Regulation of the first committed step of peptidoglycan precursor synthesis by MurA‐enzyme homologs has recently taken center stage in many different bacteria. In different low‐GC Gram‐positive ...bacteria, regulation of this step has been shown to be regulated by phosphorylation of homologs of the IreB/ReoM regulatory protein by PASTA‐domain Ser/Thr‐protein kinases. In this issue, Mascari, Little, and Kristich determine this regulatory pathway and its links to resistance to cephalosporin β‐lactam antibiotics in the major human pathogen, Enterococcus faecalis (Efa). Unbiased genetic selections identified MurAA (MurA‐family homolog) as the downstream target of IreB regulation in the absence of the IreK Ser/Thr‐protein kinase. Physiological and biochemical approaches, including determination of MICs to ceftriaxone, Western blotting of MurAA cellular amounts, isotope incorporation into peptidoglycan sacculi, and thermal‐shift binding assays of purified proteins, demonstrated that unphosphorylated IreB, together with proteins MurAB (MurZ‐family homolog), and ReoY(Efa) negatively regulate MurAA stability and cellular amount by the ClpCP protease. Importantly, this paper supports the idea that ceftriaxone stimulates phosphorylation of IreB, which leads to increased cellular MurAA amount and precursor pathway flux required for E. faecalis cephalosporin resistance. Overall, findings in this paper significantly contribute to understanding variations of this central regulatory pathway in other low‐GC Gram‐positive bacteria.
Bruton tyrosine kinase (BTK) is a critical effector molecule for B cell development and plays a major role in lymphoma genesis. Ibrutinib is the first-generation BTK inhibitor. Ibrutinib has ...off-target effects on EGFR, ITK, and Tec family kinases, which explains the untoward effects of ibrutinib. Resistance to ibrutinib was also reported. The C481S mutation in the BTK kinase domain was reported to be a major mechanism of resistance to ibrutinib. This review summarizes the clinical development of novel BTK inhibitors, ACP-196 (acalabrutinib), ONO/GS-4059, and BGB-3111.
We report on the experimental realization of a conservative optical lattice for cold atoms with a subwavelength spatial structure. The potential is based on the nonlinear optical response of ...three-level atoms in laser-dressed dark states, which is not constrained by the diffraction limit of the light generating the potential. The lattice consists of a one-dimensional array of ultranarrow barriers with widths less than 10 nm, well below the wavelength of the lattice light, physically realizing a Kronig-Penney potential. We study the band structure and dissipation of this lattice and find good agreement with theoretical predictions. Even on resonance, the observed lifetimes of atoms trapped in the lattice are as long as 44 ms, nearly 10^{5} times the excited state lifetime, and could be further improved with more laser intensity. The potential is readily generalizable to higher dimensions and different geometries, allowing, for example, nearly perfect box traps, narrow tunnel junctions for atomtronics applications, and dynamically generated lattices with subwavelength spacings.
Quantum simulations with ultracold atoms typically create atomic wavefunctions with structures at optical length scales, where direct imaging suffers from the diffraction limit. In analogy to ...advances in optical microscopy for biological applications, we use a non-linear atomic response to surpass the diffraction limit. Exploiting quantum interference, we demonstrate imaging with super-resolution of λ/50 and excellent temporal resolution of 500 ns. We characterize our microscope's performance by measuring the ensemble averaged probability density of atoms within the unit cells of an optical lattice, and observe the dynamics of atoms excited into motion. This approach can be readily applied to image any atomic or molecular system, as long as it hosts a three-level system.
