Preferential Association Research Articles

Two Arabidopsis Chloroplast GrpE Homologues Exhibit Distinct Biological Activities and Can Form Homo- and Hetero-Oligomers.

Flowering plants have evolved two distinct clades of chloroplast GrpE homologues (CGEs), which are the nucleotide exchange factor for Hsp70. In Arabidopsis, they are named AtCGE1 (At5g17710) and AtCGE2 (At1g36390). Characterization of their corresponding T-DNA insertion mutants revealed that there is no visible change in phenotype except a defect in protein import in an AtCGE2-knockout mutant under normal growth conditions. However, the embryo development of an AtCGE1-knockout mutant was arrested early at the globular stage. An AtCGE1-knockdown mutant, harboring a T-DNA insertion in the 5′-UTR region, exhibited growth retardation and protein import defect, and its mutant phenotypes became more severe when AtCGE2 was further knocked out. Sub-organellar distribution implied that AtCGE2 might be important for membrane biology due to its preferential association with chloroplast membranes. Biochemical studies and complementation tests showed that only AtCGE1, but not AtCGE2, can effectively rescue the heat-sensitive phenotype of Escherichia coli grpE mutant and robustly stimulate the refolding of denatured luciferase by DnaK. Interestingly, AtCGE1 and AtCGE2 are tending to form heterocomplexes, which exhibit comparable co-chaperone activity to AtCGE1 homocomplexes. Our data indicate that AtCGE1 is the principle functional homologue of GrpE. The possibility that AtCGE2 has a subsidiary or regulatory function through homo- and/or hetero-oligomerization is discussed.

Activation-induced substrate engagement in ERK signaling.

The extracellular signal-regulated kinase (ERK) pathway is an essential component of developmental signaling in metazoans. Previous models of pathway activation suggested that dissociation of activated dually phosphorylated ERK (dpERK) from MAPK/ERK kinase (MEK), a kinase that phosphorylates ERK, and other cytoplasmic anchors, is sufficient for allowing ERK interactions with its substrates. Here, we provide evidence for an additional step controlling ERK’s access to substrates. Specifically, we demonstrate that interaction of ERK with its substrate Capicua (Cic) is controlled at the level of ERK phosphorylation, whereby Cic binds to dpERK much stronger than to unphosphorylated ERK, both in vitro and in vivo. Mathematical modeling suggests that the differential affinity of Cic for dpERK versus ERK is required for both down-regulation of Cic and stabilizing phosphorylated ERK. Preferential association of Cic with dpERK serves two functions: it prevents unproductive competition of Cic with unphosphorylated ERK and contributes to efficient signal propagation. We propose that high-affinity substrate binding increases the specificity and efficiency of signal transduction through the ERK pathway.

Unique cellular interaction of macrophage-targeted liposomes potentiates anti-inflammatory activity.

Nanomedicines that suppress macrophage-mediated chronic inflammation are important therapeutics for many inflammatory diseases. The small-sized (<100 nm) apoptotic-cell-mimetic macrophage-targeted liposomes served as a long-lasting immunosuppressive agent through preferential association with CD300a receptor, unlike larger liposomes, enabling the amelioration of hepatic inflammation in mice.

A quantitative ex vivo study of the interactions between reconstituted high-density lipoproteins and human leukocytes.

Knowledge of the interactions between nanoparticles and immune cells is required for optimal design of nanoparticle-based drug delivery systems, either when aiming to avoid phagocytic clearance of the nanoparticles or promote an immune response by delivering therapeutic agents to specific immune cells. Several studies have suggested that reconstituted high-density lipoproteins (rHDL) are attractive drug delivery vehicles. However, detailed studies of rHDL interactions with circulating leukocytes are limited. Here, we evaluated the association of discoidal rHDL with leukocytes in human whole blood (HWB) using quantitative approaches. We found that while the rHDL of various lipid compositions associated preferentially with monocytes, the degree of association depended on the lipid composition. However, consistent with the long circulation half-life of rHDL, we show that only a minor fraction of the rHDL associated with the leukocytes. Furthermore, we used three-dimensional fluorescence microscopy and imaging flow cytometry to evaluate the possible internalization of rHDL cargo into the cells, and we show increased internalization of rHDL cargo in monocytes relative to granulocytes. The preferential rHDL association with monocytes and the internalization of rHDL cargo could possibly be mediated by the scavenger receptor class B type 1 (SR-BI), which we show is expressed to a higher extent on monocytes than on the other major leukocyte populations. Our work implies that drug-loaded rHDL can deliver its cargo to monocytes in circulation, which could lead to some off-target effects when using rHDL for systemic drug delivery, or it could pave the way for novel immunotherapeutic treatments aiming to target the monocytes.

