Cross-specificity of protective human antibodies against Klebsiella pneumoniae LPS O-antigen.

Humoral immune responses to microbial polysaccharide surface antigens can prevent bacterial infection but are typically strain specific and fail to mediate broad protection against different serotypes. Here we describe a panel of affinity-matured monoclonal human antibodies from peripheral blood immunoglobulin M-positive (IgM+) and IgA+ memory B cells and clonally related intestinal plasmablasts, directed against the lipopolysaccharide (LPS) O-antigen of Klebsiella pneumoniae, an opportunistic pathogen and major cause of antibiotic-resistant nosocomial infections. The antibodies showed distinct patterns of in vivo cross-specificity and protection against different clinically relevant K. pneumoniae serotypes. However, cross-specificity was not limited to K. pneumoniae, as K. pneumoniae-specific antibodies recognized diverse intestinal microbes and neutralized not only K. pneumoniae LPS but also non-K. pneumoniae LPS. Our data suggest that the recognition of minimal glycan epitopes abundantly expressed on microbial surfaces might serve as an efficient humoral immunological mechanism to control invading pathogens and the large diversity of the human microbiota with a limited set of cross-specific antibodies.

Both clades of the epidemic KPC-producing Klebsiella pneumoniae clone ST258 share a modified galactan O-antigen type.

Klebsiella pneumoniae ST258 is a globally disseminated, extremely drug resistant, nosocomial clone with limited treatment options. We show that the vast majority of ST258 isolates express modified d-galactan-I lipopolysaccharide O-antigen, termed hereinafter as D-galactan-III. The genetic determinant required for galactan-III synthesis was identified as a distinct operon adjacent to the rfb (wb) locus encoding D-galactan-I synthesis. The three genes within the operon encode predicted glycosyltransferases. Testing an isogenic transformant pair revealed that expression of D-galactan-III, in comparison to D-galactan-I, conferred improved survival in the presence of human serum. Eighty-three percent of the more than 200 ST258 draft genome sequences currently available carries the corresponding operon and hence these isolates are predicted to express galactan-III antigens. A D-galactan-III specific monoclonal antibody (mAb) was shown to bind to extracted LPS from a panel of ST258 isolates. The same mAb confirmed accessibility of galactan-III in surface staining of ST258 irrespective of the distinct capsular antigens expressed by both clades described previously. Based on these data, the galactan-III antigen may represent an attractive target for active and passive immunization approaches against K. pneumoniae ST258.

Behavioral phenotyping of mice lacking the deubiquitinase USP2.

Ubiquitin specific peptidase 2 (USP2) is a deubiquitinating enzyme expressed almost ubiquitously in the body, including in multiple brain regions. We previously showed that mice lacking USP2 present altered locomotor activity rhythms and response of the clock to light. However, the possible implication of USP2 in regulating other behaviors has yet to be tested. To address this, we ran a battery of behavioral tests on Usp2 KO mice. Firstly, we confirmed our prior findings of increased daily activity and reduced activity fragmentation in Usp2 KO mice. Further, mice lacking USP2 showed impaired motor coordination and equilibrium, a decrease in anxiety-like behavior, a deficit in working memory and in sensorimotor gating. On the other hand, no effects of Usp2 gene deletion were found on spatial memory. Hence, our data uncover the implication of USP2 in different behaviors and expands the range of the known functions of this deubiquitinase.

Identification of d-Galactan-III As Part of the Lipopolysaccharide of Klebsiella pneumoniae Serotype O1.

Klebsiella pneumoniae is a Gram-negative, ubiquitous bacterium capable of causing severe nosocomial infections in individuals with impaired immune system. Emerging multi-drug resistant strains of this species and particularly carbapenem-resistant strains pose an urgent threat to public health. The lipopolysaccharide (LPS) O-antigen is the main surface antigen. It contributes to the virulence of this species and determines the O-serotype of K. pneumoniae isolates. Among the nine main O-serotypes of K. pneumoniae, O1-and O2-type pathogens are causative agents of over 50% of all infections. Serotype O1, the most common O-serotype, expresses complex LPS consisting of d-galactan-I (a polymer built of → 3)-ß-d-Galf-(1 → 3)-α-d-Galp-(1 → repeating units) capped by d-galactan-II (built of [ → 3)-α-d-Galp-(1 → 3)-ß-d-Galp-(1 →] repeating units). Galactan-I is present as the sole polymer in O2 serotype. Recently, in case of serotype O2, conversion of galactan-I to galactan-III (→ 3)-ß-d-Galf-(1 → 3)-[α-d-Galp-(1 → 4)]-α-d-Galp-(1 →) was reported. Substitution of → 3)-α-d-Galp by a branching terminal α-d-Galp was dependent on the presence of the gmlABC operon and had a major impact on the antigenicity of the galactan polymer. Genetic analysis indicated that 40% of the O1 clinical isolates also carry the gmlABC locus; therefore we aimed to characterize the corresponding phenotype of LPS O-antigens. The presence of galactan-III among O1 strains was proven using galactan-III-specific monoclonal antibodies and confirmed by structural analyses performed using sugar and methylation analysis as well as classical and high-resolution magic angle spinning NMR spectroscopy. By using an isogenic mutant pair, we demonstrated that galactan-III expression was dependent on the presence of glycosyltransferases encoded by gmlABC, as was shown previously for the O2 serotype. Furthermore, the galactan-II structures in O1gml+ strains remained unaffected corroborating no functional interactions between the biosynthesis of galactan-III and galactan-II polymers.

