Carbohydrate recognition is essential for growth, cell adhesion and signalling in all living organisms. A highly conserved carbohydrate binding module, LysM, is found in proteins from viruses, ...bacteria, fungi, plants and mammals. LysM modules recognize polysaccharides containing N-acetylglucosamine (GlcNAc) residues including peptidoglycan, an essential component of the bacterial cell wall. However, the molecular mechanism underpinning LysM-peptidoglycan interactions remains unclear. Here we describe the molecular basis for peptidoglycan recognition by a multimodular LysM domain from AtlA, an autolysin involved in cell division in the opportunistic bacterial pathogen Enterococcus faecalis. We explore the contribution of individual modules to the binding, identify the peptidoglycan motif recognized, determine the structures of free and bound modules and reveal the residues involved in binding. Our results suggest that peptide stems modulate LysM binding to peptidoglycan. Using these results, we reveal how the LysM module recognizes the GlcNAc-X-GlcNAc motif present in polysaccharides across kingdoms.
The Heliconius butterflies are a diverse recent radiation comprising multiple levels of divergence with ongoing gene flow between species. The recently sequenced genome of Heliconius melpomene ...allowed us to investigate the genomic evolution of this group using dense RAD marker sequencing. Phylogenetic analysis of 54 individuals robustly supported reciprocal monophyly of H. melpomene and Heliconius cydno and refuted previous phylogenetic hypotheses that H. melpomene may be paraphylectic with respect to H. cydno. Heliconius timareta also formed a monophyletic clade closely related but distinct from H. cydno with Heliconius heurippa falling within this clade. We find evidence for genetic admixture between sympatric populations of the sister clades H. melpomene and H. cydno/timareta, particularly between H. cydno and H. melpomene from Central America and between H. timareta and H. melpomene from the eastern slopes of the Andes. Between races, divergence is primarily explained by isolation by distance and there is no detectable genetic population structure between parapatric races, suggesting that hybrid zones between races are not zones of secondary contact. Our results also support previous findings that colour pattern loci are shared between populations and species with similar colour pattern elements. Furthermore, this pattern is almost unique to these genomic regions, with only a very small number of other loci showing significant similarity between populations and species with similar colour patterns.
Coupling of fast protein dynamics to enzyme chemistry is controversial and has ignited considerable debate, especially over the past 15 years in relation to enzyme-catalyzed H-transfer. H-transfer ...can occur by quantum tunneling, and the temperature dependence of kinetic isotope effects (KIEs) has emerged as the “gold standard” descriptor of these reactions. The anomalous temperature dependence of KIEs is often rationalized by invoking fast motions to facilitate H-transfer, yet crucially, direct evidence for coupled motions is lacking. The fast motions hypothesis underpinning the temperature dependence of KIEs is based on inference. Here, we have perturbed vibrational motions in pentaerythritol tetranitrate reductase (PETNR) by isotopic substitution where all non-exchangeable atoms were replaced with the corresponding heavy isotope (13C, 15N, and 2H). The KIE temperature dependence is perturbed by heavy isotope labeling, demonstrating a direct link between (promoting) vibrations in the protein and the observed KIE. Further we show that temperature-independent KIEs do not necessarily rule out a role for fast dynamics coupled to reaction chemistry. We show causality between fast motions and enzyme chemistry and demonstrate how this impacts on experimental KIEs for enzyme reactions.
Nuclear magnetic resonance (NMR) is a powerful tool to study three‐dimensional structures as well as protein conformational fluctuations in solution, but it is compromised by increases in peak widths ...and missing signals. We previously reported that ubiquitin has two folded conformations, N1 and N2 and plus another folded conformation, I, in which some amide group signals of residues 33–41 almost disappeared above 3 kbar at pH 4.5 and 273 K. Thus, well‐converged structural models could not be obtained for this region owing to the absence of distance restraints. Here, we reexamine the problem using the ubiquitin Q41N variant as a model for this locally disordered conformation, I. We demonstrate that the variant shows pressure‐induced loss of backbone amide group signals at residues 28, 33, 36, and 39–41 like the wild‐type, with a similar but smaller effect on CαH and CβH signals. In order to characterize this I structure, we measured paramagnetic relaxation enhancement (PRE) under high pressure to obtain distance restraints, and calculated the structure assisted by Bayesian inference. We conclude that the more disordered I conformation observed at pH 4.0, 278 K, and 2.5 kbar largely retained the N2 conformation, although the amide groups at residues 33–41 have more heterogeneous conformations and more contact with water, which differ from the N1 and N2 states. The PRE‐assisted strategy has the potential to improve structural characterization of proteins that lack NMR signals, especially for relatively more open and hydrated protein conformations.
