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Biomedical subjects

Ulrich Baumann

Publications and source records attributed to Ulrich Baumann.

At least 19 recordsLinked to original sources
PubMed2026

Human GPR174 deficiency drives polyclonal lymphoproliferative disease via defects in T cell function.

The X-linked G-protein coupled receptor GPR174 is highly expressed in T and B lymphocytes and has immunoregulatory roles in mice, but its function in humans is unknown. We describe a cohort of six individuals who have function-disrupting variants in GPR174 and a clinical phenotype of lymphadenopathy and autoimmunity. Histological analysis of two patient lymph nodes revealed necrotizing lymphadenitis and lymphoproliferation resembling Kikuchi-Fujimoto disease. In-depth analysis of three patients and related carriers revealed overaccumulation of CD8 terminally differentiated effector memory cells re-expressing CD45RA (TEMRA). Patient cells and GPR174-deficient CD8 T cells generated from controls showed less repression of proliferation by the GPR174 ligand lysophosphatidylserine (lysoPS) and an effector-biased gene expression program. GPR174-deficient CD4 T cells were resistant to lysoPS-mediated suppression of IL2 production. In mice, chronic viral infection led to over-accumulation of GPR174-deficient effector CD8 T cells. We describe an inborn error of immunity associated with dysregulated lymphocyte responses that we propose predisposes to exaggerated lymphoproliferation and autoimmunity following viral infection.

Journal Article↗
PubMed2006

Substrate specificity of a metalloprotease of the pappalysin family revealed by an inhibitor and a product complex.

Human pappalysin-1 is a multi-domain metalloprotease engaged in the homeostasis of insulin-like growth factors and the founding member of the pappalysin family within the metzincin clan of metalloproteases. We have recently identified an archaeal relative, ulilysin, encompassing only the protease domain. It is a 262-residue active protease with a novel 3D structure with two subdomains separated by an active-site cleft. Despite negligible overall sequence similarity, noticeable similarity is found with other metzincin prototypes, adamalysins/ADAMs and matrix metalloproteinases. Ulilysin has been crystallised in a product complex with an arginine-valine dipeptide occupying the active-site S(1') and S(2') positions and in a complex with the broad-spectrum hydroxamic acid-based metalloprotease inhibitor, batimastat. This molecule inhibits mature ulilysin with an IC(50) value of 61 microM under the conditions assayed. The binding of batimastat to ulilysin evokes binding to vertebrate matrix metalloproteases but is much weaker. These data give insight into substrate specificity and mechanism of action and inhibition of the novel pappalysin family.

Amino Acid Sequence↗
PubMed2006

ICOS deficiency is associated with a severe reduction of CXCR5+CD4 germinal center Th cells.

ICOS is expressed on activated T cells and particularly on CXCR5+ follicular Th cells in germinal centers (GC). Its deletion leads to a profound deficiency in memory B cell formation and switched Ab response in humans. Here, we show that in ICOS-deficient patients the generation of GCs is severely disturbed, and the numbers of circulating CXCR5+CD45RO+ memory CD4 T cells are significantly reduced, indicating an essential role of ICOS in the differentiation of CXCR5+CD4 T cells. The GC-specific CD57+CXCR5+ subpopulation is virtually absent. In ICOS-/- mice, the decrease of circulating CXCR5+CD4 T cells reflects the reduction of CXCR5+ follicular Th cells in lymph nodes and spleen. Therefore, in concurrence with the absence of CXCR5+ T cells in the blood of CD40L-deficient patients, these data support the hypothesis that circulating CD57+CXCR5+ T cells are GC derived and thus may serve as a surrogate marker for the presence of functional GCs in humans.

Animals↗
PubMed2006

Role of inducible nitric oxide synthase and NADPH oxidase in early control of Burkholderia pseudomallei infection in mice.

