Characterization of functional oligosaccharide mimics of the Shigella flexneri serotype 2a O-antigen: implications for the development of a chemically defined glycoconjugate vaccine

Protection against reinfection with noncapsulated Gram-negative bacteria, such as Shigella, an enteroinvasive bacterium responsible for bacillary dysentery, is mainly achieved by Abs specific for the O-Ag, the polysaccharide part of the LPS, the major bacterial surface Ag. The use of chemically defined glycoconjugates encompassing oligosaccharides mimicking the protective determinants carried by the O-Ag, thus expected to induce an efficient anti-LPS Ab response, has been considered an alternative to detoxified LPS-protein conjugate vaccines. The aim of this study was to identify such functional oligosaccharide mimics of the S. flexneri serotype 2a O-Ag. Using protective murine mAbs specific for S. flexneri serotype 2a and synthetic oligosaccharides designed to analyze the contribution of each sugar residue of the branched pentasaccharide repeating unit of the O-Ag, we demonstrated that the O-Ag exhibited an immunodominant serotype-specific determinant. We also showed that elongating the oligosaccharide sequence improved Ab recognition. From these antigenicity data, selected synthetic oligosaccharides were assessed for their potential to mimic the O-Ag by analyzing their immunogenicity in mice when coupled to tetanus toxoid via single point attachment. Our results demonstrated that induction of an efficient serotype 2a-specific anti-O-Ag Ab response was dependent on the length of the oligosaccharide sequence. A pentadecasaccharide representing three biological repeating units was identified as a potential candidate for further development of a chemically defined glycoconjugate vaccine against S. flexneri 2a infection.     

The Doubly Phosphorylated Form of HPr, HPr(Ser-P)(His～P), Is Abundant in Exponentially Growing Cells of Streptococcus thermophilus and Phosphorylates the Lactose Transporter LacS as Efficiently as HPr(His～P)

In Streptococcus thermophilus, lactose is taken up by LacS, a transporter that comprises a membrane translocator domain and a hydrophilic regulatory domain homologous to the IIA proteins and protein domains of the phosphoenolpyruvate:sugar phosphotransferase system (PTS). The IIA domain of LacS (IIA^LacS) possesses a histidine residue that can be phosphorylated by HPr(His~P), a protein component of the PTS. However, determination of the cellular levels of the different forms of HPr, namely, HPr, HPr(His~P), HPr(Ser-P), and HPr(Ser-P)(His~P), in exponentially lactose-growing cells revealed that the doubly phosphorylated form of HPr represented 75% and 25% of the total HPr in S. thermophilus ATCC 19258 and S. thermophilus SMQ-301, respectively. Experiments conducted with [³²P]PEP and purified recombinant S. thermophilus ATCC 19258 proteins (EI, HPr, and IIA^LacS) showed that IIA^LacS was reversibly phosphorylated by HPr(Ser-P)(His~P) at a rate similar to that measured with HPr(His~P). Sequence analysis of the IIA^LacS protein domains from several S. thermophilus strains indicated that they can be divided into two groups on the basis of their amino acid sequences. The amino acid sequence of IIA^LacS from group I, to which strain 19258 belongs, differed from that of group II at 11 to 12 positions. To ascertain whether IIA^LacS from group II could also be phosphorylated by HPr(His~P) and HPr(Ser-P)(His~P), in vitro phosphorylation experiments were conducted with purified proteins from Streptococcus salivarius ATCC 25975, which possesses a IIA^LacS very similar to group II S. thermophilus IIA^LacS. The results indicated that S. salivarius IIA^LacS was phosphorylated by HPr(Ser-P)(His~P) at a higher rate than that observed with HPr(His~P). Our results suggest that the reversible phosphorylation of IIA^LacS in S. thermophilus is accomplished by HPr(Ser-P)(His~P) as well as by HPr(His~P).     

Jumping the barrier: VE-cadherin, VEGF and other angiogenic modifiers in cancer

The endothelial barrier controls the passage of fluids, nutrients and cells through the vascular wall. This physiological function is closely related to developmental and adult angiogenesis, blood pressure control, as well as immune responses. Moreover, cancer progression is frequently characterized by disorganized and leaky blood vessels. In this context, vascular permeability drives tumour-induced angiogenesis, blood flow disturbances, inflammatory cell infiltration and tumour cell extravasation. Although various molecules have been implicated, the vascular endothelial adhesion molecule, VE-cadherin (vascular endothelial cadherin), has emerged as a critical player involved in maintaining endothelial barrier integrity and homoeostasis. Indeed, VE-cadherin coordinates the endothelial cell-cell junctions through its adhesive and signalling properties. Of note, many angiogenic and inflammatory mediators released into the tumour microenvironment influence VE-cadherin behaviour. Therefore restoring VE-cadherin function could be one very promising target for vascular normalization in cancer therapies. In this review, we will mainly focus on recent discoveries concerning the molecular mechanisms involved in modulating VE-cadherin plasticity in cancer.     

