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Pseudomonas aeruginosa produces the siderophores pyoverdin and pyochelin as well as receptors for siderophores in response to iron deprivation. Previously, it has been shown in vitro that at neutral pH purified pyoverdin acquires iron from transferrin only in the presence of P. aeruginosa elastase (LasB), which proteolytically degrades transferrin. We constructed a LasB-negative mutant, PAO1E, by insertional mutagenesis to investigate whether this mutant differs in growth from the parental strain PA01 in an iron-depleted medium supplemented with transferrin or human serum. PAO1 and PAOIE did not differ in growth with 1.25 ,uM Fe2-transferrin as the only iron source. Urea gel electrophoresis indicated iron release from intact transferrin during the logarithmic growth phase of PAO1 and PAO1E. A total of 333 ,uM LasB was synthesized from PAOI after onset of stationary-phase growth. Quantification of pyoverdin by spectroscopy revealed that up to 900 ,uM pyoverdin was produced during growth of the strains in medium supplemented with Fe2-transferrin or 10%o human serum. Incubation of Fe2-transferrin and purified pyoverdin in concentrations similar to those found in the culture supernatant resulted in release of iron from transferrin after 10 h at 37°C. However, LasB significantly enhanced the rate constant for iron acquisition of pyoverdin from transferrin. We conclude that P. aeruginosa can use transferrin as an iron source without further need of LasB or pH changes. This is further supported by experiments with P. aeruginosa K437, which has a defective iron uptake system, and its LasB-negative mutant, K437E. Though K437 and K437E did not differ in growth with Fe2-transferrin as the only iron source, their growth was significantly reduced relative to that of PAO1 and PAO1E. In spite of the virtual absence of freely available iron in the human body, pathogenic bacteria can successfully multiply in vivo to establish infection. The iron transport proteins transferrin and lactoferrin are thought to serve as the iron source for bacteria in the human body fluids (16). Pseudomonas aeruginosa, like other pathogens, produces siderophores during iron deprivation which bind Fe3" and deliver the iron to

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We have expressed recombinant human vitamin D receptor and its ligand-binding domain in Spodoptera frugiperda (Sf9) insect cells with a 30-litre bioreactor. Both proteins were purified to apparent homogeneity with yields of 0.5-3.5 mg\l. Gel-filtration analyses indicated that the purified human vitamin D receptor and its ligand-binding domain were present as monomers in solution. The purified vitamin D receptor and its ligand-binding domain were demonstrated to bind 1α,25-dihydroxyvitamin D $ with high affinity, the K d values ranging from 0.9 to 1.2 nM. Neutron scattering studies of the ligand-binding domain demonstrated that the samples are homogeneous and contain monomeric species of polypeptides. The purified vitamin D receptor

The activities of 1α,25-dihydroxyvitamin D3, 1,25D3, are mediated via its binding to the vitamin D receptor (VDR), a ligand-dependent transcription factor that belongs to the nuclear receptor superfamily. Numerous studies have demonstrated the important role of 1,25D3 and VDR signaling in various biological processes and associated pathologies. A wealth of information about ligand recognition and mechanism of action by structural analysis of the VDR complexes is also available. The methods used in these structural studies were mainly X-ray crystallography complemented by NMR, cryo-electron microscopy and structural mass spectrometry. This review aims to provide an overview of the current knowledge of VDR structures and also to explore the recent progress in understanding the complex mechanism of action of 1,25D3 from a structural perspective.

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A negatively-regulated aggregation mechanism is likely to be common for pore-forming peptides. The positively-charged domain B of perforin (residues 7- 15) may mediate cooperativity through electrostatic interactions. Such a mechanism limits the number of protein molecules that are committed to any particular channel. This data supports smaller pores as the physiologically relevant aggregate, rather than the larger ring sizes identified by electron microscopy at higher, non-biological concentrations.

Retinoic-acid-related Orphan Receptors (RORs) regulate maintenance of the circadian rhythm and immune response among others and are involved in increasing number of pathologies including autoimmune diseases, cancer and neurological disorders...