Infection with the soil bacterium Burkholderia pseudomallei can result in a variety of clinical outcomes, including asymptomatic infection. The initial immune defense mechanisms which might contribute to the various outcomes after environmental contact with B. pseudomallei are largely unknown. We have previously shown that relatively resistant C57BL/6 mice can restrict bacterial B. pseudomallei growth more efficiently within 1 day after infection than highly susceptible BALB/c mice. By using this model, our study aimed to investigate the role of macrophage-mediated effector mechanisms during early B. pseudomallei infection. Depletion of macrophages revealed an essential role of these cells in the early control of infection in BALB/c and C57BL/6 mice. Strikingly, the comparison of the anti-B. pseudomallei activity of bone marrow-derived macrophages (BMM) from C57BL/6 and BALB/c mice revealed an enhanced bactericidal activity of C57BL/6 BMM, particularly after gamma interferon (IFN-gamma) stimulation. In vitro experiments with C57BL/6 gp91phox-/- BMM showed an impaired intracellular killing of B. pseudomallei compared to experiments with wild-type cells, although C57BL/6 gp91phox-/- cells still exhibited substantial killing activity. The anti-B. pseudomallei activity of C57BL/6 iNOS-/- BMM was not impaired. C57BL/6 gp91phox-/- mice lacking a functional NADPH oxidase were more susceptible to infection, whereas C57BL/6 mice lacking inducible nitric oxide synthase (iNOS) did not show increased susceptibility but were slightly more resistant during the early phase of infection. Thus, our data suggest that IFN-gamma-mediated but iNOS-independent anti-B. pseudomallei mechanisms of macrophages might contribute to the enhanced resistance of C57BL/6 mice compared to that of BALB/c mice in the early phase of infection.

Animals↗
PubMed2006

Regulation of the Dha operon of Lactococcus lactis: a deviation from the rule followed by the Tetr family of transcription regulators.

Dihydroxyacetone (Dha) kinases are a novel family of kinases with signaling and metabolic functions. Here we report the x-ray structures of the transcriptional activator DhaS and the coactivator DhaQ and characterize their function. DhaQ is a paralog of the Dha binding Dha kinase subunit; DhaS belongs to the family of TetR repressors although, unlike all known members of this family, it is a transcriptional activator. DhaQ and DhaS form a stable complex that in the presence of Dha activates transcription of the Lactococcus lactis dha operon. Dha covalently binds to DhaQ through a hemiaminal bond with a histidine and thereby induces a conformational change, which is propagated to the surface via a cantilever-like structure. DhaS binding protects an inverted repeat whose sequence is GGACACATN6ATTTGTCC and renders two GC base pairs of the operator DNA hypersensitive to DNase I cleavage. The proximal half-site of the inverted repeat partially overlaps with the predicted -35 consensus sequence of the dha promoter.

Amino Acid Sequence↗
PubMed2006

The crystal structure of the carboxy-terminal domain of human translation initiation factor eIF5.

The carboxy-terminal domain (CTD) of eukaryotic initiation factor 5 (eIF5) plays a central role in the formation of the multifactor complex (MFC), an important intermediate for the 43 S pre-initiation complex assembly. The IF5-CTD interacts directly with the translation initiation factors eIF1, eIF2-beta, and eIF3c, thus forming together with eIF2 bound Met-tRNA(i)(Met) the MFC. In this work we present the high resolution crystal structure of eIF5-CTD. This domain of the protein is exclusively composed out of alpha-helices and is homologous to the carboxy-terminal domain of eIF2B-epsilon (eIF2Bepsilon-CTD). The most striking difference in the two structures is an additional carboxy-terminal helix in eIF5. The binding sites of eIF2-beta, eIF3 and eIF1 were mapped onto the structure. eIF2-beta and eIF3 bind to non-overlapping patches of negative and positive electrostatic potential, respectively.

Amino Acid Sequence↗
PubMed2006

Molecular analysis of ulilysin, the structural prototype of a new family of metzincin metalloproteases.

