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► The crystal structure of the title compound was determined. ► A strong H-bond between H(O)3 and a carbonyl of DMM was observed. ► The structures were optimized by five different DFT ...methods. ► High correlation between crystal and calculated geometries was found.
The crystal structure of methyl 6-O-benzyl-2-deoxy-2-dimethylmaleimido-α-d-allopyranoside was solved in order to gain insight into the hydrogen bond features which can be determining features in the glycosylation regioselectivity observed for this compound. An intramolecular hydrogen bond between the hydroxyl H(O)3 and a carbonyl oxygen from the dimethylmaleoyl (DMM) group was observed. This was in agreement with previous NMR temperature shift determinations and molecular modeling. The determination has also found an intermolecular hydrogen bond between the second hydroxyl H(O)4 and the other carbonyl oxygen (generated by symmetry) from DMM. The crystal structure was optimized by five different functionals, namely the hybrid methods B3LYP, M06-2X, B3PW91, and PBE0, and the pure functional PBE, and the optimized geometries were compared with the crystal geometry and with MM3. An excellent coincidence of the geometries was found with the five quantum methods, with minor details deviating from this coincidence. PBE tends to yield larger bond distances, whereas M06-2X fails slightly to match the exocyclic torsion angles for the sugar moiety. In any case, the differences are small, implying that any of these functionals can accurately emulate the geometries of a complex carbohydrate derivative like this one.
Four isomeric
N-dimethylmaleoyl 4,6-
O-benzylidene-protected
d-hexosamine acceptors (
2,
3,
4, and
5) with all possible configurations at C-1 and C-3 (e.g., derived from
d-glucosamine and
...d-allosamine) were prepared, and the assessment of their O-3 relative reactivity through competition experiments using the known per-O-acetylated
d-galactopyranosyl trichloroacetimidate donor (
15) was then carried out. The reactivities are in the order
4
≫
2
>
5
>
3. The analysis of the NMR spectra of
2–5 at different temperature and modeling experiments carried out on analogs of
2–
5 (DFT) and on the acceptors themselves (MM) are coincident, and have helped to establish the stability of the different hydrogen bonds, and of the conformers which carry them. The whole results suggest that the electronic effects (hydrogen bonds) are required to explain the observed trend, in spite of the axial conformation of the most reactive hydroxyl group. The steric effects appear only when hydrogen bonds are weak.
During maturation, reticulocytes lose some membrane proteins that are not required on the mature red cell surface. The proteins are released into the extracellular medium associated with vesicles ...that are formed by budding of the endosomal membrane into the lumen of the compartment; this process results in the formation of multivesicular bodies (MVBs). Fusion of MVBs with the plasma membrane results in secretion of the small internal vesicles, termed exosomes. K562 cells release exosomes with similar characteristics to reticulocyte exosomes, in particular the transferrin receptor (TfR) is found associated with the vesicles. Interestingly, this cell line has been shown to possess high amounts of Rab11 compared with other Rab proteins. To assess the regulation of transferrin receptor release via exosome secretion by Rab11 in this cell type, K562 cells were stably transfected with GFP-Rab11wt or the GTP- and GDP-locked mutants. The distribution of the proteins was assessed by fluorescence microscopy. Transferrin recycling and the number of TfRs present on the surface of the transfected cells were reduced by overexpression of either Rab11wt or the mutants. The amount of released exosomes was analyzed by measuring different molecular markers present on these vesicles either biochemically or by western blot. Overexpression of the dominant-negative mutant Rab11S25N inhibited exosome release, whereas the secretion of exosomes was slightly stimulated in cells transfected with Rab11wt. Taken together, the results demonstrate that in K562 cells Rab11 modulates the exosome pathway although the exact step involved is still not known.
Apoptotic cells have long been considered as intrinsically tolerogenic or unable to elicit immune responses specific for dead cell-associated antigens. However, multiple stimuli can trigger a ...functionally peculiar type of apoptotic demise that does not go unnoticed by the adaptive arm of the immune system, which we named "immunogenic cell death" (ICD). ICD is preceded or accompanied by the emission of a series of immunostimulatory damage-associated molecular patterns (DAMPs) in a precise spatiotemporal configuration. Several anticancer agents that have been successfully employed in the clinic for decades, including various chemotherapeutics and radiotherapy, can elicit ICD. Moreover, defects in the components that underlie the capacity of the immune system to perceive cell death as immunogenic negatively influence disease outcome among cancer patients treated with ICD inducers. Thus, ICD has profound clinical and therapeutic implications. Unfortunately, the gold-standard approach to detect ICD relies on vaccination experiments involving immunocompetent murine models and syngeneic cancer cells, an approach that is incompatible with large screening campaigns. Here, we outline strategies conceived to detect surrogate markers of ICD in vitro and to screen large chemical libraries for putative ICD inducers, based on a high-content, high-throughput platform that we recently developed. Such a platform allows for the detection of multiple DAMPs, like cell surface-exposed calreticulin, extracellular ATP and high mobility group box 1 (HMGB1), and/or the processes that underlie their emission, such as endoplasmic reticulum stress, autophagy and necrotic plasma membrane permeabilization. We surmise that this technology will facilitate the development of next-generation anticancer regimens, which kill malignant cells and simultaneously convert them into a cancer-specific therapeutic vaccine.
Vibrio cholerae is the causative agent of cholera in humans. In addition to the critical virulence factors cholera toxin and toxin co-regulated pilus, V. cholerae secretes V. cholerae cytolysin ...(VCC), a pore-forming exotoxin able to induce cell lysis and extensive vacuolation. We have shown that this vacuolation is related to the activation of autophagy in response to VCC action. Furthermore, we found that the autophagic pathway was required to protect cells upon VCC intoxication. Based on additional data presented here, we propose a model aimed to explain the mechanism of cell protection. We postulate that VCC-induced autophagic vacuoles, which display features of multivesicular bodies and enclose the toxin, are implicated in cell defense through VCC degradation involving fusion with lysosomes.