Inter-Arm Blood Pressure Difference in Diabetes Mellitus and Its Preferential Association with Peripheral Artery Disease.

Aim: Inter-arm blood pressure difference (IAD) is known to be associated with a composite of cardiovascular disease (CVD) and with CVD risk factors. However, only limited information is available regarding the contribution of diabetes mellitus to IAD and the association of IAD with individual CVDs, such as coronary artery disease (CAD), stroke, and peripheral artery disease (PAD).Methods: We addressed these issues in this cross-sectional study of 2580 participants who had simultaneous blood pressure measurements in both arms using an automated device.Results: Compared with 1,264 nondiabetic subjects, 1316 patients with diabetes mellitus had a greater IAD (P = 0.01) and a higher prevalence of IAD of ≥ 10 mmHg (8.4% vs. 5.4%, P = 0.002). However, such difference was not significant after the adjustment for potential confounders. Among CAD, stroke, and PAD, only PAD was significantly associated with IAD in a model adjusted for the CVD risk factors. Age was found to modify the association between IAD and PAD, with the association being more prominent in the younger subgroup.Conclusion: Thus, diabetes mellitus itself was not an independent factor associated with IAD. A larger IAD was preferentially associated with the presence of PAD, and this association was modified by age.

Social structure of Atlantic spotted dolphins (Stenella frontalis) off Bimini, The Bahamas (2003–2016): alternate reasons for preferential association in delphinids

Social systems are characterized by the associations and interactions between individuals. For highly social groups such as delphinids, understanding the demographics and long-term association patterns of a population is the first step in interpreting its overall social structure and specific relationships between individuals. This study investigated the social patterns of a population of Atlantic spotted dolphins (Stenella frontalis) off Bimini, The Bahamas, during a 14-year period (2003–2016). We generated association indices and conducted cluster, network, and temporal analyses using SOCPROG 2.8. Dolphins in this population display long-term, year-round residency around Bimini, as well as long-term preferences in association with a combination of rapid disassociation, constant companions, and casual acquaintances. We found no evidence of distinct social clusters within the study group; however, we discovered at least one subgroup with higher association than the rest of the population. This group was composed of male spotted dolphins, which overall tended to associate together more than females and chose companions with similar levels of association to themselves. Despite strong relationships between males, we found no evidence for the existence of alliances or coalitions. This study provides a baseline understanding of the social structure of this population that will allow us to investigate the variable relationships between individuals, in addition to exploring the effects of demographic changes within the resident population.

Topological analysis of the gp41 MPER on lipid bilayers relevant to the metastable HIV-1 envelope prefusion state

The membrane proximal external region (MPER) of HIV-1 envelope glycoprotein (gp) 41 is an attractive vaccine target for elicitation of broadly neutralizing antibodies (bNAbs) by vaccination. However, current details regarding the quaternary structural organization of the MPER within the native prefusion trimer [(gp120/41)3] are elusive and even contradictory, hindering rational MPER immunogen design. To better understand the structural topology of the MPER on the lipid bilayer, the adjacent transmembrane domain (TMD) was appended (MPER-TMD) and studied. Membrane insertion of the MPER-TMD was sensitive both to the TMD sequence and cytoplasmic residues. Antigen binding of MPER-specific bNAbs, in particular 10E8 and DH511.2_K3, was significantly impacted by the presence of the TMD. Furthermore, MPER-TMD assembly into 10-nm diameter nanodiscs revealed a heterogeneous membrane array comprised largely of monomers and dimers, as enumerated by bNAb Fab binding using single-particle electron microscopy analysis, arguing against preferential trimeric association of native MPER and TMD protein segments. Moreover, introduction of isoleucine mutations in the C-terminal heptad repeat to induce an extended MPER α-helical bundle structure yielded an antigenicity profile of cell surface-arrayed Env variants inconsistent with that found in the native prefusion state. In line with these observations, electron paramagnetic resonance analysis suggested that 10E8 inhibits viral membrane fusion by lifting the MPER N-terminal region out of the viral membrane, mandating the exposure of residues that would be occluded by MPER trimerization. Collectively, our data suggest that the MPER is not a stable trimer, but rather a dynamic segment adapted for structural changes accompanying fusion.

