Måns Ehrenberg - Academia.edu (original) (raw)

Papers by Måns Ehrenberg

The EMBO Journal, 1996

We studied the dissociation rates of peptidyl-tRNA from the P-site of poly(U)-programmed wild-typ... more We studied the dissociation rates of peptidyl-tRNA from the P-site of poly(U)-programmed wild-type Escherichia coli ribosomes, hyperaccurate variants altered in S12 (SmD, SmP) and error-prone variants (Ram) altered in S4 or S5. The experiments were carried out in the presence and absence of streptomycin, and the effects of neomycin were tested in the wild-type ribosomes. Binding of peptidyl-tRNA to the P-site of wild-type ribosomes is much stronger than to their A-site. Addition of streptomycin dramatically reduces its affinity for the P-site. The S12 alterations make the P-site binding of peptidyl-tRNA much tighter, and the S4, S5 alterations make it weaker than in the case of the wild-type. We find that when binding of peptidyl-tRNA to the A-site is weak, then the affinity for the P-site is stronger, and vice versa. From these results, we formulate a hypothesis for the actions of streptomycin and neomycin based on deformations of the 16S rRNA tertiary structure. The results are also used to interpret some in vivo experiments on translational processivity.

Proceedings of the National Academy of Sciences, 2016

Significance Antibiotics are widely used to treat bacterial infections, but their mechanisms of a... more Significance Antibiotics are widely used to treat bacterial infections, but their mechanisms of action are often poorly understood. Viomycin is a tuberactinomycin antibiotic used for treating multidrug-resistant tuberculosis. Using an in vitro translation system that displays kinetic rates comparable to those in living cells we have characterized the mechanism of action of viomycin and constructed a kinetic model for how viomycin inhibits the translocation step of the peptide elongation cycle. Our results are vital for understanding the mechanism of the antimicrobial activity of viomycin and its sister drugs in living bacteria as well as resistance mechanisms against them, which can have strong implications for global health.

Journal of biology, 2005

During the translation of mRNA into polypeptide, elongation factor G (EF-G) catalyzes the translo... more During the translation of mRNA into polypeptide, elongation factor G (EF-G) catalyzes the translocation of peptidyl-tRNA from the A site to the P site of the ribosome. According to the 'classical' model, EF-G in the GTP-bound form promotes translocation, while hydrolysis of the bound GTP promotes dissociation of the factor from the post-translocation ribosome. According to a more recent model, EF-G operates like a 'motor protein' and drives translocation of the peptidyl-tRNA after GTP hydrolysis. In both the classical and motor protein models, GDP-to-GTP exchange is assumed to occur spontaneously on 'free' EF-G even in the absence of a guanine-nucleotide exchange factor (GEF). We have made a number of findings that challenge both models. First, free EF-G in the cell is likely to be in the GDP-bound form. Second, the ribosome acts as the GEF for EF-G. Third, after guanine-nucleotide exchange, EF-G in the GTP-bound form moves the tRNA2-mRNA complex to an interm...

RNA, 2014

There is evidence that tRNA bodies have evolved to reduce differences between aminoacyl-tRNAs in ... more There is evidence that tRNA bodies have evolved to reduce differences between aminoacyl-tRNAs in their affinity to EF-Tu. Here, we study the kinetics of incorporation of L-amino acids (AAs) Phe, Ala allyl-glycine (aG), methyl-serine (mS), and biotinyl-lysine (bK) using a tRNAAla-based body (tRNAAlaB) with a high affinity for EF-Tu. Results are compared with previous data on the kinetics of incorporation of the same AAs using a tRNAPheB body with a comparatively low affinity for EF-Tu. All incorporations exhibited fast and slow phases, reflecting the equilibrium fraction of AA-tRNA in active ternary complex with EF-Tu:GTP before the incorporation reaction. Increasing the concentration of EF-Tu increased the amplitude of the fast phase and left its rate unaltered. This allowed estimation of the affinity of each AA-tRNA to EF-Tu:GTP during translation, showing about a 10-fold higher EF-Tu affinity for AA-tRNAs formed from the tRNAAlaB body than from the tRNAPheB body. At ∼1 µM EF-Tu, t...

