Targeting tRNA-synthetase interactions towards novel therapeutic discovery against eukaryotic pathogens.

The development of chemotherapies against eukaryotic pathogens is especially challenging because of both the evolutionary conservation of drug targets between host and parasite, and the evolution of strain-dependent drug resistance. There is a strong need for new nontoxic drugs with broad-spectrum activity against trypanosome parasites such as Leishmania and Trypanosoma. A relatively untested approach is to target macromolecular interactions in parasites rather than small molecular interactions, under the hypothesis that the features specifying macromolecular interactions diverge more rapidly through coevolution. We computed tRNA Class-Informative Features in humans and independently in eight distinct clades of trypanosomes, identifying parasite-specific informative features, including base pairs and base mis-pairs, that are broadly conserved over approximately 250 million years of trypanosome evolution. Validating these observations, we demonstrated biochemically that tRNA:aminoacyl-tRNA synthetase (aaRS) interactions are a promising target for anti-trypanosomal drug discovery. From a marine natural products extract library, we identified several fractions with inhibitory activity toward Leishmania major alanyl-tRNA synthetase (AlaRS) but no activity against the human homolog. These marine natural products extracts showed cross-reactivity towards Trypanosoma cruzi AlaRS indicating the broad-spectrum potential of our network predictions. We also identified Leishmania major threonyl-tRNA synthetase (ThrRS) inhibitors from the same library. We discuss why chemotherapies targeting multiple aaRSs should be less prone to the evolution of resistance than monotherapeutic or synergistic combination chemotherapies targeting only one aaRS.

Role of D-aminoacyl-tRNA deacylase beyond chiral proofreading as a cellular defense against glycine mischarging by AlaRS.

Strict L-chiral rejection through Gly-cisPro motif during chiral proofreading underlies the inability of D-aminoacyl-tRNA deacylase (DTD) to discriminate between D-amino acids and achiral glycine. The consequent Gly-tRNAGly 'misediting paradox' is resolved by EF-Tu in the cell. Here, we show that DTD's active site architecture can efficiently edit mischarged Gly-tRNAAla species four orders of magnitude more efficiently than even AlaRS, the only ubiquitous cellular checkpoint known for clearing the error. Also, DTD knockout in AlaRS editing-defective background causes pronounced toxicity in Escherichia coli even at low-glycine levels which is alleviated by alanine supplementation. We further demonstrate that DTD positively selects the universally invariant tRNAAla-specific G3•U70. Moreover, DTD's activity on non-cognate Gly-tRNAAla is conserved across all bacteria and eukaryotes, suggesting DTD's key cellular role as a glycine deacylator. Our study thus reveals a hitherto unknown function of DTD in cracking the universal mechanistic dilemma encountered by AlaRS, and its physiological importance.

Characterization of aminoacyl-tRNA synthetase stability and substrate interaction by differential scanning fluorimetry.

Differential scanning fluorimetry (DSF) is a fluorescence-based assay to evaluate protein stability by determining protein melting temperatures. Here, we describe the application of DSF to investigate aminoacyl-tRNA synthetase (AARS) stability and interaction with ligands. Employing three bacterial AARS enzymes as model systems, methods are presented here for the use of DSF to measure the apparent temperatures at which AARSs undergo melting transitions, and the effect of AARS substrates and inhibitors. One important observation is that the extent of temperature stability realized by an AARS in response to a particular bound ligand cannot be predicted a priori. The DSF method thus serves as a rapid and highly quantitative approach to measure AARS stability, and the ability of ligands to influence the temperature at which unfolding transitions occur.

Clinical manifestations of anti-synthetase syndrome positive for anti-alanyl-tRNA synthetase (anti-PL12) antibodies: a retrospective study of 17 cases.

OBJECTIVE: To describe the clinical manifestations of the anti-synthetase syndrome (ASS) specifically associated with anti-alanyl-tRNA (anti-PL12) synthetase antibodies. METHODS: In a retrospective study, 17 patients (eight males, nine females, mean age = 60.3 years) with ASS symptoms confirmed by two consecutive tests (cyto-dot and/or immunoblot, or both), with positive results for anti-PL12 antibodies, were included. RESULTS: All patients presented with interstitial lung disease (ILD), which was associated with mild myositis in 41% of the cases. RP and general impairment were common, whereas rheumatic and dermatological symptoms were uncommon. Four patients suffered from SS, and four others had an atypical oesophageal involvement. The long-term course was assessable for 10 patients (follow-up of 41.1 months). Five patients required immunosuppressive drugs. Two patients are waiting for a lung transplant because of disproportionate and refractory pulmonary hypertension. CONCLUSION: The severity of anti-PL12 ASS varied because of the constant pulmonary involvement. ILD was the predominant prognosis factor, which was notable in cases associated with pulmonary hypertension.

Autoantibodies against alanyl-tRNA synthetase and tRNAAla coexist and are associated with myositis.

The sera of six patients with autoimmune disease, predominantly myositis with pulmonary fibrosis, contain antibodies of the PL-12 specificity. These autoantibodies react with both protein and RNA components of human cells. The protein has a subunit molecular mass of 110 kD, and the RNA comprises a group of bands in the tRNA size class. Aminoacylation experiments identify the antigens as alanyl-tRNA synthetase and its corresponding tRNAs, tRNAAla. Anti-tRNA antibody can be absorbed out without depleting antisynthetase activity, showing that the antigens are recognized independently by separable antibodies that coexist in these sera. The concurrence of separate antibodies to the two components suggests that the autoimmune response may be mounted against the charging enzyme-tRNA complex. However, the antisynthetase antibody fails to coprecipitate tRNA with the enzyme, suggesting that the antibody reacts with its target only when it is not complexed with tRNA.

Reactions of the sulfhydryl groups of alanyl-tRNA Synthetase.

The six sulfhydryl groups in each subunit of the alanyl-tRNA synthetase of Escherichia coli react with sulfhydryl reagents with at least four different rates. One reacts very rapidly with 5,5'-dithiobis-(2-nitrobenzoic acid) (DTNB), and a second reacts somewhat less rapidly with this reagent. These two groups are required for transfer activity, which is lost in proportion to the extent of derivatization. Two other groups react more slowly, with a consequent loss of exchange activity. The remaining two sulfhydryl groups do not react with DTNB until the protein is denatured. The inactivations are reversed by dithiothreitol. Two sulfhydryl groups react with N-ethylmaleimide (NEM) and with a spin-label derivative of NEM. These reactions resemble the modification of two sulfhydryl groups with DTNB, in that they also inactivate the transfer reaction but not the ATP:PPi exchange. The two spin labels are incorporated at similar rates but are in very different environments, one highly exposed and one highly immobilized. These groups do not interact with Mn2+, which is bound to the enzyme in the absence of ATP.