Towards an in vitro model of Plasmodium hypnozoites suitable for drug discovery

Background

Amongst the Plasmodium species in humans, only P. vivax and P. ovale produce latent hepatic stages called hypnozoites, which are responsible for malaria episodes long after a mosquito bite. Relapses contribute to increased morbidity, and complicate malaria elimination programs. A single drug effective against hypnozoites, primaquine, is available, but its deployment is curtailed by its haemolytic potential in glucose-6-phosphate dehydrogenase deficient persons. Novel compounds are thus urgently needed to replace primaquine. Discovery of compounds active against hypnozoites is restricted to the in vivo P. cynomolgi-rhesus monkey model. Slow growing hepatic parasites reminiscent of hypnozoites had been noted in cultured P. vivax-infected hepatoma cells, but similar forms are also observed in vitro by other species including P. falciparum that do not produce hypnozoites.

Methodology

P. falciparum or P. cynomolgi sporozoites were used to infect human or Macaca fascicularis primary hepatocytes, respectively. The susceptibility of the slow and normally growing hepatic forms obtained in vitro to three antimalarial drugs, one active against hepatic forms including hypnozoites and two only against the growing forms, was measured.

Results

The non-dividing slow growing P. cynomolgi hepatic forms, observed in vitro in primary hepatocytes from the natural host Macaca fascicularis, can be distinguished from similar forms seen in P. falciparum-infected human primary hepatocytes by the differential action of selected anti-malarial drugs. Whereas atovaquone and pyrimethamine are active on all the dividing hepatic forms observed, the P. cynomolgi slow growing forms are highly resistant to treatment by these drugs, but remain susceptible to primaquine.

Conclusion

Resistance of the non-dividing P. cynomolgi forms to atovaquone and pyrimethamine, which do not prevent relapses, strongly suggests that these slow growing forms are hypnozoites. This represents a first step towards the development of a practical medium-throughput in vitro screening assay for novel hypnozoiticidal drugs.     

Classification of ancient mammal individuals using dental pulp MALDI-TOF MS peptide profiling

Background

The classification of ancient animal corpses at the species level remains a challenging task for forensic scientists and anthropologists. Severe damage and mixed, tiny pieces originating from several skeletons may render morphological classification virtually impossible. Standard approaches are based on sequencing mitochondrial and nuclear targets.

Methodology/Principal Findings

We present a method that can accurately classify mammalian species using dental pulp and mass spectrometry peptide profiling. Our work was organized into three successive steps. First, after extracting proteins from the dental pulp collected from 37 modern individuals representing 13 mammalian species, trypsin-digested peptides were used for matrix-assisted laser desorption/ionization time-of-flight mass spectrometry analysis. The resulting peptide profiles accurately classified every individual at the species level in agreement with parallel cytochrome b gene sequencing gold standard. Second, using a 279–modern spectrum database, we blindly classified 33 of 37 teeth collected in 37 modern individuals (89.1%). Third, we classified 10 of 18 teeth (56%) collected in 15 ancient individuals representing five mammal species including human, from five burial sites dating back 8,500 years. Further comparison with an upgraded database comprising ancient specimen profiles yielded 100% classification in ancient teeth. Peptide sequencing yield 4 and 16 different non-keratin proteins including collagen (alpha-1 type I and alpha-2 type I) in human ancient and modern dental pulp, respectively.

Conclusions/Significance

Mass spectrometry peptide profiling of the dental pulp is a new approach that can be added to the arsenal of species classification tools for forensics and anthropology as a complementary method to DNA sequencing. The dental pulp is a new source for collagen and other proteins for the species classification of modern and ancient mammal individuals.     