Skin-Deep Surface Patterning of Calcite

The influence of soluble additives on the growth of calcite (CaCO3) is usually rationalized based on changes in crystal morphologies, where preferential association of the additives with either the acute or obtuse steps on the crystal surface gives rise to specific growth forms. In this work we investigate the influence of a highly acidic organic additive with calcite, cp20k from the barnacle Megabalanus rosa, and demonstrate that in addition to modifying the crystal morphology, additives can be used to generate calcite crystals with different surface architectures. These can potentially rise to interesting optical effects that may be important in applications such as in coatings and paints. These surface features form during dissolution/reprecipitation at the crystal surface during the incubation of crystals in solution, and confocal fluorescence microscopy confirmed they are limited to the surface of the crystal only. The surface patterning can also be tuned using alternative additives, mixtures of additives and by varying the solution conditions. Notably, we also show that surface structures can be used to determine the mode of interaction of additives with the microscopic surface steps under conditions where only minor changes in morphology have occurred. Introduction.

Tryptase values in anaphylaxis and insect allergy.

To recognize the relevance of serum tryptase measurement as a useful tool for the diagnosis of allergic diseases and mast cell disorders. Recent data on the role of mast cells and tryptase in allergic and other diseases provide new understanding into the mechanisms and causes of anaphylaxis. Measurement of transiently elevated tryptase levels shortly after a severe reaction can help elucidate mechanism behind the reaction in identifying mast cell activation. Hymenoptera venom allergy represents an important cause of morbidity and mortality worldwide. Venom allergy is a typical IgE-mediated reaction because of sensitization to one or more allergens of the venom, and accounts for 1.5-34% of all cases of anaphylaxis. There is a preferential association between insect venom allergy and mastocytosis. The diagnosis of a clonal mast cell disease leads to therapeutic consequences concerning the treatment of venom allergy. In conclusion, baseline tryptase levels support the clinical diagnosis of anaphylaxis and mast cell disorders, determine venom immunotherapy treatment and are relevant in deciding on lifelong treatment.

Group I metabotropic glutamate receptors in the primate motor thalamus: subsynaptic association with cortical and sub-cortical glutamatergic afferents.

Preclinical evidence indicates that mGluR5 is a potential therapeutic target for Parkinson's disease and L-DOPA-induced dyskinesia. However, the mechanisms through which these therapeutic benefits are mediated remain poorly understood. Although the regulatory role of mGluR5 on glutamatergic transmission has been examined in various basal ganglia nuclei, very little is known about the localization and function of mGluR5 in the ventral motor and intralaminar thalamic nuclei, the main targets of basal ganglia output in mammals. Thus, we used immuno-electron microscopy to map the cellular and subcellular localization of group I mGluRs (mGluR1a and mGluR5) in the ventral motor and caudal intralaminar thalamic nuclei in rhesus monkeys. Furthermore, using double immuno-electron microscopy, we examined the subsynaptic localization of mGluR5 in relation to cortical and sub-cortical glutamatergic afferents. Four major conclusions can be drawn from these data. First, mGluR1a and mGluR5 are expressed postsynaptically on the plasma membrane of dendrites of projection neurons and GABAergic interneurons in the basal ganglia- and cerebellar-receiving regions of the ventral motor thalamus and in CM. Second, the plasma membrane-bound mGluR5 immunoreactivity is preferentially expressed perisynaptically at the edges of cortical and sub-cortical glutamatergic afferents. Third, the mGluR5 immunoreactivity is more strongly expressed in the lateral than the medial tiers of CM, suggesting a preferential association with thalamocortical over thalamostriatal neurons in the primate CM. Overall, mGluR5 is located to subserve powerful modulatory role of cortical and subcortical glutamatergic transmission in the primate ventral motor thalamus and CM.