Molecular Cell, 2002

some in the absence of a class 1 RF, and its binding destabilizes that of RF1 or RF2. The formati... more some in the absence of a class 1 RF, and its binding destabilizes that of RF1 or RF2. The formation of RF3•GTP therefore leads to rapid dissociation of RF1 or RF2 from the ribosome. Subsequent hydrolysis of GTP on RF3 leads to its fast dissociation in the GDP confor

Current Opinion in Microbiology, 2008

Our understanding of the accuracy of tRNA selection on the messenger RNA programmed ribosome has ... more Our understanding of the accuracy of tRNA selection on the messenger RNA programmed ribosome has recently increased dramatically because of high-resolution crystal structures of the ribosome, cryo-electron microscopy reconstructions of its functional complexes, and fast kinetics experiments. Application of single-molecule spectroscopy with fluorescence resonance energy transfer to studies of tRNA selection by the ribosome has also provided new, albeit controversial, insights. Interestingly, when the fundamental trade-off between rate and accuracy in substrate-selective biosynthetic reactions is taken into account, some aspects of the current models of ribosome function appear strikingly suboptimal in the context of growing bacterial cells.

Proceedings of the National Academy of Sciences of the United States of America, Nov 29, 2016

Aminoacyl-tRNAs (aa-tRNAs) are selected by the messenger RNA programmed ribosome in ternary compl... more Aminoacyl-tRNAs (aa-tRNAs) are selected by the messenger RNA programmed ribosome in ternary complex with elongation factor Tu (EF-Tu) and GTP and then, again, in a proofreading step after GTP hydrolysis on EF-Tu. We use tRNA mutants with different affinities for EF-Tu to demonstrate that proofreading of aa-tRNAs occurs in two consecutive steps. First, aa-tRNAs in ternary complex with EF-Tu·GDP are selected in a step where the accuracy increases linearly with increasing aa-tRNA affinity to EF-Tu. Then, following dissociation of EF-Tu·GDP from the ribosome, the accuracy is further increased in a second and apparently EF-Tu-independent step. Our findings identify the molecular basis of proofreading in bacteria, highlight the pivotal role of EF-Tu for fast and accurate protein synthesis, and illustrate the importance of multistep substrate selection in intracellular processing of genetic information.

The Eclipse Time of Plasmid R1 may be due to structural processes and/or multiple step control.

Nucleic Acids Research, 2016

The antibiotic drug fusidic acid (FA) is commonly used in the clinic against gram-positive bacter... more The antibiotic drug fusidic acid (FA) is commonly used in the clinic against gram-positive bacterial infections. FA targets ribosome-bound elongation factor G (EF-G), a translational GTPase that accelerates both messenger RNA (mRNA) translocation and ribosome recycling. How FA inhibits translocation was recently clarified, but FA inhibition of ribosome recycling by EF-G and ribosome recycling factor (RRF) has remained obscure. Here we use fast kinetics techniques to estimate mean times of ribosome splitting and the stoichiometry of GTP hydrolysis by EF-G at varying concentrations of FA, EF-G and RRF. These mean times together with previous data on uninhibited ribosome recycling were used to clarify the mechanism of FA inhibition of ribosome splitting. The biochemical data on FA inhibition of translocation and recycling were used to model the growth inhibitory effect of FA on bacterial populations. We conclude that FA inhibition of translocation provides the dominant cause of bacterial growth reduction, but that FA inhibition of ribosome recycling may contribute significantly to FA-induced expression of short regulatory open reading frames, like those involved in FA resistance.

Proceedings of the National Academy of Sciences, 2010

We studied the pH-dependence of ribosome catalyzed peptidyl transfer from fMet-tRNA fMet to the a... more We studied the pH-dependence of ribosome catalyzed peptidyl transfer from fMet-tRNA fMet to the aa-tRNAs Phe-tRNA Phe , Ala-tRNA Ala , Gly-tRNA Gly , Pro-tRNA Pro , Asn-tRNA Asn , and Ile-tRNA Ile , selected to cover a large range of intrinsic pK a -values for the α-amino group of their amino acids. The peptidyl transfer rates were different at pH 7.5 and displayed different pH-dependence, quantified as the pH-value, , at which the rate was half maximal. The -values were downshifted relative to the intrinsic pK a -value of aa-tRNAs in bulk solution. Gly-tRNA Gly had the smallest downshift, while Ile-tRNA Ile and Ala-tRNA Ala had the largest downshifts. These downshifts correlate strongly with molecular dynamics (MD) estimates of the downshifts in pK a -values of these aa-tRNAs upon A-site binding. Our data show the chemistry of peptide bond formation to be rate limiting for peptidyl transfer at pH 7.5 in the Gly and Pro cases and indicate rate limiting chemistry for all six aa-tRNAs.