The metzincin clan encompasses several families of zinc-dependent metalloproteases with proven function both in physiology and pathology. They act either as broad spectrum protein degraders or as sheddases, operating through limited proteolysis. Among the structurally uncharacterized metzincin families are the pappalysins, of which the most thoroughly studied member is human pregnancy-associated plasma protein A (PAPP-A), a heavily glycosylated 170-kDa multidomain protein specifically cleaving insulin-like growth factor (IGF)-binding proteins (IGFBPs). Proulilysin is a 38-kDa archaeal protein that shares sequence similarity with PAPP-A but encompasses only the pro-domain and the catalytic domain. It undergoes calcium-mediated autolytic activation, and the mature protein adopts a three-dimensional structure with two subdomains separated by an active site cleft containing the catalytic zinc ion. This structure is reminiscent of human members of the adamalysin/ADAMs (a disintegrin and a metalloprotease) family of metzincins. A bound dipeptide yields information on the substrate specificity of ulilysin, which specifically hydrolyzes IGFBP-2 to -6, insulin, and extracellular matrix proteins but not IGFBP-1 or IGF-II. Accordingly, ulilysin has higher proteolytic efficiency and a broader substrate specificity than human PAPP-A. The structure of ulilysin represents a prototype for the catalytic domain of pappalysins.

Amino Acid Sequence↗
PubMed2006

Crystal structure of the nucleotide-binding subunit DhaL of the Escherichia coli dihydroxyacetone kinase.

Dihydroxyacetone (Dha) kinases are a family of sequence-related enzymes that utilize either ATP or phosphoenolpyruvate (PEP) as source of high energy phosphate. The PEP-dependent Dha kinase of Escherichia coli consists of three subunits. DhaK and DhaL are homologous to the Dha and nucleotide-binding domains of the ATP-dependent kinase of Citrobacter freundii. The DhaM subunit is a multiphosphorylprotein of the PEP:sugar phosphotransferase system (PTS). DhaL contains a tightly bound ADP as coenzyme that gets transiently phosphorylated in the double displacement of phosphate between DhaM and Dha. Here we report the 2.6A crystal structure of the E.coli DhaL subunit. DhaL folds into an eight-helix barrel of regular up-down topology with a hydrophobic core made up of eight interlocked aromatic residues and a molecule of ADP bound at the narrower end of the barrel. The alpha and beta phosphates of ADP are complexed by two Mg2+ and by a hydrogen bond to the imidazole ring of an invariant histidine. The Mg ions in turn are coordinated by three gamma-carboxyl groups of invariant aspartate residues. Water molecules complete the octahedral coordination sphere. The nucleotide is capped by an alpha-helical segment connecting helices 7 and 8 of the barrel. DhaL and the nucleotide-binding domain of the C.freundii kinase assume the same fold but display strongly different surface potentials. The latter observation and biochemical data indicate that the domains of the C.freundii Dha kinase constitute one cooperative unit and are not randomly interacting and independent like the subunits of the E.coli enzyme.

Adenosine Diphosphate↗
PubMed2006

The molecular architecture of the metalloprotease FtsH.

The ATP-dependent integral membrane protease FtsH is universally conserved in bacteria. Orthologs exist in chloroplasts and mitochondria, where in humans the loss of a close FtsH-homolog causes a form of spastic paraplegia. FtsH plays a crucial role in quality control by degrading unneeded or damaged membrane proteins, but it also targets soluble signaling factors like sigma(32) and lambda-CII. We report here the crystal structure of a soluble FtsH construct that is functional in caseinolytic and ATPase assays. The molecular architecture of this hexameric molecule consists of two rings where the protease domains possess an all-helical fold and form a flat hexagon that is covered by a toroid built by the AAA domains. The active site of the protease classifies FtsH as an Asp-zincin, contrary to a previous report. The different symmetries of protease and AAA rings suggest a possible translocation mechanism of the target polypeptide chain into the interior of the molecule where the proteolytic sites are located.

Adenosine Triphosphatases↗
PubMed2006

The Budd-Chiari syndrome in children: the spectrum of management.

