Structure of the Bacillus subtilis 70S ribosome reveals the basis for species-specific stalling

Ribosomal stalling is used to regulate gene expression and can occur in a species-specific manner. Stalling during translation of the MifM leader peptide regulates expression of the downstream membrane protein biogenesis factor YidC2 (YqjG) in Bacillus subtilis, but not in Escherichia coli. In the absence of structures of Gram-positive bacterial ribosomes, a molecular basis for species-specific stalling has remained unclear. Here we present the structure of a Gram-positive B. subtilis MifM-stalled 70S ribosome at 3.5-3.9 angstrom, revealing a network of interactions between MifM and the ribosomal tunnel, which stabilize a non-productive conformation of the PTC that prevents aminoacyl-tRNA accommodation and thereby induces translational arrest. Complementary genetic analyses identify a single amino acid within ribosomal protein L22 that dictates the species specificity of the stalling event. Such insights expand our understanding of how the synergism between the ribosome and the nascent chain is utilized to modulate the translatome in a species-specific manner

Involvement of RhoA-mediated Ca(2+ )sensitization in antigen-induced bronchial smooth muscle hyperresponsiveness in mice

BACKGROUND: It has recently been suggested that RhoA plays an important role in the enhancement of the Ca(2+ )sensitization of smooth muscle contraction. In the present study, a participation of RhoA-mediated Ca(2+ )sensitization in the augmented bronchial smooth muscle (BSM) contraction in a murine model of allergic asthma was examined. METHODS: Ovalbumin (OA)-sensitized BALB/c mice were repeatedly challenged with aerosolized OA and sacrificed 24 hours after the last antigen challenge. The contractility and RhoA protein expression of BSMs were measured by organ-bath technique and immunoblotting, respectively. RESULTS: Repeated OA challenge to sensitized mice caused a BSM hyperresponsiveness to acetylcholine (ACh), but not to high K(+)-depolarization. In α-toxin-permeabilized BSMs, ACh induced a Ca(2+ )sensitization of contraction, which is sensitive to Clostridium botulinum C3 exoenzyme, indicating that RhoA is implicated in this Ca(2+ )sensitization. Interestingly, the ACh-induced, RhoA-mediated Ca(2+ )sensitization was significantly augmented in permeabilized BSMs of OA-challenged mice. Moreover, protein expression of RhoA was significantly increased in the hyperresponsive BSMs. CONCLUSION: These findings suggest that the augmentation of Ca(2+ )sensitizing effect, probably via an up-regulation of RhoA protein, might be involved in the enhanced BSM contraction in antigen-induced airway hyperresponsiveness

YidC assists the stepwise and stochastic folding of membrane proteins

How chaperones, insertases and translocases facilitate insertion and folding of complex cytoplasmic proteins into cellular membranes is not fully understood. Here, we utilize single-molecule force spectroscopy to observe YidC, a transmembrane chaperone/insertase, sculpting the folding trajectory of the polytopic α-helical membrane protein lactose permease (LacY). In the absence of YidC, unfolded LacY inserts individual structural segments into the membrane; however, misfolding dominates the process so that folding cannot be completed. YidC prevents LacY from misfolding by stabilizing the unfolded state from which LacY inserts structural segments stepwise into the membrane until folding is completed. During stepwise insertion, YidC and membrane together stabilize the transient folds. Remarkably, the order of insertion of structural segments is stochastic, thereby indicating that LacY can fold along variable pathways towards the native structure. Since YidC is essential in membrane protein biogenesis and LacY a paradigm for the major facilitator superfamily, our observations have general relevance

Cancer Stem Cells: From Birth to Death

Abstract Conspicuous investigations have proven the role of cancer stem cells (CSCs) in the onset and progression of a plethora of liquid and solid neoplasms. CSCs are endowed with the capability of initiating tumor growth and becoming dormant at distant organ sites just waiting for optimal conditions amenable for metastatic outgrowth. This cancer subpopulation is inherently resistant to anticancer therapeutics, and its targeting could avoid metastatic disease, which is largely incurable, and clinical relapses. CSCs are considered the Achilles heel of cancer. However, many efforts are necessary to identify univocal CSC markers as well as specific CSC biomarkers of therapeutic response. Here, we summarize CSCs’ peculiarities and highlight novel anticancer compounds coping with the hallmarks of CSCs, comprising the resistance to cell death, their quiescent state, the immune suppression, the epithelial to mesenchymal transition (EMT), and their metabolic adaptation to a hostile microenvironment