18 research outputs found
Plant tumour biocontrol agent employs a tRNA-dependent mechanism to inhibit leucyl-tRNA synthetase
Leucyl-tRNA synthetases (LeuRSs) have an essential role in translation and are promising targets for antibiotic development. Agrocin 84 is a LeuRS inhibitor produced by the biocontrol agent Agrobacterium radiobacter K84 that targets pathogenic strains of A. tumefaciens, the causative agent of plant tumours. Agrocin 84 acts as a molecular Trojan horse and is processed inside the pathogen into a toxic moiety (TM84). Here we show using crystal structure, thermodynamic and kinetic analyses, that this natural antibiotic employs a unique and previously undescribed mechanism to inhibit LeuRS. TM84 requires tRNALeu for tight binding to the LeuRS synthetic active site, unlike any previously reported inhibitors. TM84 traps the enzymeâtRNA complex in a novel âaminoacylation-likeâ conformation, forming novel interactions with the KMSKS loop and the tRNA 30-end. Our findings reveal an intriguing tRNAdependent inhibition mechanism that may confer a distinct evolutionary advantage in vivo and inform future rational antibiotic design
Folding studies of the #beta#-sheet protein pseudoazurin
SIGLEAvailable from British Library Document Supply Centre-DSC:D201441 / BLDSC - British Library Document Supply CentreGBUnited Kingdo
A partially folded intermediate species of the ÎČ-sheet protein apo-pseudoazurin ism trapped during proline-limited folding
The folding of apo-pseudoazurin, a 123-residue, predominantly -sheet protein with a complex Greek key topology, has been investigated using several biophysical techniques. Kinetic analysis of refolding using farand near-ultraviolet circular dichroism (UV CD) shows that the protein folds slowly to the native state with rate constants of 0.04 and 0.03 minâ1, respectively, at pH 7.0 and at 15°C. This process has an activation enthalpy of âŒ90 kJ/mole and is catalyzed by cyclophilin A, indicating that folding is limited by trans-cis proline isomerization, presumably around the Xaa-Pro 20 bond that is in the cis isomer in the native state. Before proline isomerization, an intermediate accumulates during folding. This species has a substantial signal in the far-UV CD, a nonnative signal in the near-UV CD, exposed hydrophobic surfaces (judged by 1-anilino naphthalenesulphonate binding), a noncooperative denaturation transition, and a dynamic structure (revealed by line broadening on the nuclear magnetic resonance time scale). We compare the properties of this intermediate with partially folded states of other proteins and discuss its role in folding of this complex Greek key protein
The Transpolar Drift as a Source of Riverine and ShelfâDerived Trace Elements to the Central Arctic Ocean
A major surface circulation feature of the Arctic Ocean is the Transpolar Drift (TPD), a current that transports riverâinfluenced shelf water from the Laptev and East Siberian Seas toward the center of the basin and Fram Strait. In 2015, the international GEOTRACES program included a highâresolution panâArctic survey of carbon, nutrients, and a suite of trace elements and isotopes (TEIs). The cruises bisected the TPD at two locations in the central basin, which were defined by maxima in meteoric water and dissolved organic carbon concentrations that spanned 600 km horizontally and ~25â50 m vertically. Dissolved TEIs such as Fe, Co, Ni, Cu, Hg, Nd, and Th, which are generally particleâreactive but can be complexed by organic matter, were observed at concentrations much higher than expected for the openocean setting. Other trace element concentrations such as Al, V, Ga, and Pb were lower than expected due to scavenging over the productive East Siberian and Laptev shelf seas. Using a combination of radionuclide tracers and ice drift modeling, the transport rate for the core of the TPD was estimated at 0.9 ± 0.4 Sv(106m3 sâ1). This rate was used to derive the mass flux for TEIs that were enriched in the TPD, revealing the importance of lateral transport in supplying materials beneath the ice to the central Arctic Ocean and potentially to the North Atlantic Ocean via Fram Strait. Continued intensification of the Arctic hydrologicc ycle and permafrost degradation will likely lead to an increase in the flux of TEIs into the Arctic Ocean