Vitamin D and autoimmune diabetes

The biologically active form of vitamin D, 1,25(OH)(2)D(3), is a potent modulator of the immune system as well as a regulator of bone and mineral metabolism. Vitamin D-deficiency in infancy and vitamin D receptor gene polymorphisms may be risk factors for insulin-dependent Diabetes mellitus (IDDM). 1,25(OH)(2)D(3) and its analogs significantly repress the development of insulitis and diabetes in the non-obese diabetic (NOD) mouse, a model of human IDDM. 1,25(OH)(2)D(3) may modulate IDDM disease pathogenesis by repression of type I cytokines, inhibition of dendritic cell maturation, and upregulation of regulatory T cells. The function of vitamin D as a genetic and environmental determining factor for IDDM, the protective role of 1,25(OH)(2)D(3) and its analogs in a mouse model of IDDM, and the possible mechanisms by which this protection occurs will be reviewed.     

The unusual extended C-terminal helix of the peroxisomal α/β-hydrolase Lpx1 is involved in dimer contacts but dispensable for dimerization

The yeast peroxisomal hydrolase Lpx1 belongs to the α/β-hydrolase superfamily. In the absence of Lpx1, yeast peroxisomes show an aberrant vacuolated morphology similar to what is found in peroxisomal disorder patients. Here, we present the crystal structure of Lpx1 determined at a resolution of 1.9 ?. The structure reveals the complete catalytic triad with an unusual location of the acid residue after strand β6 of the canonical α/β-hydrolase fold. A four-helix cap domain covers the active site. The interface between the α/β-hydrolase core and the cap domain forms the potential substrate binding site, which may also comprise the tunnel that leads into the protein interior and widens into a cavity. Two further tunnels connect the active site to the protein surface, potentially facilitating substrate access. Lpx1 is a homodimer. The α/β-hydrolase core folds of the two protomers form the dimer contact site. Further dimerization contacts arise from the mutual embracement of the cap domain of one protomer by the non-canonical C-terminal helix of the other, resulting in a total buried surface area of some 6000 ?2. The unusual C-terminal helix sticks out from the core fold to which it is connected by an extended flexible loop. We analyzed whether this helix is required for dimerization and for import of the dimer into peroxisomes using biochemical assays in vitro and a microscopy-based interaction assay in mammalian cells. Surprisingly, the C-terminal helix is dispensable for dimerization and dimer import. The unusually robust self-interaction suggests that Lpx1 is imported into peroxisomes as dimer.     

Establishment of global patterns of planar polarity during growth of the Drosophila wing epithelium

Epithelial tissues develop planar polarity that is reflected in the global alignment of hairs and cilia with respect to the tissue axes. The planar cell polarity (PCP) proteins form asymmetric and polarized domains across epithelial junctions that are aligned locally between cells and orient these external structures. Although feedback mechanisms can polarize PCP proteins intracellularly and locally align polarity between cells, how global PCP patterns are specified is not understood. It has been proposed that the graded distribution of a biasing factor could guide long-range PCP. However, we recently identified epithelial morphogenesis as a mechanism that can reorganize global PCP patterns; in the Drosophila pupal wing, oriented cell divisions and rearrangements reorient PCP from a margin-oriented pattern to one that points distally. Here, we use quantitative image analysis to study how PCP patterns first emerge in the wing. PCP appears during larval growth and is spatially oriented through the activities of three organizer regions that control disc growth and patterning. Flattening morphogen gradients emanating from these regions does not reduce intracellular polarity but distorts growth and alters specific features of the PCP pattern. Thus, PCP may be guided by morphogenesis rather than morphogen gradients.     

Redox and metal ion binding properties of human insulin-like growth factor 1 determined by electrospray ionization mass spectrometry

Insulin-like growth factor 1 (IGF-1) is a 70-residue hormone containing three intramolecular disulfide bridges. IGF-1 and other growth factors are oxidatively folded in the endoplasmic reticulum and act primarily in the blood, under relatively oxidative conditions. It is known that IGF-1 exists in various intracellular and extracellular compartments in the oxidized form; however, the reduction potential of IGF-1 and the ability of fully reduced IGF-1, which contains six cysteine residues, to bind transition metal ions are not known. In this work, we determine that the redox potential of human IGF-1 is equal to -332 mV and the reduced form of hIGF-1 can bind cooperatively four Cu(+) ions, most probably into a tetracopper-hexathiolate cluster. The Cu(+) binding affinity of hIGF-1 is, however, approximately 3 times lower than that for the copper chaperones; thus, we can conclude that fully reduced hIGF-1 cannot compete with known Cu(+)-binding proteins.     

The N-glycans of Trichomonas vaginalis contain variable core and antennal modifications

Trichomonad species are widespread unicellular flagellated parasites of vertebrates which interact with their hosts through carbohydrate-lectin interactions. In the past, some data have been accumulated regarding their lipo(phospho)glycans, a major glycoconjugate on their cell surfaces; on the other hand, other than biosynthetic aspects, few details about their N-linked oligosaccharides are known. In this study, we present both mass spectrometric and high-performance liquid chromatography data about the N-glycans of different strains of Trichomonas vaginalis, a parasite of the human reproductive tract. The major structure in all strains examined is a truncated oligomannose form (Man(5)GlcNAc(2)) with α1,2-mannose residues, compatible with a previous bioinformatic examination of the glycogenomic potential of T. vaginalis. In addition, dependent on the strain, N-glycans modified by pentose residues, phosphate or phosphoethanolamine and terminal N-acetyllactosamine (Galβ1,4GlcNAc) units were found. The modification of N-glycans by N-acetyllactosamine in at least some strains is shared with the lipo(phospho)glycan and may represent a further interaction partner for host galectins, thereby playing a role in binding of the parasite to host epithelia. On the other hand, the variation in glycosylation between strains may be the result of genetic diversity within this species.     