Heliconius butterflies represent a recent radiation of species, in which wing pattern divergence has been implicated in speciation. Several loci that control wing pattern phenotypes have been mapped ...and two were identified through sequencing. These same gene regions play a role in adaptation across the whole Heliconius radiation. Previous studies of population genetic patterns at these regions have sequenced small amplicons. Here, we use targeted next-generation sequence capture to survey patterns of divergence across these entire regions in divergent geographical races and species of Heliconius. This technique was successful both within and between species for obtaining high coverage of almost all coding regions and sufficient coverage of non-coding regions to perform population genetic analyses. We find major peaks of elevated population differentiation between races across hybrid zones, which indicate regions under strong divergent selection. These ‘islands’ of divergence appear to be more extensive between closely related species, but there is less clear evidence for such islands between more distantly related species at two further points along the ‘speciation continuum’. We also sequence fosmid clones across these regions in different Heliconius melpomene races. We find no major structural rearrangements but many relatively large (greater than 1 kb) insertion/deletion events (including gain/loss of transposable elements) that are variable between races.
Enzyme regulation is vital for metabolic adaptability in living systems. Fine control of enzyme activity is often delivered through post-translational mechanisms, such as allostery or allokairy. ...β-phosphoglucomutase (βPGM) from Lactococcus lactis is a phosphoryl transfer enzyme required for complete catabolism of trehalose and maltose, through the isomerisation of β-glucose 1-phosphate to glucose 6-phosphate via β-glucose 1,6-bisphosphate. Surprisingly for a gatekeeper of glycolysis, no fine control mechanism of βPGM has yet been reported. Herein, we describe allomorphy, a post-translational control mechanism of enzyme activity. In βPGM, isomerisation of the K145-P146 peptide bond results in the population of two conformers that have different activities owing to repositioning of the K145 sidechain. In vivo phosphorylating agents, such as fructose 1,6-bisphosphate, generate phosphorylated forms of both conformers, leading to a lag phase in activity until the more active phosphorylated conformer dominates. In contrast, the reaction intermediate β-glucose 1,6-bisphosphate, whose concentration depends on the β-glucose 1-phosphate concentration, couples the conformational switch and the phosphorylation step, resulting in the rapid generation of the more active phosphorylated conformer. In enabling different behaviours for different allomorphic activators, allomorphy allows an organism to maximise its responsiveness to environmental changes while minimising the diversion of valuable metabolites.
Talin mediates attachment of the cell to the extracellular matrix. It is targeted by the Rap1 effector RIAM to focal adhesion sites and subsequently undergoes force-induced conformational opening to ...recruit the actin-interacting protein vinculin. The conformational switch involves the talin R3 domain, which binds RIAM when closed and vinculin when open. Here, we apply pressure to R3 and measure 1H, 15N, and 13C chemical shift changes, which are fitted using a simple model, and indicate that R3 is only 50% closed: the closed form is a four-helix bundle, while in the open state helix 1 is twisted out. Strikingly, a mutant of R3 that binds RIAM with an affinity similar to wild-type but more weakly to vinculin is shown to be 0.84 kJ mol−1 more stable when closed. These results demonstrate that R3 is thermodynamically poised to bind either RIAM or vinculin, and thus constitutes a good mechanosensitive switch.
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•An analysis of pressure-dependent data reveals chemical shifts of both states•The open state is 50% populated and has helix 1 opened out•Implies a stepwise opening of the 4-helix bundle in response to tension•Shows talin is thermodynamically poised for opening as a mechanosensitive switch
Baxter et al. used high pressure to increase the population of the open state of the R3 domain of talin. They calculated chemical shifts of closed and open states, showing that the open state has helix 1 opened out, representing the start of force-dependent opening.