Discovery of monoclonal antibodies cross-reactive to novel subserotypes of K. pneumoniae O3.

Klebsiella pneumoniae is responsible for nosocomial infections causing significant morbidity and mortality. Treatment of newly emerging multi-drug resistant strains is hampered due to severely limited antibiotic choices. Passive immunization targeting LPS O-antigens has been proposed as an alternative therapeutic option, given the limited variability of Klebsiella O-antigens. Here we report that the O3 serogroup, previously considered to have uniform O-antigen built of mannan, represents three different subtypes differing in the number of mannose residues within the O-antigen repeating units. Genetic analysis of the genes encoding mannose polymerization revealed differences that underline the observed structural alterations. The O3 variants represent antigenically different types based on the different reactivity pattern of murine monoclonal antibodies raised against a K. pneumoniae O3 strain. Typing of a collection of K. pneumoniae O3 clinical isolates showed that strains expressing the novel O3b antigen, the tri-mannose form, were more prevalent than those having the penta-mannose form, traditionally called O3, while the tetra-mannose variant, termed here O3a, seems to be rare. A monoclonal antibody cross-reacting with all three O3 sub-serogroups was also selected and shown to bind to the surface of various K. pneumoniae strains expressing different O3 subtypes and capsular antigens.

The O-antigen of Plesiomonas shigelloides serotype O36 containing pseudaminic acid.

The structure of the repeating unit of O-antigen of Plesiomonas shigelloides serotype O36 has been investigated by 1H and 13C NMR spectroscopy, matrix-assisted laser-desorption/ionization time-of-flight mass spectrometry and chemical methods. The new structure of trisaccharide has been established: [Formula: see text] These trisaccharide O-antigen units substitute the core undecasaccharide at C-4 of the ß-D-GlcpNAc residue. The core oligosaccharide and lipid A are identical with these of the serotype O17 (PCM 2231) (Maciejewska, A., Lukasiewicz, J., Kaszowska, M., Jachymek, W., Man-Kupisinska, A.; Lugowski, C. Mar. Drugs.2013, 11 (2), 440-454; Lukasiewicz, J., Dzieciatkowska, M., Niedziela, T., Jachymek, W., Augustyniuk, A., Kenne, L., Lugowski, C. Biochemistry, 2006, 45, 10434-10447).

Constant light uncovers behavioral effects of a mutation in the schizophrenia risk gene Dtnbp1 in mice.

Various psychiatric disorders, including schizophrenia, are comorbid with sleep and circadian rhythm disruptions. To understand the links between circadian rhythms and schizophrenia, we analyzed wheel-running behavior of Sandy (Sdy) mice, which have a loss-of-function mutation in the schizophrenia risk gene Dtnbp1, and exhibit several behavioral features of schizophrenia. While rhythms of Sdy mice were mainly normal under light-dark conditions (LD) or in constant darkness (DD), they had a significantly longer free-running period under constant light (LL) compared to wild-type (WT) littermates. The mutant mice also had a higher subjective day/subjective night ratio of activity under LL, indicating lower amplitude, and a lower precision of their onsets of activity under all three lighting conditions. These observations are reminiscent of the circadian disruptions observed in schizophrenia patients. This prompted us to assess schizophrenia-relevant behavioral abnormalities in Sdy mice following alteration of the circadian rhythms by presentation of constant light. Spontaneous locomotor activity, prepulse inhibition (PPI) of acoustic startle and anxiety-like behavior were assessed under baseline LD conditions, then in LL, and then again in LD. Under LL, the Sdy mice showed significantly increased spontaneous locomotion as well as deficits in PPI compared to WT mice. Strikingly, these behavioral deficits persisted even after the mice were returned in LD conditions. While LL led to an increase in anxiety-like behavior in WT animals that was fully reversed after 3 weeks in LD, this effect was not observed in the Sdy mutants. Overall, these results suggest that Dtnbp1 deficiency may lead to increased vulnerability to schizophrenia under environmental conditions where circadian rhythms are altered.

A central role for ubiquitination within a circadian clock protein modification code.

Circadian rhythms, endogenous cycles of about 24 h in physiology, are generated by a master clock located in the suprachiasmatic nucleus of the hypothalamus and other clocks located in the brain and peripheral tissues. Circadian disruption is known to increase the incidence of various illnesses, such as mental disorders, metabolic syndrome, and cancer. At the molecular level, periodicity is established by a set of clock genes via autoregulatory translation-transcription feedback loops. This clock mechanism is regulated by post-translational modifications such as phosphorylation and ubiquitination, which set the pace of the clock. Ubiquitination in particular has been found to regulate the stability of core clock components but also other clock protein functions. Mutation of genes encoding ubiquitin ligases can cause either elongation or shortening of the endogenous circadian period. Recent research has also started to uncover roles for deubiquitination in the molecular clockwork. Here, we review the role of the ubiquitin pathway in regulating the circadian clock and we propose that ubiquitination is a key element in a clock protein modification code that orchestrates clock mechanisms and circadian behavior over the daily cycle.