Bacterial peptidoglycan (PG) synthesis requires strict spatiotemporal organization to reproduce specific cell shapes. In ovoid‐shaped Streptococcus pneumoniae (Spn), septal and peripheral ...(elongation) PG synthesis occur simultaneously at midcell. To uncover the organization of proteins and activities that carry out these two modes of PG synthesis, we examined Spn cells vertically oriented onto their poles to image the division plane at the high lateral resolution of 3D‐SIM (structured‐illumination microscopy). Labeling with fluorescent D‐amino acids (FDAA) showed that areas of new transpeptidase (TP) activity catalyzed by penicillin‐binding proteins (PBPs) separate into a pair of concentric rings early in division, representing peripheral PG (pPG) synthesis (outer ring) and the leading‐edge (inner ring) of septal PG (sPG) synthesis. Fluorescently tagged PBP2x or FtsZ locate primarily to the inner FDAA‐marked ring, whereas PBP2b and FtsX remain in the outer ring, suggesting roles in sPG or pPG synthesis, respectively. Pulses of FDAA labeling revealed an arrangement of separate regularly spaced “nodes” of TP activity around the division site of predivisional cells. Tagged PBP2x, PBP2b, and FtsX proteins also exhibited nodal patterns with spacing comparable to that of FDAA labeling. Together, these results reveal new aspects of spatially ordered PG synthesis in ovococcal bacteria during cell division.
High‐resolution images of vertically oriented Streptococcus pneumoniae cells reveal concentric rings of PBP transpeptidase (TP) activity corresponding to the leading edge of the septal annulus (inner ring) and the midcell outer ring of elongating peptidoglycan (PG) synthesis. The rings serve as fiducial markers for assigning proteins to the septal (PBP2x and FtsZ) or elongation (PBP2b, FtsX) PG synthesis machines. In predivisional cells, PG synthesis proteins and PBP transpeptidase activity are arranged in patterns of regularly spaced nodes, whose spacing is perturbed in mutants.
RodZ of rod‐shaped bacteria functions to link MreB filaments to the Rod peptidoglycan (PG) synthase complex that moves circumferentially perpendicular to the long cell axis, creating hoop‐like ...sidewall PG. Ovoid‐shaped bacteria, such as Streptococcus pneumoniae (pneumococcus; Spn) that lack MreB, use a different modality for peripheral PG elongation that emanates from the midcell of dividing cells. Yet, S. pneumoniae encodes a RodZ homolog similar to RodZ in rod‐shaped bacteria. We show here that the helix‐turn‐helix and transmembrane domains of RodZ(Spn) are essential for growth at 37°C. ΔrodZ mutations are suppressed by Δpbp1a, mpgA(Y488D), and ΔkhpA mutations that suppress ΔmreC, but not ΔcozE. Consistent with a role in PG elongation, RodZ(Spn) co‐localizes with MreC and aPBP1a throughout the cell cycle and forms complexes and interacts with PG elongasome proteins and regulators. Depletion of RodZ(Spn) results in aberrantly shaped, non‐growing cells and mislocalization of elongasome proteins MreC, PBP2b, and RodA. Moreover, Tn‐seq reveals that RodZ(Spn), but not MreCD(Spn), displays a specific synthetic‐viable genetic relationship with aPBP1b, whose function is unknown. We conclude that RodZ(Spn) acts as a scaffolding protein required for elongasome assembly and function and that aPBP1b, like aPBP1a, plays a role in elongasome regulation and possibly peripheral PG synthesis.
This paper establishes RodZ as an essential scaffolding protein required for the assembly and function of the elongasome that synthesizes peripheral peptidoglycan (pPG) in Streptococcus pneumoniae, which lacks an MreB homolog. (Top panel) The assembly hierarchy mediated by RodZ(Spn). (Bottom panel) This paper also reports synthetic‐viable, suppressor relationships between Class A aPBP1b and aPBP1a and components of the core pPG elongasome, suggestive of failsafe bypass mechanisms that restore function of the pPG elongasome and viability.