Comparative analysis of habitat use and ontogenetic habitat-shifts among coral reef damselfishes

Habitat characteristics play an important role in determining the structure of fish communities. The decline in fish diversity and abundance with the decline in coral diversity and cover may be explained by habitat specialisation and partitioning among reef fishes and/or preferences for particular corals that are susceptible to disturbance. These preferences may develop at different life history stages. Here, we investigated patterns of habitat specialisation and ontogenetic shifts in habitat preference among 14 co-existing damselfish species at Lizard Island lagoon on the Great Barrier Reef. Although live coral cover contributed only 26% of the substratum, 28% of adults and 57% of new settlers were mostly found on live coral, indicating a strong preference for live coral habitat by new settlers. Only a few species exhibited a high degree of habitat specialisation and low overlap in habitat use with other species. Specialisation differed among species and life stages. New settlers were more commonly associated with finely branched corymbose corals and using those habitats with higher frequency than expected based on habitat availability alone. Adults were more commonly linked to more open branching morphologies or non-coral substrata. Our results suggest that habitat loss may not uniformly impact on all life stages. While adult individuals may not be as reliant as juveniles on corals, detrimental effects of habitat loss on juvenile survival may have longer-term impacts on adult populations. As juveniles show preferential associations with particular coral species, such as corymbose corals, the loss of these growth forms is likely to have the most significant negative impacts on this critical life history stage.

The importance of preferential associations and group cohesion: constraint or optimality

Many animals form social groups, but the adaptive value of being gregarious often differs between individuals. It has been suggested that individuals who gain fewer benefits may only join groups due to constraints on resources. These individuals would prefer to associate loosely with a group, associate strongly with a few preferred individuals and avoid despotic individuals. Alternatively, if joining a group is the optimum decision due to advantages gained from cohesion, individuals may exhibit decreased preferences regarding with whom they associate. We tested these ideas by analysing the social networks of wild winter groups of black-capped chickadees (Poecile atricapillus) in relation to experimental manipulation of resource distribution: three feeders 5 m apart (individuals can maintain contact with the group while also following their social preferences), 40 m apart (increased risk of losing contact while following preferences) and 130 m apart (extremely difficult to follow preferences without losing cohesion). If preferential associations are more important than cohesion, we predicted fewer but stronger connections with decreasing distance between feeders. Dynamic network analysis revealed that distance treatments did change the number of above average strength associations. However, stability of individual centrality was found to decrease when resources were close together and network structure remained similar overall. This suggests individuals maintain cohesion even when alternative foraging choices are available nearby but associate more selectively when given the opportunity. Our results indicate that while individuals will attempt to follow their preferential associations where possible, these are insufficient to cause breakdown in cohesion, possibly due to costs of losing contact with the group. Animals must compromise between associating with preferred individuals and following group consensus. The importance of social preferences can help infer animals’ reasons for joining a group. If group cohesion brings benefits, following group consensus may be more important than individuals’ social preferences. Alternatively, if groups form simply due to lack of resources, following social preferences may be more important than maintaining group cohesion, depending on the costs of losing contact with the group. We examined this by looking at social network structure of black-capped chickadees in relation to resource distribution, expecting changes in network structure as it became easier or harder to exhibit social preferences. We found individuals had fewer strong associations when resources were closer, meaning that networks were more differentiated than when resources were further apart. This suggests that individuals associated more selectively when possible, though this did not appear to change overall network structure.

Structure and wettability of heterogeneous monomolecular films of phospholipids with cholesterol or lauryl gallate

The mica supported Langmuir-Blodgett (LB) monolayers composed of 1,2‑dipalmitoyl‐sn‑glycero‑3‑phosphocholine (DPPC) and 1,2‑dioleoyl‑sn‑glycero‑3‑phosphocholine (DOPC) were used to investigate the effect of cholesterol (Chol) or lauryl gallate (LG) on physicochemical properties of the phospholipid DPPC/DOPC monomolecular film treated as a model leaflet of the bilayer structured membrane. First the surface topography studies of these systems were carried out by means of atomic force microscopy (AFM). Then wettability was investigated via the contact angle measurements and the surface free energy determination. Finally, the time-of-flight secondary ion mass spectrometry (TOF-SIMS) was applied for the surface chemical analysis. Wettability of the monolayers was found to be closely related to the surface chemistry, molecular packing and ordering, miscibility and co-localization of molecules rather than nanoscale roughness. The comparison of the surface polarity determined from the values of contact angle and secondary ion signal intensity provided consistent results. The correlation between the changes of the electron-donor parameter and the 184/57 ratio revealed significance of using the latter quantity as a polarity indicator. The carried out studies show preferential association of components providing a framework for understanding the mechanism of heterogeneities formation within the membrane which reflect the specialization of various regions.