The Budd-Chiari syndrome (BCS), characterized by hepatic venous outflow occlusion, is rare in children. We describe the cases of 3 patients with BCS who presented at different stages of liver dysfunction that required tailored management. A 10-year-old boy who presented with a weeklong history of abdominal discomfort received an early diagnosis. Treatment with thrombolytic therapy and adjunctive percutaneous interventional radiologic management led to a favorable outcome in this patient. A 2-year-old girl referred with a 6-week illness not amenable to thrombolytic therapy was managed with a pericardial patch atriocavoplasty to restore hepatic venous outflow tract patency. The third patient, a 5-year-old girl, presented with established cirrhosis and massive ascites. After we controlled the ascites with an extracorporeal shunt system and nutritional resuscitation, we conducted an orthotopic liver transplantation on this patient. The stage of disease at diagnosis influences the management strategy, and an early diagnosis offers patients the best possible chance of cure without major surgery. However, a later presentation can still be successfully managed by more radical surgical interventions. The aims of this case report were to emphasize the importance of a high index of suspicion in the diagnosis of pediatric BCS and to highlight the importance of early referral to a specialized pediatric liver unit with the necessary facilities to deal with the medical and surgical aspects of management.

Ascites↗
PubMed2006

Lectin-reactive alpha-fetoprotein in patients with tyrosinemia type I and hepatocellular carcinoma.

Despite the introduction of 2-(2-nitro-4-trifluormethyl-benzoyl)-1,3-cyclohexandion into the treatment of hereditary tyrosinemia type I (HT1), patients remain at risk of developing hepatocellular carcinoma (HCC). Serial total alpha-fetoprotein (AFP) levels are used to monitor the individual patient. Lectin-reactive alpha-fetoprotein (L3-AFP) is an AFP isoform that is expressed by malignant liver tumors. We investigated whether the analysis of L3-AFP could lead to earlier detection of HCC in HT1 compared with judgement based on total AFP alone. AFP electrophoresis using lectin-containing agarose gel identifies L3-AFP by the affinity of its specific carbohydrate chain to lectin. We report the retrospective analysis of sequential serum samples of 12 patients with HT1 and histologically proven HCC. AFP isoforms could be identified in all 12 patients. In 6 patients, the L3-AFP increased before the total AFP. In 3 patients, the rise in L3-AFP was parallel to the rise of total AFP; and in 3 patients, the L3-AFP was raised after the total AFP or did not increase at all. We were able to identify 6 of 12 patients with an early increase in the new tumor marker. Lectin-affinity electrophoresis may have a role in discriminating benign liver disease from HCC in HT1. We suggest the further evaluation of L3-AFP in HT1.

Adolescent↗
PubMed2006

Oxidative changes of bronchoalveolar proteins in cystic fibrosis.

Chronic bacterial infection and severe, polymorphonuclear neutrophil-dominated endobronchial inflammation are characteristic hallmarks of cystic fibrosis (CF) lung disease. The free radicals generated can be deleterious for structure and function of many proteins. The goal of this study was to investigate the degree of oxidation of pulmonary epithelial lining fluid proteins. BAL fluid (BALF) from 55 children with CF and from 11 patients in a control group were investigated by dot-blot assay for content and by two-dimensional electrophoresis and Western blotting for the pattern of distribution of oxidized proteins. The highest level of oxidative stress, as assessed by the level of protein carbonyls, was found in patients with FEV1 < 80% of predicted or with highly elevated neutrophil counts. Compared to control subjects without lung disease, CF patients with normal lung function and CF patients with a normal neutrophil count in their BALF had significantly higher protein carbonyl levels. The extent of protein oxidation was directly related to the neutrophil granulocyte count and inversely to lung function. Our data support the hypothesis that oxidative damage of pulmonary proteins during chronic and excessive neutrophilic endobronchial inflammation may contribute to the decline of lung function in CF patients.

Adolescent↗
PubMed2005

Mechanistic study of proton transfer and hysteresis in catalytic antibody 16E7 by site-directed mutagenesis and homology modeling.

Antibody 16E7 catalyzes the carbon protonation of enol ether 2 to hemiacetal 3, and the carbon deprotonation of benzisoxazole 7 to phenol 8. This antibody shows an extreme case of hysteresis, requiring several hours to reach full activity. Antibody 16E7 was expressed as recombinant chimeric Fab in Escherichia coli. A model for the three-dimensional structure was produced by homology modeling and used for a docking procedure to obtain models for antibody-ligand complexes. Site-direct mutagenesis of GluL39, identified as a possible catalytic residue by the model, to either glutamine or alanine abolished catalysis, showing that both the protonation reaction of enol ether 2 and the deprotonation of benzisoxazole 7 are promoted by the same residue. The model furthermore suggested that substrate access to the catalytic site might be hindered by a flexible HCDR3 loop held in closed position by a hydrogen bond between SerH99 and GluL39, which could explain the observed hysteresis effect. In agreement with this model, mutagenesis of SerH99 to alanine, or deletion of this residue, was found to reduce hysteresis by approximately 50%.

