Characterization of a receptor for heat shock protein 70 on macrophages and monocytes

Heat shock proteins (Hsps) and molecular chaperones isolated from tumors or virally infected cells elicit an efficient CD8+ T cell response against bound antigenic peptides. This immune response is mediated by presentation of the peptides on MHC class I complexes of antigen-presenting cells (APCs), but the cellular mechanism of this presentation process is not yet understood. Here we provide evidence for the existence of a proteinaceous receptor on the surface of APCs that is specific for mammalian Hsp70. Using a flow cytometry-based assay, saturable binding of Hsp70 to the cell surface of macrophages and peripheral blood monocytes, but not of lymphocytes, can be demonstrated. The affinity of the receptor is in the sub-micromolar range (Kd < 100 nM). Only mammalian Hsc70/Hsp70, but not bacterial Hsp70, is bound with high affinity. Subsequent to binding, Hsp70 is taken up by endocytosis, resulting in an intracellular localization. Our results suggest that receptor-mediated endocytosis forms the basis for the demonstrated efficacy of Hsp70-peptide complexes as anti-tumor vaccines.     

Localization and topology of ratp28, a member of a novel family of putative steroid-binding proteins

We have cloned ratp28, a membrane protein from rat liver homologous to the previously described hpr6.6, a putative steroid-binding protein in humans. Ratp28 has a type II topology as determined by protease digestion experiments on intact and detergent-solubilized membranes. Subcellular fractionation by sucrose density centrifugation revealed a distribution for ratp28 identical to Bip as a marker for membranes of the endoplasmic reticulum. In these experiments no association was found with markers for Golgi or plasma membranes, indicating that ratp28 is localized to the endoplasmic reticulum.     

Oligomerization of peptides analogous to the cytoplasmic domains of coatomer receptors revealed by mass spectrometry

Members of the p24 family of type I transmembrane proteins are involved in budding of coat protein type I (COPI)-coated vesicles. They serve as coat protein receptors, binding via their cytoplasmic domains to coatomer, a stable cytosolic protein complex that represents the major coat component of these vesicles. Experimental evidence suggest that p23, a member of the p24 family, binds to coatomer in an oligomeric state and that this binding triggers polymerization of the coat protein. Toward an understanding of this process at the molecular level, formation of noncovalent complexes and their relative stabilities were analyzed by Fourier transform ion cyclotron resonance mass spectrometry using nanoelectrospray ionization. Specificity and stability of oligomers formed were established to depend on characteristic peptide sequence motifs and were confirmed by mass spectrometric competition experiments with control peptides. Mutations in the peptide sequence caused decreased interaction and destabilization of the noncovalent complexes. The formation and relative stabilities of dimeric and tetrameric complexes were assessed to be formed by cytoplasmic tails of coatomer receptors. The direct molecular identification provided by mass spectrometry correlates well with biochemical results. Thus, electrospray ionization mass spectrometry proves to be a powerful tool to investigate physiologically relevant peptide complexes.     

Enrofloxacin and Macrolides Alone or in Combination with Rifampicin as Antimicrobial Treatment in a Bovine Model of Acute Chlamydia psittaci Infection

Chlamydia psittaci is a zoonotic bacterium with a wide host range that can cause respiratory disease in humans and cattle. In the present study, effects of treatment with macrolides and quinolones applied alone or in combination with rifampicin were tested in a previously established bovine model of respiratory C. psittaci infection. Fifty animals were inoculated intrabronchially at the age of 6–8 weeks. Seven served as untreated controls, the others were assigned to seven treatment groups: (i) rifampicin, (ii) enrofloxacin, (iii) enrofloxacin + rifampicin, (iv) azithromycin, (v) azithromycin + rifampicin, (vi) erythromycin, and (vii) erythromycin + rifampicin. Treatment started 30 hours after inoculation and continued until 14 days after inoculation (dpi), when all animals were necropsied. The infection was successful in all animals and sufficient antibiotic levels were detected in blood plasma and tissue of the treated animals. Reisolation of the pathogen was achieved more often from untreated animals than from other groups. Nevertheless, pathogen detection by PCR was possible to the same extent in all animals and there were no significant differences between treated and untreated animals in terms of local (i.e. cell count and differentiation of BALF-cells) and systemic inflammation (i.e. white blood cells and concentration of acute phase protein LBP), clinical signs, and pathological findings at necropsy. Regardless of the reduced reisolation rate in treated animals, the treatment of experimentally induced respiratory C. psittaci infection with enrofloxacin, azithromycin or erythromycin alone or in combination with rifampicin was without obvious benefit for the host, since no significant differences in clinical and pathological findings or inflammatory parameters were detected and all animals recovered clinically within two weeks.     