Functionalized polysaccharides with aminoguaiacol: a competition between associative behavior and antibacterial and antioxidant activities

Abstract In a previous study, we presented the development of a series of functionalized carboxymethylpullulan (CMP) grafted with aminoguaiacol (derivative of guaiacol with known antibacterial and antioxidant activities) leading to CMP-G derivatives with various degrees of substitution [DS(Ga)] from 0.16 to 0.58. Our results have shown the efficiency of the grafting both with the evidence of antioxidant and antibacterial activities (Staphylococcus aureus) of the CMP-G derivatives. Nevertheless, an important result has shown surprisingly that such biological activity was not clearly improved with the DS(Ga) unlike the antioxidant activity. These results were probably correlated with a peculiar associative behavior of the derivative (i.e. amphiphilic character) due to the grafted hydrophobic guaiacol groups leading to preferential intramolecular association which was particularly important in the more concentrated regime (polysoap behavior). To complete this study, we propose here two strategies in order to diminish the associative character and notably the polysoap behavior: (i) decrease the DS(Ga) of CMP derivative with a CMP-G0.05 [grafted with a DS(Ga) = 0.05], (ii) conduct the functionalization onto a more rigid polysaccharide backbone as alginate. Our results show a good correlation of the associative physicochemical behaviors with both antioxidant and antibacterial activities. They also confirm the availability of these strategies mainly for the first one (i.e. CMP-G0.05). The main result indicates that the lower is the DS(Ga), the better is the antibacterial activity thanks to a lower associative character. Finally, this study also shows that the grafting of aminoguaiacol is possible onto another anionic polysaccharide (i.e. alginate).

Adaptive partner recruitment can help maintain an intra-guild diversity in mutualistic systems

Mutualisms between assemblages of multiple species or strains (guilds) are considered unstable because of positive feedback between the guilds. Previous studies suggest that negative inter-guild feedback due to asymmetry in the exchange of benefits between the guilds can stabilize them, but preferential association for more beneficial partners may reduce such asymmetry and strengthen the positive inter-guild feedback. Here I develop a replicator dynamics model for mutualistic systems between two host and two symbiont strains to investigate conditions that stabilize mutualisms when feedback between host–symbiont guilds is positive. I assume that one symbiont strain is mutualistic for one host strain but parasitic for the other, whereas the other symbiont strain is the opposite. Hosts recruit their symbionts from the environment and discriminately offer them resources (partner preference), and only mutualistic symbionts return benefits to their hosts. I show that the two host and symbiont strains can coexist under strong partner preference by hosts if they adaptively adjust the number of associating symbionts, even when the intra-host strain competition is not so strong. Interestingly, there can be a stable coexistence equilibrium also under weak partner preference, but it disappears under intermediate levels of partner preference.

Unusual locomotion behaviour preserved within a crocodyliform trackway from the Upper Cretaceous Bayanshiree Formation of Mongolia and its palaeobiological implications

Crocodyliform tracks are reported from the Upper Cretaceous (?Cenomanian-Santonian) Bayanshiree Formation in southeastern Mongolia. Ten tracks are preserved as natural casts, forming a trackway with a quadrupedal gait pattern with a tail trail. All tracks are short and wide, and dominated by toe traces without plantar impressions. Pes tracks are characterized by four deep claw impressions and push-back marks behind them. Manus tracks have shallow claw marks and long, sub-parallel scratch marks behind. The preferential association of the scratch marks with only the distal digit impressions and irregular pattern of footfalls suggests that this trackway was made by a bottom walking and punting crocodyliform under water. This trackway represents the first crocodyliform “swim tracks” in the Late Cretaceous of Asia and the first evidence for punting behaviour of a fossil crocodyliform. The “swim tracks” can be divided into two categories such as bottom walking tracks with punting for moving somewhat more quickly and subaqueous walking tracks without punting to be associated with slower underwater speeds. The tracks show that crocodylians had adopted a bottom walking behaviour similar to extant crocodylians by Cretaceous times.