We measured total mercury (THg) and monomethyl mercury (MMHg) concentrations and mercury (Hg) isotopic compositions in sediment and aquatic organisms from the Yuba River (California, USA) to identify ...Hg sources and biogeochemical transformations downstream of a historical gold mining region. Sediment THg concentrations and δ202Hg decreased from the upper Yuba Fan to the lower Yuba Fan and the Feather River. These results are consistent with the release of Hg during gold mining followed by downstream mixing and dilution. The Hg isotopic composition of Yuba Fan sediment (δ202Hg = −0.38 ± 0.17‰ and Δ199Hg = 0.04 ± 0.03‰; mean ± 1 SD, n = 7) provides a fingerprint of inorganic Hg (IHg) that could be methylated locally or after transport downstream. The isotopic composition of MMHg in the Yuba River food web was estimated using biota with a range of %MMHg (the percent of THg present as MMHg) and compared to IHg in sediment, algae, and the food web. The estimated δ202Hg of MMHg prior to photodegradation (−1.29 to −1.07‰) was lower than that of IHg and we suggest this is due to mass-dependent fractionation (MDF) of up to −0.9‰ between IHg and MMHg. This result is in contrast to net positive MDF (+0.4 to +0.8‰) previously observed in lakes, estuaries, coastal oceans, and forests. We hypothesize that this unique relationship could be due to differences in the extent or pathway of biotic MMHg degradation in stream environments.
Floquet engineering or coherent time-periodic driving of quantum systems has been successfully used to synthesize Hamiltonians with novel properties. In ultracold atomic systems, this has led to ...experimental realizations of artificial gauge fields, topological bandstructures, and observation of dynamical localization, to name a few. Here we present a Floquet-based framework to stroboscopically engineer Hamiltonians with spatial features and periodicity below the diffraction limit of light used to create them by time-averaging over various configurations of a 1D optical Kronig-Penney (KP) lattice. The KP potential is a lattice of narrow subwavelength barriers spaced by half the optical wavelength (λ/2) and arises from the nonlinear optical response of the atomic dark state. Stroboscopic control over the strength and position of this lattice requires time-dependent adiabatic manipulation of the dark-state spin composition. We investigate adiabaticity requirements and shape our time-dependent light fields to respect the requirements. We apply this framework to show that a λ/4-spaced lattice can be synthesized using realistic experimental parameters as an example, discuss mechanisms that limit lifetimes in these lattices, explore candidate systems and their limitations, and treat adiabatic loading into the ground band of these lattices.
The effects of three antibiotics (erythromycin, ciprofloxacin and sulfamethoxazole) on photosynthesis process of
Selenastrum capricornutum were investigated by determining a battery of parameters ...including photosynthetic rate, chlorophyll fluorescence, Hill reaction, and ribulose-1.5-bisphosphate carboxylase activity, etc. The results indicated that three antibiotics could significantly inhibit the physiological progress including primary photochemistry, electron transport, photophosphorylation and carbon assimilation. Erythromycin could induce acute toxic effects at the concentration of 0.06
mg
L
−1, while the same results were exhibited for ciprofloxacin and sulfamethoxazole at higher than 1.0
mg
L
−1. Erythromycin was considerably more toxic than ciprofloxacin and sulfamethoxazole and may pose a higher potential risk to the aquatic ecosystem. Some indices like chlorophyll fluorescence, Mg
2+-ATPase activity and RuBPCase activity showed a high specificity and sensitivity to the exposure of erythromycin, and may be potentially used as candidate biomarkers for the exposure of the macrolide antibiotics.
The change in sign of the interaction force constant between element-hydrogen stretching modes of trans-dihydrides of the d block and p block elements is analyzed for the first time. As the ...transition metal M approaches group 12, the higher energy symmetric trans-H–M–H vibration νsym approaches the energy of the antisymmetric vibration νasym. Crossing to group 13 elements E, the trans-H–E–H vibration νsym increasingly drops below νasym. This reversal is attributed to the d orbital that participates in the H–M–H bonding but is nonbonding in the H–E–H compounds. DFT calculations are used to probe the energetics of isoelectronic triatomic H–M–H n+ and H–E–H n− to reveal this trend and also to demonstrate that the magnitude of these interactions (νgap) increases down groups 11, 12, and 14 but remains fairly constant for group 13. They are also used to show that this reversal is seen in the transition state for hydride transfer to CO2 from the model compounds trans-NiH2(porphyrin) and trans-EH2(porphyrin), E = Si and Ge in their singlet states.
PDF
