A distinct structural region of the prokaryotic ubiquitin-like protein (Pup) is recognized by the N-terminal domain of the proteasomal ATPase Mpa

AbstractThe mycobacterial ubiquitin-like protein Pup is coupled to proteins, thereby rendering them as substrates for proteasome-mediated degradation. The Pup-tagged proteins are recruited by the proteasomal ATPase Mpa (also called ARC). Using a combination of biochemical and NMR methods, we characterize the structural determinants of Pup and its interaction with Mpa, demonstrating that Pup adopts a range of extended conformations with a short helical stretch in its C-terminal portion. We show that the N-terminal coiled-coil domain of Mpa makes extensive contacts along the central region of Pup leaving its N-terminus unconstrained and available for other functional interactions.Structured summaryMINT-7262427: pup (uniprotkb:B6DAC1) binds (MI:0407) to mpa (uniprotkb:Q0G9Y7) by pull down (MI:0096) MINT-7262440: mpa (uniprotkb:Q0G9Y7) and pup (uniprotkb:B6DAC1) bind (MI:0407) by isothermal titration calorimetry (MI:0065

Stoichiometric constraints on phytoplankton resource use efficiency in monocultures and mixtures

International audienceA central concept for understanding the mechanisms linking diversity and primary production or more general, ecosystem functioning, is resource use efficiency (RUE). It quantifies the amount of biomass production over time relative to unit resource supplied, that is, represents a quota of matter use efficiency. Given anthropogenic alterations of biogeochemical cycles, the consequent changes in supply rate and especially supply ratio of nutrients will change. Using four species of freshwater phytoplankton, and their mixture, we asked how the RUE for nitrogen and phosphorus depends on the stoichiometry of resource supply and how this differs between single species and their mixture. We conducted a factorial laboratory experiment spanning 25 different nutrient supply treatments with differing absolute and relative nitrogen (N) and phosphorus (P) concentrations. N and P supply increased biomass production and decreased C : nutrient ratios and RUE for the respective nutrient, but always significantly affected by the supply of the respective other nutrient. Biomass peaked at molar N : P supply ratios above the Redfield ratio (18–22). Species tended to respond similarly to the resource gradients. Consequently, mixtures outperformed the component species only during early growth responses, but not regarding maximum biomass and RUE. Bioassays performed at the end of the main experiment revealed predominance of N‐limitation, but again strongly depending on the interaction between both nutrient gradients. Our study suggests that stoichiometric constraints of resource incorporation and RUE need to be accounted for when studying the response of phytoplankton to natural and anthropogenic variation in resource availability

Diagnostic Evaluation of Detrimental Phenomena in High-Power Lithium-Ion Batteries

A pouch-type lithium-ion cell, with graphite anode and LiNi{sub 0.8}Co{sub 0.15}Al{sub 0.05}O{sub 2} cathode, was cycled at C/2 over 100% depth of discharge (DOD) at ambient temperature. The LiNi{sub 0.8}Co{sub 0.15}Al{sub 0.05}O{sub 2} composite cathode was primarily responsible for the significant impedance rise and capacity fade observed in that cell. The processes that led to this impedance rise were assessed by investigating the cathode surface electronic conductance, surface structure, composition, and state of charge at the microscopic level with the use of local probe techniques. Raman microscopy mapping of the cathode surface provided evidence that the state of charge of individual LiNi{sub 0.8}Co{sub 0.15}Al{sub 0.05}O{sub 2} particles was non-uniform despite the deep discharge at the end of cell testing. Current-sensing atomic force microscopy imaging revealed that the cathode surface electronic conductance diminished significantly in the tested cells. Loss of contact of active material particles with the carbon matrix and thin film formation via electrolyte decomposition not only led to LiNi{sub 0.8}Co{sub 0.15}Al{sub 0.05}O{sub 2} particle isolation and contributed to cathode interfacial charge-transfer impedance but also accounted for the observed cell power and capacity loss

The Redox State of SECIS Binding Protein 2 Controls Its Localization and Selenocysteine Incorporation Function

Selenoproteins are central controllers of cellular redox homeostasis. Incorporation of selenocysteine (Sec) into selenoproteins employs a unique mechanism to decode the UGA stop codon. The process requires the Sec insertion sequence (SECIS) element, tRNA(Sec), and protein factors including the SECIS binding protein 2 (SBP2). Here, we report the characterization of motifs within SBP2 that regulate its subcellular localization and function. We show that SBP2 shuttles between the nucleus and the cytoplasm via intrinsic, functional nuclear localization signal and nuclear export signal motifs and that its nuclear export is dependent on the CRM1 pathway. Oxidative stress induces nuclear accumulation of SBP2 via oxidation of cysteine residues within a redox-sensitive cysteine-rich domain. These modifications are efficiently reversed in vitro by human thioredoxin and glutaredoxin, suggesting that these antioxidant systems might regulate redox status of SBP2 in vivo. Depletion of SBP2 in cell lines using small interfering RNA results in a decrease in Sec incorporation, providing direct evidence for its requirement for selenoprotein synthesis. Furthermore, Sec incorporation is reduced substantially after treatment of cells with agents that cause oxidative stress, suggesting that nuclear sequestration of SBP2 under such conditions may represent a mechanism to regulate the expression of selenoproteins