Physical Review Letters, 2000

Many intracellular components are present in low copy numbers per cell and subject to feedback co... more Many intracellular components are present in low copy numbers per cell and subject to feedback control. We use chemical master equations to analyze a negative feedback system where species X and S regulate each other's synthesis with standard intracellular kinetics. For a given number of X-molecules, S-variation can be significant. We show that this signal noise does not necessarily increase X-variation as previously thought but, surprisingly, can be necessary to reduce it below a Poissonian limit. The principle resembles Stochastic Resonance in that signal noise improves signal detection.

Journal of the American Chemical Society, 2012

Translations with unnatural amino acids (AAs) are generally inefficient and kinetic studies of th... more Translations with unnatural amino acids (AAs) are generally inefficient and kinetic studies of their incorporations from tRNAs are few. Here, the incorporations of small and large, non-N-alkylated, unnatural L-AAs into dipeptides were compared with natural amino acids using quench-flow techniques. Surprisingly, all incorporations occurred in two phases: fast then slow, and the incorporations of unnatural AA-tRNAs proceeded with rates of fast and slow phases similar to those for natural Phe-tRNA Phe. The slow phases were much more pronounced with unnatural AA-tRNAs, correlating with their known inefficient incorporations. Importantly, even for unnatural aa-tRNAs the fast phases could be made dominant by using high EF-Tu concentrations and/or lower reaction temperature, which may be generally useful for improving incorporations. Also, our observed effects of EF-Tu concentration on the fraction of the fast phase of incorporation enabled direct assay of the affinities of the AA-tRNAs for EF-Tu during translation. Our unmodified tRNA Phe derivative adaptor charged with a large unnatural AA, biotinyl-lysine, had a very low affinity for EF-Tu:GTP, while the small unnatural AAs on the same tRNA body had essentially the same affinities to EF-Tu:GTP as natural AAs on this tRNA, but still twofold less than natural Phe-tRNA Phe. We conclude that the inefficiencies of unnatural AA-tRNA incorporations were caused by inefficient delivery to the ribosome by EF-Tu, not slow peptide bond formation on the ribosome.

Journal of Structural Biology, 2004

A method of supervised classification using two available structure templates was applied to inve... more A method of supervised classification using two available structure templates was applied to investigate the possible heterogeneity existing in a large cryo-EM dataset of an Escherichia coli 70S ribosome-EF-G complex. Two subpopulations showing the ribosome in distinct conformational states, related by a ratchet-like rotation of the 30S subunit with respect to the 50S subunit, were extracted from the original dataset. The possible presence of additional intermediate states is discussed.

Philosophical Transactions of the Royal Society B: Biological Sciences, 2017

Two sets of ribosome structures have recently led to two different interpretations of what limits... more Two sets of ribosome structures have recently led to two different interpretations of what limits the accuracy of codon translation by transfer RNAs. In this review, inspired by this intermezzo at the Ribosome Club, we briefly discuss accuracy amplification by energy driven proofreading and its implementation in genetic code translation. We further discuss general ways by which the monitoring bases of 16S rRNA may enhance the ultimate accuracy ( d -values) and how the codon translation accuracy is reduced by the actions of Mg 2+ ions and the presence of error inducing aminoglycoside antibiotics. We demonstrate that complete freezing-in of cognate-like tautomeric states of ribosome-bound nucleotide bases in transfer RNA or messenger RNA is not compatible with recent experiments on initial codon selection by transfer RNA in ternary complex with elongation factor Tu and GTP. From these considerations, we suggest that the sets of 30S subunit structures from the Ramakrishnan group and 70...

Proceedings of the National Academy of Sciences, 2009

In translation, elongation factor Tu (EF-Tu) molecules deliver aminoacyl-tRNAs to the mRNA-progra... more In translation, elongation factor Tu (EF-Tu) molecules deliver aminoacyl-tRNAs to the mRNA-programmed ribosome. The GTPase activity of EF-Tu is triggered by ribosome-induced conformational changes of the factor that play a pivotal role in the selection of the cognate aminoacyl-tRNAs. We present a 6.7-Å cryo-electron microscopy map of the aminoacyl-tRNA·EF-Tu·GDP·kirromycin-bound Escherichia coli ribosome, together with an atomic model of the complex obtained through molecular dynamics flexible fitting. The model reveals the conformational changes in the conserved GTPase switch regions of EF-Tu that trigger hydrolysis of GTP, along with key interactions, including those between the sarcin-ricin loop and the P loop of EF-Tu, and between the effector loop of EF-Tu and a conserved region of the 16S rRNA. Our data suggest that GTP hydrolysis on EF-Tu is controlled through a hydrophobic gate mechanism.