Structural basis for the function of Tim50 in the mitochondrial presequence translocase

Many mitochondrial proteins are synthesized as preproteins carrying amino-terminal presequences in the cytosol. The preproteins are imported by the translocase of the outer mitochondrial membrane and the presequence translocase of the inner membrane. Tim50 and Tim23 transfer preproteins through the intermembrane space to the inner membrane. We report the crystal structure of the intermembrane space domain of yeast Tim50 to 1.83 Å resolution. A protruding β-hairpin of Tim50 is crucial for interaction with Tim23, providing a molecular basis for the cooperation of Tim50 and Tim23 in preprotein translocation to the protein-conducting channel of the mitochondrial inner membrane.     

1H, 15N and 13C chemical shift assignments for the winged helix domains of two archeal MCM C-termini

High-fidelity replication guarantees the stable inheritance of genetic information stored in the DNA of living organisms. The minichromosome maintenance (MCM) complex functions as replicative DNA-unwinding helicase and has been identified as one key player in the replication process of archea and eukarya. Despite the availability of considerable structural information on archeal MCMs, such information was missing for their C-terminal domain. In order to obtain more detailed structural information, we assigned the NMR chemical shifts for backbone and side chain nuclei for the MCM C-terminal winged helix domains of the archeal species Methanothermobacter thermautrophicus and Sulfolobus solfataricus.     

Specific Interaction of the Unmodified Bacteriocin Lactococcin 972 with the Cell Wall Precursor Lipid II

Lactococcin 972 (Lcn972) is a nonlantibiotic bacteriocin that inhibits septum biosynthesis in Lactococcus lactis rather than forming pores in the cytoplasmic membrane. In this study, a deeper analysis of the molecular basis of the mode of action of Lcn972 was performed. Of several lipid cell wall precursors, only lipid II antagonized Lcn972 inhibitory activity in vivo. Likewise, Lcn972 only coprecipitated with lipid II micelles. This bacteriocin inhibited the in vitro polymerization of lipid II by the recombinant S. aureus PBP2 and the addition to lipid II of the first glycine catalyzed by FemX. These experiments demonstrate that Lcn972 specifically interacts with lipid II, the substrate of both enzymes. In the presence of Lcn972, nisin pore formation was partially hindered in whole cells. However, binding of Lcn972 to lipid II could not compete with nisin in lipid II-doped 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) liposomes, possibly indicating a distinct binding site. The existence of a putative cotarget for Lcn972 activity is discussed in the context of its narrow inhibitory spectrum and the localized action at the division septum. To our knowledge, this is the first unmodified bacteriocin that binds to the cell wall precursor lipid II.     

Crop processing of <Emphasis Type="Italic">Olea europaea</Emphasis> L.: an experimental approach for the interpretation of archaeobotanical olive remains

Archaeobotanical research, ethnographic observations and laboratory experiments are put together to create model sequences of olive processing, which are developed, presented and explored as an aid for the interpretation of rich archaeobotanical assemblages of Olea. We conclude that the remains of different processing stages are reasonably distinctive in the archaeobotanical record and assist in the identification of different types of olive remains, such as fragmented olive stones, the inner kernels, and fruit flesh     

Engagement of CD22 on B cells with the monoclonal antibody epratuzumab stimulates the phosphorylation of upstream inhibitory signals of the B cell receptor

The binding of antigen to the B cell receptor (BCR) results in a cascade of signalling events that ultimately drive B cell activation. Uncontrolled B cell activation is regulated by negative feedback loops that involve inhibitory co-receptors such as CD22 and CD32B that exert their functions following phosphorylation of immunoreceptor tyrosine-based inhibition motifs (ITIMs). The CD22-targeted antibody epratuzumab has previously been shown to inhibit BCR-driven signalling events, but its effects on ITIM phosphorylation of CD22 and CD32B have not been properly evaluated. The present study therefore employed both immunoprecipitation and flow cytometry approaches to elucidate the effects of epratuzumab on direct phosphorylation of key tyrosine (Tyr) residues on both these proteins, using both transformed B cell lines and primary human B cells. Epratuzumab induced the phosphorylation of Tyr⁸²² on CD22 and enhanced its co-localisation with SHP-1. Additionally, in spite of high basal phosphorylation of other key ITIMs on CD22, in primary human B cells epratuzumab also enhanced phosphorylation of Tyr⁸⁰⁷, a residue involved in the recruitment of Grb2. Such initiation events could explain the effects of epratuzumab on downstream signalling in B cells. Finally, we were able to demonstrate that epratuzumab stimulated the phosphorylation of Tyr²⁹² on the low affinity inhibitory Fc receptor CD32B which would further attenuate BCR-induced signalling. Together, these data demonstrate that engagement of CD22 with epratuzumab leads to the direct phosphorylation of key upstream inhibitory receptors of BCR signalling and may help to explain how this antibody modulates B cell function.     

Habitat properties and plant traits interact as drivers of non‐native plant species’ seed production at the local scale

To answer the long‐standing question if we can predict plant invader success based on characteristics of the environment (invasibility) or the invasive species (invasiveness), or the combination of both, there is a need for detailed observational studies in which habitat properties, non‐native plant traits, and the resulting invader success are locally measured. In this study, we assess the interaction of gradients in the environmental and trait space on non‐native species fitness, expressed as seed production, for a set of 10 invasive and noninvasive non‐native species along a wide range of invaded sites in Flanders. In our multidimensional approach, most of the single environmental gradients (temperature, light availability, native plant species diversity, and soil fertility) and sets of non‐native plant traits (plant size, photosynthesis, and foliar chemical attributes) related positively with invader seed production. Yet correlation with seed production was much stronger when several environmental gradients were assessed in interaction, and even more so when we combined plant traits and habitat properties. The latter increased explanatory power of the models on average by 25% for invasive and by 7% for noninvasive species. Additionally, we report a 70‐fold higher seed production in invasive than in noninvasive species and fundamentally different correlations of seed production with plant traits and habitat properties in noninvasive versus invasive species. We conclude that locally measured traits and properties deserve much more attention than they currently get in invasion literature and thus encourage further studies combining this level of detail with the generality of a multiregion and multispecies approach across different stages of invasion.