Effects of backbone substitutions on the conformational behavior of Shigella flexneri O-antigens: implications for vaccine strategy

The O-antigen (O-Ag), the polysaccharide part of the lipopolysaccharide, is the major target of the serotype-specific protective humoral response elicited upon host infection by Shigella flexneri, the main causal agent of the endemic form of bacillary dysentery. The O-Ag repeat units (RUs) of 12 S. flexneri serotypes share the tetrasaccharide backbone →2)-α-l-Rhap-(1?→?2)-α-l-Rhap-(1?→?3)-α-l-Rhap-(1?→?3)-β-d-GlcpNAc-(1→, with site-selective glucosylation(s) and/or O-acetylation defining the serotypes. To investigate the conformational basis of serotype specificity, we sampled conformational behaviors during 60?ns of molecular dynamic simulations for oligosaccharides representing three RUs of each one of the O-Ags corresponding to serotypes 1a, 1b, 2a, 2b, 3a, 3b, 4a, 4b, 5a, 5b, X and Y, respectively. The calculated trajectories were checked by nuclear magnetic resonance (NMR) for 1a, 2a, 3a and 5a O-Ags. The simulations predict that in all O-Ags, but 1a and 1b, serotype-specific substitutions of the backbone do not induce any new backbone conformations compared with the linear type O-Ag Y, although they restrain locally the accessible conformational space. Moreover, the influence of any given substituent on the backbone is independent of the eventual presence of other substituents. Finally, only slight differences in conformational behavior between terminal and inner RUs were observed. These results suggest that the reported serotype-specificity of the protective immune response is not due to recognition of distinct backbone conformations, but to binding of the serotype-defining substituents in the O-Ag context. The gained knowledge is discussed in terms of impact on the development of a broad-serotype coverage vaccine.     

Breast fine-needle aspiration malondialdehyde deoxyguanosine adduct in breast cancer

This study has analysed the generation of 3-(2-deoxy-β-D-erythro-pentafuranosyl)pyrimido[1,2-α]purin-10(3H)-one deoxyguanosine adduct [M?dG], a biomarker of oxidative stress and lipid peroxidation, in breast fine-needle aspirate samples of 22 patients with breast cancer, at different clinical stages, in respect to 13 controls. The multivariate analysis show that M(1)dG adduct was higher in cases than in controls (Mean Ratio (MR) = 5.26, 95% CI = 3.16-8.77). Increased M?dG was observed in women with a tumour grade 3 and a pathological diameter 2 (MR = 7.61, 95% CI = 3.91-14.80 and MR = 5.75, 95% CI = 3.13-10.59, respectively). A trend with increasing tumour grade and pathological diameter was present (MR = 1.98, 95% CI = 1.57-2.50 and MR = 2.44, 95% CI = 1.71-3.48, respectively). Not significant effects of age and smoking habit were found (MR = 1.58, 95% CI = 0.92-2.72 and MR = 1.68, 95% CI 0.88-3.20, respectively). An increment over the background frequency of M?dG can contribute to breast cancer development. Increasing severity of breast tumour can influence DNA damage level.     

Plant ALDH10 Family: IDENTIFYING CRITICAL RESIDUES FOR SUBSTRATE SPECIFICITY AND TRAPPING A THIOHEMIACETAL INTERMEDIATE*

Plant ALDH10 family members are aminoaldehyde dehydrogenases (AMADHs), which oxidize ω-aminoaldehydes to the corresponding acids. They have been linked to polyamine catabolism, osmoprotection, secondary metabolism (fragrance), and carnitine biosynthesis. Plants commonly contain two AMADH isoenzymes. We previously studied the substrate specificity of two AMADH isoforms from peas (PsAMADHs). Here, two isoenzymes from tomato (Solanum lycopersicum), SlAMADHs, and three AMADHs from maize (Zea mays), ZmAMADHs, were kinetically investigated to obtain further clues to the catalytic mechanism and the substrate specificity. We also solved the high resolution crystal structures of SlAMADH1 and ZmAMADH1a because these enzymes stand out from the others regarding their activity. From the structural and kinetic analysis, we can state that five residues at positions 163, 288, 289, 444, and 454 (PsAMADHs numbering) can, directly or not, significantly modulate AMADH substrate specificity. In the SlAMADH1 structure, a PEG aldehyde derived from the precipitant forms a thiohemiacetal intermediate, never observed so far. Its absence in the SlAMADH1-E260A structure suggests that Glu-260 can activate the catalytic cysteine as a nucleophile. We show that the five AMADHs studied here are capable of oxidizing 3-dimethylsulfoniopropionaldehyde to the cryo- and osmoprotectant 3-dimethylsulfoniopropionate. For the first time, we also show that 3-acetamidopropionaldehyde, the third aminoaldehyde besides 3-aminopropionaldehyde and 4-aminobutyraldehyde, is generally oxidized by AMADHs, meaning that these enzymes are unique in metabolizing and detoxifying aldehyde products of polyamine degradation to nontoxic amino acids. Finally, gene expression profiles in maize indicate that AMADHs might be important for controlling ω-aminoaldehyde levels during early stages of the seed development.