the triazole substituents affect binding. X-ray crystallographic studies of N. gonorrhoeae LeuRS in complex with all the inhibitors highlighted the crucial interactions defining their relative enzyme inhibitory activities. We further examined their in vitro antimicrobial properties by screening against several bacterial and yeast strains. While only weak antibacterial activity against M. tuberculosis was detected, the extensive structural data which were obtained could make these LeuRS inhibitors a suitable starting point towards further antibiotic development.

Nano-sized formazan analogues: Synthesis, structure elucidation, antimicrobial activity and docking study for COVID-19.

Three series of nanosized-formazan analogues were synthesized from the reaction of dithiazone with various types of α-haloketones (ester and acetyl substituted hydrazonoyl chlorides and phenacyl bromides) in sodium ethoxide solution. The structure and the crystal size of the new synthesized derivatives were assured based on the spectral analyses, XRD and SEM data. The antibacterial and antifungal activities were evaluated by agar diffusion technique. The results showed mild to moderate antibacterial activities and moderate to potent antifungal activities. Significant antifungal activities were observed for four derivatives 3a, 3d, 5a and 5g on the pathogenic fungal strains; Aspergillus flavus and Candida albicans with inhibition zone ranging from 16 to 20 mm. Molecular docking simulations of the synthesized compounds into leucyl-tRNA synthetase editing domain of Candida albicans suggested that most formazan analogues can fit deeply forming stable complexes in the active site. Furthermore, we utilized the docking approach to examine the potential of these compounds to inhibit SARS-CoV-2 3CLpro. The results were very promising verifying these formazan analogues as a hopeful antiviral agents.

Deciphering the interaction of benzoxaborole inhibitor AN2690 with connective polypeptide 1 (CP1) editing domain of Leishmania donovani leucyl-tRNA synthetase.

Leucyl-tRNA synthetases (LRS) catalyze the linkage of leucine with tRNALeu. A large insertion CP1 domain (Connective Polypeptide 1) in LRS is responsible for post-transfer editing of mis-charged aminoacyl-tRNAs. Here, we characterized the CP1 domain of Leishmania donovani, a protozoan parasite, and its role in editing activity and interaction with broad spectrum anti-fungal, AN2690. The deletion mutant of LRS, devoid of CP1 domain (LRS-CP1Δ) was constructed, followed by determination of its role in editing and aminoacylation. Binding of AN2690 and different amino acids with CP1 deletion mutant and full length LRS was evaluated using isothermal titration calorimetry (ITC) and molecular dynamics simulations. The recombinant LRS-CP1Δ protein did not catalyze the aminoacylation and the editing reaction when compared to full-length LRS. Thus, indicating that CP1 domain was imperative for both aminoacylation and editing activities of LRS. Binding studies with different amino acids indicated selectivity of isoleucine by CP1 domain over other amino acids. These studies also indicated high affinity of AN2690 with the editing domain. Molecular docking studies indicated that AN2690-CP1 domain complex was stabilized by hydrogen bonding and hydrophobic interactions resulting in high binding affinity between the two. Our data suggests CP1 is crucial for the function of L.donovani LRS.

Molecular basis of the multifaceted functions of human leucyl-tRNA synthetase in protein synthesis and beyond.

Human cytosolic leucyl-tRNA synthetase (hcLRS) is an essential and multifunctional enzyme. Its canonical function is to catalyze the covalent ligation of leucine to tRNALeu, and it may also hydrolyze mischarged tRNAs through an editing mechanism. Together with eight other aminoacyl-tRNA synthetases (AaRSs) and three auxiliary proteins, it forms a large multi-synthetase complex (MSC). Beyond its role in translation, hcLRS has an important moonlight function as a leucine sensor in the rapamycin complex 1 (mTORC1) pathway. Since this pathway is active in cancer development, hcLRS is a potential target for anti-tumor drug development. Moreover, LRS from pathogenic microbes are proven drug targets for developing antibiotics, which however should not inhibit hcLRS. Here we present the crystal structure of hcLRS at a 2.5 Å resolution, the first complete structure of a eukaryotic LRS, and analyze the binding of various compounds that target different sites of hcLRS. We also deduce the assembly mechanism of hcLRS into the MSC through reconstitution of the entire mega complex in vitro. Overall, our study provides the molecular basis for understanding both the multifaceted functions of hcLRS and for drug development targeting these functions.

Synthesis, Characterization, and Biological Evaluation of Novel 7-Oxo-7H-thiazolo[3,2-b]-1,2,4-triazine-2-carboxylic Acid Derivatives.

A series of novel 7-oxo-7H-thiazolo[3,2-b]-1,2,4-triazine-2-carboxylic acid derivatives was synthesized in good yields by a multi-step procedure that included the generation of the S-alkylated derivatives from 6-substituted arylmethyl-3-mercapto-1,2,4-triazin-5-ones with ethyl 2-chloroacetoacetate, intramolecular cyclization with microwave irradiation, hydrolysis and amidation. All of the target compounds were fully characterized through 1H-NMR, 13C-NMR and HRMS spectra. The intramolecular cyclization occurred regioselectively at the N2-position of 1,2,4-triazine ring, which was confirmed by compound 3e using single-crystal X-ray diffraction analysis. The antibacterial and antitubercular activities of the target compounds were evaluated. Compared with Ciprofloxacin and Rifampicin, compounds 5d, 5f and 5g containing the terminal amide fragment exhibited broad spectrum antibacterial activity, and carboxylic acid derivatives or its corresponding ethyl esters had less effect on antibacterial properties. The most potent compound 5f also displayed excellent in vitro antitubercular activity against Mycobacterium smegmatis (minimum inhibitory concentration (MIC) = 50 µg/mL) and better growth inhibition activity of leucyl-tRNA synthetase (78.24 ± 4.05% at 15 µg/mL).

Duplication of leucyl-tRNA synthetase in an archaeal extremophile may play a role in adaptation to variable environmental conditions.

Aminoacyl-tRNA synthetases (aaRSs) are ancient enzymes that play a fundamental role in protein synthesis. They catalyze the esterification of specific amino acids to the 3'-end of their cognate tRNAs and therefore play a pivotal role in protein synthesis. Although previous studies suggest that aaRS-dependent errors in protein synthesis can be beneficial to some microbial species, evidence that reduced aaRS fidelity can be adaptive is limited. Using bioinformatics analyses, we identified two distinct leucyl-tRNA synthetase (LeuRS) genes within all genomes of the archaeal family Sulfolobaceae. Remarkably, one copy, designated LeuRS-I, had key amino acid substitutions within its editing domain that would be expected to disrupt hydrolytic editing of mischarged tRNALeu and to result in variation within the proteome of these extremophiles. We found that another copy, LeuRS-F, contains canonical active sites for aminoacylation and editing. Biochemical and genetic analyses of the paralogs within Sulfolobus islandicus supported the hypothesis that LeuRS-F, but not LeuRS-I, functions as an essential tRNA synthetase that accurately charges leucine to tRNALeu for protein translation. Although LeuRS-I was not essential, its expression clearly supported optimal S. islandicus growth. We conclude that LeuRS-I may have evolved to confer a selective advantage under the extreme and fluctuating environmental conditions characteristic of the volcanic hot springs in which these archaeal extremophiles reside.