The molecular architecture of engulfment during Bacillus subtilis sporulation.

The study of bacterial cell biology is limited by difficulties in visualizing cellular structures at high spatial resolution within their native milieu. Here, we visualize Bacillus subtilis sporulation using cryo-electron tomography coupled with cryo-focused ion beam milling, allowing the reconstruction of native-state cellular sections at molecular resolution. During sporulation, an asymmetrically-positioned septum generates a larger mother cell and a smaller forespore. Subsequently, the mother cell engulfs the forespore. We show that the septal peptidoglycan is not completely degraded at the onset of engulfment. Instead, the septum is uniformly and only slightly thinned as it curves towards the mother cell. Then, the mother cell membrane migrates around the forespore in tiny finger-like projections, whose formation requires the mother cell SpoIIDMP protein complex. We propose that a limited number of SpoIIDMP complexes tether to and degrade the peptidoglycan ahead of the engulfing membrane, generating an irregular membrane front

The yeast p24 complex regulates gpi-anchored protein Transport and quality control by monitoring anchor remodeling

Glycosylphosphatidylinositol (GPI)-anchored proteins are secretory proteins that are attached to the cell surface of eukaryotic cells by a glycolipid moiety. Once GPI anchoring has occurred in the lumen of the endoplasmic reticulum (ER), the structure of the lipid part on the GPI anchor undergoes a remodeling process prior to ER exit. In this study, we provide evidence suggesting that the yeast p24 complex, through binding specifically to GPI- anchored proteins in an anchor-dependent manner, plays a dual role in their selective traffick - ing. First, the p24 complex promotes efficient ER exit of remodeled GPI-anchored proteins after concentration by connecting them with the COPII coat and thus facilitates their incorpo - ration into vesicles. Second, it retrieves escaped, unremodeled GPI-anchored proteins from the Golgi to the ER in COPI vesicles. Therefore the p24 complex, by sensing the status of the GPI anchor, regulates GPI-anchored protein intracellular transport and coordinates this with correct anchor remodelin

アレルギー性気道炎症におけるAT II la受容体の機能解析

Chronic airway inflammation and airway hyperresponsiveness (AHR) are fundamental features leading to airway narrowing in bronchial asthma. Airway inflammation in asthmatics is characterized with the accumulation and activation of inflammatory cells such as eosinophils and mast cells, which is orchestrated by a network of Th2 cytokines, such as IL-4 and IL-5, released mainly from CD^+_4 T lymphocytes. The peptide hormone angiotensin II (AT II) plays an important role in the regulation of arterial blood pressure. Plasma levels of renin and AT II were reported to be elevated during acute exacerbation of asthma, and studies using type 1 AT II receptor (AT1) antagonist (ARE) suggested the involvement of the receptor in the pathogenesis of asthma. However, the pathogenic roles of AT II and AT1 in asthmatic airway inflammation remains elusive. Therefore, we investigated the effect of ATla gene deletion (ATlaKO) on allergen-induced airway inflammation using a murine model of allergic asthma. In sensitized wild type mice (WT), the numbers of inflammatory cells in bronchoalveolar lavage fluids (BALF) were increased with a peak on 5 days after antigen challenge. In ATlaKO mice, in contrast, those were increased with two peaks on 3 and 7 days, which were significantly higher than in WT. The contents of IL-4 and IL-5 in BALF of ATlaKO mice 1 day after the challenge were significantly higher than those of WT mice. These date suggest that ATla play a pivotal role in allergic airway inflammation via, at least in part, the downregulation of Th2 cytokine expression

Differential ER exit in yeast and mammalian cells

The coat complex COPII forms vesicles at the endoplasmic reticulum to transport a variety of cargo proteins to the Golgi structure. Recent biochemical and structural studies reveal the molecular mechanism of cargo protein recognition by COPII components. Furthermore, there are at least two distinct ER-to-Golgi transport carrier structures carrying different cargo proteins in yeast and mammalian cells, suggesting several distinct mechanisms for the concentration, selection and exit of cargo proteins from the ER. It will be essential to follow the dynamics of transitional ER sites and cargo protein concentration within the ER in order to understand how these transport processes occur in living cells

Sphingolipids are required for the stable membrane association of glycosylphosphatidylinositol-anchored proteins in yeast

Ongoing sphingolipid synthesis is specifically required in vivo for the endoplasmic reticulum (ER) to Golgi transport of glycosylphosphatidylinositol (GPI)-anchored proteins. However, the sphingolipid intermediates that are required for transport nor their role(s) have been indentified. Using stereoisomers of dihydrosphingosine, together with specific inhibitors and a mutant defective for sphingolipid synthesis, we now show that ceramides and/or inositol sphingolipids are indispensable for GPI-anchored protein transport. Furthermore, in the absence of sphingolipid synthesis, a significant fraction of GPI-anchored proteins is no longer associated tightly with the ER membrane. The loose membrane association is neither because of the lack of a GPI-anchor nor because of prolonged ER retention of GPI-anchored proteins. These results indicate that ceramides and/or inositol sphingolipids are required to stabilize the association of GPI-anchored proteins with membranes. They could act either by direct involvement as membrane components or as substrates for the remodeling of GPI liquid moieties.</p