PF227 PROGNOSTIC VALUE OF CLONAL HEMATOPOIESIS‐MUTATIONS DETECTED AT DIAGNOSIS IN ACUTE MYELOID LEUKEMIA PATIENTS WITH NORMAL KARYOTYPE

Background:Mutations in DNA and chromatin regulation genes have been associated with clonal hematopoiesis (CH) in older healthy subjects, but are also involved in leukemogenesis occurring as early events. In AML patients, the prognostic role of CH‐mutations detected at diagnosis has been assessed mainly by investigating single mutations, with diverging results. Thus, the significance of pre‐treatment CH‐mutations as a group remains to be elucidated.Aims:To investigate the distribution and clinical impact of CH‐mutations detected at diagnosis in AML patients with normal karyotype and treated with chemotherapy eventually followed by allogeneic hematopoietic stem cell transplant (alloHSCT) within the prospective NILG trial 02/06 [ClinicalTrials.gov Identifier: NCT00495287].Methods:Out of 572 newly diagnosed AML patients enrolled into the trial, 270 had a normal karyotype. For 213 of them, a molecular profile was obtained at diagnosis with standard approach and targeted NGS on peripheral blood and bone marrow samples. CH‐mutations were defined as DNMT3A, TET2, ASXL1, IDH1 and IDH2. Based on the available data, 209 patients were re‐classified as per the 2017 European Leukemia Net (ELN) guidelines. All patients were treated with intensive chemotherapy eventually followed by consolidative alloHSCT.Results:At least one CH‐mutation was reported for 131 out of 213 evaluable patients (61.5%), while 82 patients had no CH‐mutations (38.5%). Patients carrying CH‐mutations were older in comparison with patients without CH‐mutations (median age 53 vs 47 years, P = 0.0003). No preferential association was found in respect of AML type (i.e. de novo vs secondary AML, P = 0.25). The most recurrent CH‐mutation was DNMT3A (83/131), followed by TET2 (32/131), IDH2 (26/131), IDH1 (20/131) and ASXL1 (18/131). A single CH‐mutation was observed in 65% of patients, while 33.5% had a double mutation and 1.5% a triple mutation. Overall, CH‐mutations were detected across all ELN risk groups. The likelihood of carrying a CH‐mutation was significantly increased in patients with a NPM1 mutation (P &lt; 0.0001), while the opposite was reported for patients with a biallelic CEBPa mutation (P &lt; 0.0001). Taken together, CH‐mutations did not affect the 5‐years disease free survival (DFS) and overall survival (OS) (46% vs 54%, P = 0.45; and 50% vs 55%, P = 0.21). However, within the ELN risk categories, the presence of CH‐mutations negatively affected the 5‐years DFS (86% vs 59%, P = 0.03) and OS (86% vs 71%, P = 0.09) in patients in the favorable risk group, while these outcomes were not affected in the intermediate and adverse risk groups. By analyzing each CH‐mutation separately, TET2 emerged as an independent risk factor for the achievement of CR [OR 0.25 (95% CI 0.08–0.7), P = 0.008], but not for OS [OR 1.56 (95% CI 0.89–2.75), P = 0.12]. Finally, 186 patients who received a consolidative alloHSCT in first CR were investigated, 107 of them carrying CH‐mutations. AlloHSCT provided a significant benefit in terms of OS for the whole study population (P = 0.001), irrespective of the presence of CH‐mutations (P = 0.87).Summary/Conclusion:CH‐mutations are frequently detected at diagnosis in AML patients with normal karyotype across all ELN risk groups, but more likely in NPM1 mutated patients. Overall, the presence of CH‐mutations is not associated with worse outcomes except for patients within the ELN favorable risk group. These findings suggest that an active search of these mutations might refine the risk of relapse in patients considered at favorable risk, while their role is limited in patients with more aggressive disease profile.image

MRNA association by aminoacyl tRNA synthetase occurs at a putative anticodon mimic and autoregulates translation in response to tRNA levels.

