Structural states of the flexible catalytic loop of M. tuberculosis tyrosyl-tRNA synthetase in different enzyme-substrate complexes.

Tyrosyl-tRNA synthetase from Mycobacterium tuberculosis (MtTyrRS) is an enzyme that belongs to class I of aminoacyl-tRNA synthetases, which catalyze the attachment of L-tyrosine to its cognate tRNATyr in the preribosomal step of protein synthesis. MtTyrRS is incapable of cross-recognition and aminoacylation of human cytoplasmic tRNATyr, so this enzyme may be a promising target for development of novel selective inhibitors as putative antituberculosis drugs. As a class I aminoacyl-tRNA synthetase, MtTyrRS contains the HIGH-like and KFGKS catalytic motifs that catalyze amino acid activation with ATP. In this study, the conformational mobility of MtTyrRS catalytic KFGKS loop was analyzed by 100-ns all-atoms molecular dynamics simulations of the free enzyme and its complexes with different substrates: tyrosine, ATP, and the tyrosyl-adenylate intermediate. It was shown that in the closed state of the active site, the KFGKS loop, readily adopts different stable conformations depending on the type of bound substrate. Molecular dynamics simulations revealed that the closed state of the loop is stabilized by dynamic formation of two antiparallel ß-sheets at flanking ends which hold the KFGKS fragment inside the active center. Prevention of ß-sheet formation by introducing point mutations in the loop sequence results in a rapid (<20 ns) transition of the loop from its functional "closed" M-like structure to an inactive "open" O-like structure, i.e. rapid diffusion of the catalytic loop outside the active site. The flexibility and rapid dynamics of the wild-type aaRS catalytic loop structure are crucial for formation of protein-substrate interactions and subsequently for overall enzyme functional activity.

Asymmetric structure and domain binding interfaces of human tyrosyl-tRNA synthetase studied by molecular dynamics simulations.

Human tyrosyl-tRNA synthetase (HsTyrRS) is composed of two structural modules: N-terminal catalytic core and an EMAP II-like C-terminal domain. The structures of these modules are known, but no crystal structure of the full-length HsTyrRS is currently available. An all-atom model of the full-length HsTyrRS was developed in this work. The structure, dynamics, and domain binding interfaces of HsTyrRS were investigated by extensive molecular dynamics (MD) simulations. Our data suggest that HsTyrRS in solution consists of a number of compact asymmetric conformations, which differ significantly by their rigidity, internal mobility, orientation of C-terminal modules, and the strength of interdomain binding. Interfaces of domain binding obtained in MD simulations are in perfect agreement with our previous coarse-grained hierarchical rotations technique simulations. Formation of the hydrogen bonds between R93 residue of the ELR cytokine motif and the residues A340 and E479 in the C-module was observed. This observation supports the idea that the lack of cytokine activity in the full-length HsTyrRS is explained by interactions between N-modules and C-modules, which block the ELR motif.

Computational modeling and molecular dynamics simulations of mammalian cytoplasmic tyrosyl-tRNA synthetase and its complexes with substrates.

Cytoplasmic tyrosyl-tRNA synthetase (TyrRS) is one of the key enzymes of protein biosynthesis. TyrRSs of pathogenic organisms have gained attention as potential targets for drug development. Identifying structural differences between various TyrRSs will facilitate the development of specific inhibitors for the TyrRSs of pathogenic organisms. However, there is a deficiency in structural data for mammalian cytoplasmic TyrRS in complexes with substrates. In this work, we constructed spatial structure of full-length Bos taurus TyrRS (BtTyrRS) and its complexes with substrates using the set of computational modeling techniques. Special attention was paid to BtTyrRS complexes with substrates [L-tyrosine, K+ and ATP:Mg2+] and intermediate products [tyrosyl-adenylate (Tyr-AMP), K+ and PPi:Mg2+] with the different catalytic loop conformations. In order to analyze their dynamical properties, we performed 100 ns of molecular dynamics (MD) simulations. MD simulations revealed new structural data concerning the tyrosine activation reaction in mammalian TyrRS. Formation of strong interaction between Lys154 and γ-phosphate suggests the additional role of CP1 insertion as an important factor for ATP binding. The presence of a potassium-binding pocket within the active site of mammalian TyrRS compensates the absence of the second lysine in the KMSKS motif. Our data provide new details concerning a role of K+ ions at different stages of the first step of the tyrosylation reaction, including the coordination of substrates and involvement in the PPi releasing. The results of this work suggest that differences between ATP-binding sites of mammalian and bacterial TyrRSs are meaningful and could be exploited in the drug design.

Cytokine-like activities of some aminoacyl-tRNA synthetases and auxiliary p43 cofactor of aminoacylation reaction and their role in oncogenesis.

Multifunctionality of proteins is among mechanisms accounting for the complexity of interactome networks in higher eukaryotes. During oncogenesis and other pathologic conditions many proteins perform additional functions without changes in three dimensional structures. One family of these moonlighting proteins is represented by enzymes and cofactors of aminoacylation reactions, by means of which tRNAs are attached to their cognate amino acids. Tyrosyl-tRNA synthetase (TyrRS), tryptophanyl-tRNA synthetases (TrpRS) and auxiliary factor of mammalian multi-aminoacyl-tRNA synthetases, p43 (precusor of endothelial monocyte activating polypeptide II - EMAP II) upon their release in intracellular environment become proinflammatory cytokines with multiple activities during apoptosis, angiogenesis and inflammation. In addition, these proteins play important role in cancer progression, modulating tumor angiogenesis and its escape from surveillance by immune system.