Wing patterning in Heliconius butterflies is a longstanding example of both Müllerian mimicry and phenotypic radiation under strong natural selection. The loci controlling such patterns are ..."hotspots" for adaptive evolution with great allelic diversity across different species in the genus. We characterise nucleotide variation, genotype-by-phenotype associations, linkage disequilibrium, and candidate gene expression at two loci and across multiple hybrid zones in Heliconius melpomene and relatives. Alleles at HmB control the presence or absence of the red forewing band, while alleles at HmYb control the yellow hindwing bar. Across HmYb two regions, separated by approximately 100 kb, show significant genotype-by-phenotype associations that are replicated across independent hybrid zones. In contrast, at HmB a single peak of association indicates the likely position of functional sites at three genes, encoding a kinesin, a G-protein coupled receptor, and an mRNA splicing factor. At both HmYb and HmB there is evidence for enhanced linkage disequilibrium (LD) between associated sites separated by up to 14 kb, suggesting that multiple sites are under selection. However, there was no evidence for reduced variation or deviations from neutrality that might indicate a recent selective sweep, consistent with these alleles being relatively old. Of the three genes showing an association with the HmB locus, the kinesin shows differences in wing disc expression between races that are replicated in the co-mimic, Heliconius erato, providing striking evidence for parallel changes in gene expression between Müllerian co-mimics. Wing patterning loci in Heliconius melpomene therefore show a haplotype structure maintained by selection, but no evidence for a recent selective sweep. The complex genetic pattern contrasts with the simple genetic basis of many adaptive traits studied previously, but may provide a better model for most adaptation in natural populations that has arisen over millions rather than tens of years.
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Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
β-Phosphoglucomutase (βPGM) catalyzes isomerization of β- d -glucose 1-phosphate (βG1P) into d -glucose 6-phosphate (G6P) via sequential phosphoryl transfer steps using a β- d -glucose ...1,6-bisphosphate (βG16BP) intermediate. Synthetic fluoromethylenephosphonate and methylenephosphonate analogs of βG1P deliver novel step 1 transition state analog (TSA) complexes for βPGM, incorporating trifluoromagnesate and tetrafluoroaluminate surrogates of the phosphoryl group. Within an invariant protein conformation, the β- d -glucopyranose ring in the βG1P TSA complexes (step 1) is flipped over and shifted relative to the G6P TSA complexes (step 2). Its equatorial hydroxyl groups are hydrogen-bonded directly to the enzyme rather than indirectly via water molecules as in step 2. The (C)O–P bond orientation for binding the phosphate in the inert phosphate site differs by ∼30° between steps 1 and 2. By contrast, the orientations for the axial O–Mg–O alignment for the TSA of the phosphoryl group in the catalytic site differ by only ∼5°, and the atoms representing the five phosphorus-bonded oxygens in the two transition states (TSs) are virtually superimposable. The conformation of βG16BP in step 1 does not fit into the same invariant active site for step 2 by simple positional interchange of the phosphates: the TS alignment is achieved by conformational change of the hexose rather than the protein.
Objective To investigate the effectiveness of facilitated physical activity as an adjunctive treatment for adults with depression presenting in primary care.Design Pragmatic, multicentre, two arm ...parallel randomised controlled trial.Setting General practices in Bristol and Exeter.Participants 361 adults aged 18-69 who had recently consulted their general practitioner with symptoms of depression. All those randomised had a diagnosis of an episode of depression as assessed by the clinical interview schedule-revised and a Beck depression inventory score of 14 or more.Interventions In addition to usual care, intervention participants were offered up to three face to face sessions and 10 telephone calls with a trained physical activity facilitator over eight months. The intervention was based on theory and aimed to provide individually tailored support and encouragement to engage in physical activity.Main outcome measures The primary outcome was self reported symptoms of depression, assessed with the Beck depression inventory at four months post-randomisation. Secondary outcomes included use of antidepressants and physical activity at the four, eight, and 12 month follow-up points, and symptoms of depression at eight and 12 month follow-up.Results There was no evidence that participants offered the physical activity intervention reported improvement in mood by the four month follow-up point compared with those in the usual care group; adjusted between group difference in mean Beck depression inventory score −0.54 (95% confidence interval −3.06 to 1.99; P=0.68). Similarly, there was no evidence that the intervention group reported a change in mood by the eight and 12 month follow-up points. Nor was there evidence that the intervention reduced antidepressant use compared with usual care (adjusted odds ratio 0.63, 95% confidence interval 0.19 to 2.06; P=0.44) over the duration of the trial. However, participants allocated to the intervention group reported more physical activity during the follow-up period than those allocated to the usual care group (adjusted odds ratio 2.27, 95% confidence interval 1.32 to 3.89; P=0.003).Conclusions The addition of a facilitated physical activity intervention to usual care did not improve depression outcome or reduce use of antidepressants compared with usual care alone.Trial registration Current Controlled Trials ISRCTN16900744.
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