Aminoacyl-tRNA synthetases (aaRSs) are well studied for their role in binding and charging tRNAs with cognate amino acids. Recent RNA interactome studies had suggested that these enzymes can also bind polyadenylated RNAs. Here, we explored the mRNA repertoire bound by several yeast aaRSs. RNA immunoprecipitation (RIP) followed by deep sequencing revealed unique sets of mRNAs bound by each aaRS. Interestingly, for every tested aaRSs, a preferential association with its own mRNA was observed, suggesting an autoregulatory process. Self-association of histidyl-tRNA synthetase (HisRS) was found to be mediated primarily through binding to a region predicted to fold into a tRNAHis anticodon-like structure. Introducing point mutations that are expected to disassemble this putative anticodon mimic alleviated self-association, concomitant with increased synthesis of the protein. Finally, we found that increased cellular levels of uncharged tRNAHis lead to reduced self-association and increased HisRS translation, in a manner that depends on the anticodon-like element. Together, these results reveal a novel post-transcriptional autoregulatory mechanism that exploits binding mimicry to control mRNA translation according to tRNA demands.

Maize root‐derived C in soil and the role of physical protection on its relative stability over shoot‐derived C

Evidence is accumulating that belowground crop residues contribute more efficiently to the build‐up and maintenance of native soil organic carbon (SOC) than aboveground plant parts. We corroborated previous testing of the hypothesis that root‐C would preferentially accumulate in soil microaggregates, where it is physically protected against microbially mediated decomposition. In three European field trials with C3 to C4 crop transitions, we compared the content of maize‐C (Zea mays L.) in soil from rotations with grain maize (MG) or silage maize (MS) (i.e. with incorporation of roots and shoots or roots only). After decades of maize cultivation, SOC content did not differ within three out of four MG–MS pairs, although obviously larger amounts of shoot biomass were added to soil in the case of MG. We found that relative contribution of roots was on average 3.5 times more than shoots to the build‐up of SOC per equivalent mass of residue C added to soils. Preferential occlusion of root‐C as silt‐sized intra‐microaggregate particulate organic matter (iPOM) was not observed. There were much larger effects from shoot incorporation on maize‐C in the &gt;53‐μm fraction and free silt and clay. Storage of root‐C as sand‐sized iPOM was not quantified here, but first estimates suggested that physical entrapment at this level could only partly explain the longevity of root‐C in soil. We reconfirm the relative stability of root‐C in soil, but do not conclude that this stems from preferential physical entrapment over shoot‐C. Future work should investigate the cause of preferential root‐C association with the clay‐sized fraction and if this occurs before or after microbial processing.Highlights The hypothesized preferential physical stabilization of root‐C was assessed. Aboveground biomass had a minor effect on SOC storage in European long‐term trials. Contribution of maize root‐C to maintenance of SOC was three‐fold that of shoot‐C inputs. There was no preferential occlusion of root‐C in silt‐sized microaggregates.

Phospholipid distributions in purple phototrophic bacteria and LH1-RC core complexes

In contrast to plants, algae and cyanobacteria that contain glycolipids as the major lipid components in their photosynthetic membranes, phospholipids are the dominant lipids in the membranes of anoxygenic purple phototrophic bacteria. Although the phospholipid compositions in whole cells or membranes are known for a limited number of the purple bacteria, little is known about the phospholipids associated with individual photosynthetic complexes. In this study, we investigated the phospholipid distributions in both membranes and the light-harvesting 1-reaction center (LH1-RC) complexes purified from several purple sulfur and nonsulfur bacteria. 31P NMR was used for determining the phospholipid compositions and inductively coupled plasma atomic emission spectroscopy was used for measuring the total phosphorous contents. Combining these two techniques, we could determine the numbers of specific phospholipids in the purified LH1-RC complexes. A total of approximate 20–30 phospholipids per LH1-RC were detected as the tightly bound lipids in all species. The results revealed that while cardiolipin (CL) exists as a minor component in the membranes, it became the most abundant phospholipid in the purified core complexes and the sum of CL and phosphatidylglycerol accounted for more than two thirds of the total phospholipids for most species. Preferential association of these anionic phospholipids with the LH1-RC is discussed in the context of the recent high-resolution structure of this complex from Thermochromatium (Tch.) tepidum. The detergent lauryldimethylamine N-oxide was demonstrated to selectively remove phosphatidylethanolamine from the membrane of Tch. tepidum.