The Mn4Ca photosynthetic water-oxidation catalyst studied by simultaneous X-ray spectroscopy and crystallography using an X-ray free-electron laser

The structure of photosystem II and the catalytic intermediate states of the Mn₄CaO₅ cluster involved in water oxidation have been studied intensively over the past several years. An understanding of the sequential chemistry of light absorption and the mechanism of water oxidation, however, requires a new approach beyond the conventional steady-state crystallography and X-ray spectroscopy at cryogenic temperatures. In this report, we present the preliminary progress using an X-ray free-electron laser to determine simultaneously the light-induced protein dynamics via crystallography and the local chemistry that occurs at the catalytic centre using X-ray spectroscopy under functional conditions at room temperature.     

CEACAM1, a cell-cell adhesion molecule, directly associates with annexin II in a three-dimensional model of mammary morphogenesis

The epithelial cell adhesion molecule CEACAM1 (carcinoembryonic antigen cell adhesion molecule-1) is down-regulated in colon, prostate, breast, and liver cancer. Here we show that CEACAM1-4S, a splice form with four Ig-like ectodomains and a short cytoplasmic domain (14 amino acids), directly associates with annexin II, a lipid raft-associated molecule, which is also down-regulated in many cancers. Annexin II was identified using a glutathione S-transferase pull-down assay in which the cytoplasmic domain of CEACAM-4S was fused to glutathione S-transferase, the fusion protein was incubated with cell lysates, and isolated proteins were sequenced by mass spectrometry. The interaction was confirmed first by reciprocal immunoprecipitations using anti-CEACAM1 and anti-annexin II antibodies and second by confocal laser microscopy showing co-localization of CEACAM1 with annexin II in mammary epithelial cells grown in Matrigel. In addition, CEACAM1 co-localized with p11, a component of the tetrameric AIIt complex at the plasma membrane, and with annexin II in secretory vesicles. Immobilized, oriented peptides from the cytoplasmic domain of CEACAM1-4S were shown to directly associate with bovine AIIt, which is 98% homologous to human AIIt, with average KD values of about 30 nM using surface plasmon resonance, demonstrating direct binding of functionally relevant AIIt to the cytoplasmic domain of CEACAM1-4S.     

In Situ Exposure to Low Herbicide Concentrations Affects Microbial Population Composition and Catabolic Gene Frequency in an Aerobic Shallow Aquifer

The aim of this study was to evaluate how the in situ exposure of a Danish subsurface aquifer to phenoxy acid herbicides at low concentrations (<40 μg l⁻¹) changes the microbial community composition. Sediment and groundwater samples were collected inside and outside the herbicide-exposed area and were analyzed for the presence of general microbial populations, Pseudomonas bacteria, and specific phenoxy acid degraders. Both culture-dependent and culture-independent methods were applied. The abundance of microbial phenoxy acid degraders (10⁰ to 10⁴ g⁻¹ sediment) was determined by most probable number assays, and their presence was only detected in herbicide-exposed sediments. Similarly, PCR analysis showed that the 2,4-dichlorophenoxyacetic acid degradation pathway genes tfdA and tfdB (10² to 10³ gene copies g⁻¹ sediment) were only detected in sediments from contaminated areas of the aquifer. PCR-restriction fragment length polymorphism measurements demonstrated the presence of different populations of tfd genes, suggesting that the in situ herbicide degradation was caused by the activity of a heterogeneous population of phenoxy acid degraders. The number of Pseudomonas bacteria measured by either PCR or plating on selective agar media was higher in sediments subjected to high levels of phenoxy acid. Furthermore, high numbers of CFU compared to direct counting of 4′,6-diamidino-2-phenylindole-stained cells in the microscope suggested an increased culturability of the indigenous microbial communities from acclimated sediments. The findings of this study demonstrate that continuous exposure to low herbicide concentrations can markedly change the bacterial community composition of a subsurface aquifer.     

Amide H/2H exchange reveals a mechanism of thrombin activation

Thrombin is a dual action serine protease in the blood clotting cascade. Similar to other clotting factors, thrombin is mainly present in the blood in a zymogen form, prothrombin. Although the two cleavage events required to activate thrombin are well-known, little is known about why the thrombin precursors are inactive proteases. Although prothrombin is much larger than thrombin, prethrombin-2, which contains all of the same amino acids as thrombin, but has not yet been cleaved between Arg320 and Ile321, remains inactive. Crystal structures of both prethrombin-2 and thrombin are available and show almost no differences in the active site conformations. Slight differences were, however, seen in the loops surrounding the active site, which are larger in thrombin than in most other trypsin-like proteases, and have been shown to be important for substrate specificity. To explore whether the dynamics of the active site loops were different in the various zymogen forms of thrombin, we employed amide H/(2)H exchange experiments to compare the exchange rates of regions of thrombin with the same regions of prothrombin, prethrombin-2, and meizothrombin. Many of the surface loops showed less exchange in the zymogen forms, including the large loop corresponding to anion binding exosite 1. Conversely, the autolysis loop and sodium-binding site exchanged more readily in the zymogen forms. Prothrombin and prethrombin-2 gave nearly identical results while meizothrombin in some regions more closely resembled active thrombin. Thus, cleavage of the Arg320-Ile321 peptide bond is the key to formation of the active enzyme, which involves increased dynamics of the substrate-binding loops and decreased dynamics of the catalytic site.