Antibodies, Catalytic↗
PubMed2005

Preservation of the synthetic and metabolic capacity of isolated human hepatocytes by coculture with human biliary epithelial cells.

Bioartificial liver support systems have demonstrated limited efficacy in compensation of liver detoxification and substitution of liver-derived factors. However, in these devices, the biological substitution of the complex liver function has been restricted to xenogeneic or transformed hepatocytes. Therefore, we have examined the long-term effect of coculturing normal human hepatocytes (HCs) with allogeneic biliary epithelial cells (BECs). We applied functional in vitro assays to examine their metabolic potential by ammonia detoxification to urea, cytochrome P450-dependent lignocaine conversion to mono-ethyl-glycine-xylidide (MEGX), and protein expression and secretion. As the liver has a pivotal role in the synthesis of coagulation factors, we measured antithrombin III (AT III), factor VII, and albumin, comparing HCs plated on collagen or inside 3-dimensional collagen gels. Over 30 days, expression and secretion of albumin and clotting factors by human HCs were augmented by culture inside collagen gel, but were also enhanced and better maintained by coculture with BECs. Higher proportions of BECs cocultured with HCs substantially increased the protein synthesis and urea production. Remarkably, the almost absent cytochrome P450 activity of HC alone after 1 week could be reversed and maintained over 3 weeks by coculture with BECs. The pattern of these effects differed from the extent of interleukin-6 (IL-6) production and HC viability under the compared conditions. In conclusion, coculture of human HCs with BECs impressively restores the synthetic and metabolic liver function in vitro. These results suggest mechanisms of improved liver epithelial differentiation supported by coculture conditions. This technique offers new perspectives in bioartificial liver support, hepatocyte transplantation, and stem cell differentiation.

Bile Ducts↗
PubMed2005

Removal of metabolites, cytokines and hepatic growth factors by extracorporeal liver support in children.

BACKGROUND: Molecular Adsorbents Recirculating System (MARS)-mini has recently been approved and applied in children with hepatic failure. However, its indication, efficacy and capability to induce liver regeneration remain unclear. The aim of our pilot study in children was to analyse the impact of MARS on markers of detoxification and regeneration. METHODS: In children with fulminant Wilson's disease and bridged with MARSmini for liver transplantation, we analyzed toxic metabolites (bile acids, bilirubin, lactate, ammonia, tryptophan and copper), regulators of the inflammatory cascade [nitrate, tumor necrosis factor-alpha (TNF-alpha), interleukin-6 (IL-6), methionine, cystine and hyaluronic acid] and hepatic growth factors [hepatocyte growth factor (HGF), epidermal growth factor (EGF), transforming growth factor-beta1 (TGF-beta1), cortisol, corticosteroid-binding globulin (CBG), insulin-like growth factor-1 (IGF-1), angiogenin, vascular endothelial growth factor (VEGF), IL-6 and TNF-alpha] from blood, albumin circuit and haemodialysate from four applications. RESULTS: In all four applications, transfer of toxic metabolites (6/6) and inflammatory mediators (6/6), but also of hepatic growth factors (9/10), into the albumin circuit of MARS was consistently detected. Corresponding blood levels were decreased for 3/6 metabolites, 3/6 inflammatory mediators and 1/10 growth factors and increased for 1/10 growth factors. Bridging for liver transplantation was successful with MARS. CONCLUSIONS: In our prospective study, substantial extraction of albumin-bound and water-soluble candidate substances was detected with variable effect on respective blood levels. Notably, essential factors inducing liver regeneration were simultaneously removed. These data provide a basis for evaluation of liver restoration and efficacy of liver support in children with liver failure to devise a collaborative, multicentre trial.

Adolescent↗