HvPIP1;6, a barley (Hordeum vulgare L.) plasma membrane water channel particularly expressed in growing compared with non-growing leaf tissues

The aim of the present study was to identify water channel(s) which are expressed specifically in the growth zone of grass leaves and may facilitate growth-associated water uptake into cells. Previously, a gene had been described (HvEmip) which encodes a membrane intrinsic protein (MIP) and which is particularly expressed in the base 1 cm of barley primary leaves. The functionality of the encoding protein was not known. In the present study on leaf 3 of barley (Hordeum vulgare L.), a clone was isolated, termed HvPIP1;6, which has 99% amino acid sequence identity to HvEmip and belongs to the family of plasma membrane intrinsic proteins (PIPs). Expression of HvPIP1;6 was highest in the elongation zone, where it accounted for >85% of expression of known barley PIP1s. Within the elongation zone, faster grower regions showed higher expression than slower growing regions. Expression of HvPIP1;6 was confined to the epidermis, with some expression in neighboring mesophyll cells. Expression of HvPIP1;6 in Xenopus laevis oocytes increased osmotic water permeability 4- to 6-fold. Water channel activity was inhibited by pre-incubation of oocytes with 50 microM HgCl(2) and increased following incubation with the phosphatase inhibitor okadaic acid or the plant hormone ABA. Plasma membrane preparations were analyzed by Western blots using an antibody that recognized PIP1s. Levels of PIP1s were highest in the elongation and adjacent non-elongation zone. The developmental expression profile of HvPIP2;1, the only known barley water channel belonging to the PIP2 subgroup, was opposite to that of HvPIP1;6.     

The structure of the regulatory domain of the adenylyl cyclase Rv1264 from Mycobacterium tuberculosis with bound oleic acid

The universal secondary messenger cAMP is produced by adenylyl cyclases (ACs). Most bacterial and all eukaryotic ACs belong to class III of six divergent classes. A class III characteristic is formation of the catalytic pocket at a dimer interface and the presence of additional regulatory domains. Mycobacterium tuberculosis possesses 15 class III ACs, including Rv1264, which is activated at acidic pH due to pH-dependent structural transitions of the Rv1264 dimer. It has been shown by X-ray crystallography that the N-terminal regulatory and C-terminal catalytic domains of Rv1264 interact in completely different ways in the active and inhibited states. Here, we report an in-depth structural and functional analysis of the regulatory domain of Rv1264. The 1.6 A resolution crystal structure shows the protein in a tight, disk-shaped dimer, formed around a helical bundle, and involving a protein chain crossover. To understand pH regulation, we determined structures at acidic and basic pH values and employed structure-based mutagenesis in the holoenzyme to elucidate regulation using an AC activity assay. It has been shown that regulatory and catalytic domains must be linked in a single protein chain. The new studies demonstrate that the length of the linker segment is decisive for regulation. Several amino acids on the surface of the regulatory domain, when exchanged, altered the pH-dependence of AC activity. However, these residues are not conserved amongst a number of related ACs. The closely related mycobacterial Rv2212, but not Rv1264, is strongly activated by the addition of fatty acids. The structure resolved the presence of a deeply embedded fatty acid, characterised as oleic acid by mass spectrometry, which may serve as a hinge. From these data, we conclude that the regulatory domain is a structural scaffold used for distinct regulatory purposes.