Addendum to:
Protective Role of Autophagy Against Vibrio cholerae Cytolysin, a Pore-Forming Toxin from V. cholerae
M.G. Gutierrez, H.A. Saka, I. Chinen, F.C.M. Zoppino, T. Yoshimori, J.L. Bocco and M.I. Colombo
Proc Natl Acad Sci USA 2007; 104:1829-34
Studies have been conducted to investigate the reactivity of several bicyclic δ-hydroxynitriles with triflic anhydride in dichloromethane. The reactions of the analogues derived from 1-indanone and ...1-tetralone lead to annulated enones. These products arise from an initial elimination reaction that generates an alkene, followed by the addition of the carbon−carbon double bond to the activated cyano group. The intramolecular cyclization of the derivative obtained from 1-benzosuberone unexpectedly followed a different path, giving a cyclic imidate as the major product. In this case, the activated cyano group is directly attacked by the hydroxyl group of the starting δ-hydroxynitrile. Theoretical calculations provide a rationale for the observed reactivity pattern. Both the formation of the triflate via its protonated form, its subsequent ionization to the carbocation, and the cyclization of the resulting alkene to the enone become less favorable when the size of the ring increases due to conformational effects. The opposite trend is observed for the competing Pinner-type cyclization to the imidate. An alternative mechanism for the formation of the lactams from the cyclic imidates under acid-catalyzed conditions has also been proposed.
The water-hyacinth grasshopper, Cornops aquaticum, occurs in freshwater environments in the New World between latitudes 23°N and 35°S. At the southernmost margin of this distribution the populations ...are polymorphic for three centric fusions (Robertsonian translocations). The frequencies of these chromosome rearrangements increase southwards and the recombination in structural homozygotes and heterozygotes diminishes both along the middle and lower courses of the Paraná River. In the present paper we report a similar cline along the southward flowing Uruguay River. In addition, we report the morphological effects of two of these centric fusion polymorphisms, namely the fusions between chromosomes 2 and 5 of the standard complement (fusion 2/5) and chromosomes 3 and 4 (fusion 3/4) and extend this study to the Uruguay River. There is a strong inverse correlation of fusion frequency with temperature, which indicates that these polymorphisms may be related to increased tolerance of colder climates in this originally tropical species, or some other correlated variable. This study is a further example of chromosomal clines correlated with latitude and is one of a few examples of chromosome polymorphisms associated with phenotypic effects. Finally, it indicates ways of using this species for controlling pests.
An assessment of the relative O-3/O-4 reactivities of both methyl α- and β-
d-glycosides of
N-dimethylmaleoyl (DMM)
d-glucosamine acceptors protected at O-6 with benzoyl (Bz), benzyl (Bn), and
...tert-butyldiphenylsilyl (TBDPS) groups is presented using per-O-benzoylated β-
d-galactofuranosyl and per-O-acetylated α-
d-galactopyranosyl trichloroacetimidates as glycosyl donors. Using the former donor, the α anomer of the 6-O-benzoylated compound gave exclusive substitution at O-3, whereas the other two compounds with α-configuration kept this site as preferential. The β anomer of the 6-O-benzoylated compound gave the same amounts of reaction products on O-3 and O-4, whereas the other β analogs carried a more reactive O-4. The same reactions were carried out using as donor the less-reactive per-O-acetylated α-
d-galactopyranosyl trichloroacetimidate. Although the same trend was found to occur, the O-4 was always relatively more reactive with the pyranosyl donor than with the furanosyl donor, when keeping the remaining factors constant. Furthermore, the β anomers of the acceptor gave almost exclusive substitution at O-4. These observations confirm and extend the utility of these ‘matching’ donor and acceptor reactivities.
In a previous paper (Bohn et al., Carbohydr. Res., 2007, 342, 2522) the relative O3/O4 reactivities of both alpha- and beta-methyl glycosides of N-dimethylmaleoyl (DMM) glucosamine acceptors ...protected at O6 with three different groups were assessed by us, using two glycosyl donors. The alpha-anomers showed preferential or exclusive substitution at O3, whereas the beta-anomers gave preferential or exclusive substitution at O4. A DFT study of analogs of the reported acceptors indicates that whereas the beta-anomers carry the DMM ring parallel to the C2-H2 bond for steric reasons, the alpha-anomers tilt this ring producing a strong hydrogen bond between the H(O)3 and one of the DMM carbonyl groups. In this way, the O3 group becomes more nucleophilic and thus more reactive: both charge and Fukui functions on O3 and O4 in the model compounds support the experimental results. Surprisingly, the previously mentioned hydrogen bond is not the only driving force for the slant of the DMM group: the axial methoxyl group of the alpha-anomers also plays a role. The ease of rotation around the C2-N2 bond for DMM-protected analogs was assessed with different models. MP2 calculations using higher basis sets yield similar relative energy and charge values to those calculated using DFT.
Autophagy is involved in several physiological and pathological processes. One of the key roles of the autophagic pathway is to participate in the first line of defense against the invasion of ...pathogens, as part of the innate immune response. Targeting of intracellular bacteria by the autophagic machinery, either in the cytoplasm or within vacuolar compartments, helps to control bacterial proliferation in the host cell, controlling also the spreading of the infection. In this review we will describe the means used by diverse bacterial pathogens to survive intracellularly and how they are recognized by the autophagic molecular machinery, as well as the mechanisms used to avoid autophagic clearance.
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