Hsp70 family member, mot-2/mthsp70/GRP75, binds to the cytoplasmic sequestration domain of the p53 protein

Hsp70 family member mot-2/mthsp70/GRP75/PBP74 was shown to bind to the tumor suppressor protein p53. In this study, by in vivo coimmunoprecipitation of mot-2 with p53 and its deletion mutants, the mot-2 binding site of p53 was mapped to its C-terminal amino acid residues 312-352, a region of p53 that includes its cytoplasmic sequestration domain. These data demonstrate that cytoplasmic sequestration and inactivation of p53 by mot-2 occurs by its binding to the cytoplasmic sequestration domain. Therefore, perturbation of mot-p53 interactions can be employed to abrogate cytoplasmic retention of wild-type p53 in tumors.     

Persistent and transient replication of full-length hepatitis C virus genomes in cell culture

The recently developed subgenomic hepatitis C virus (HCV) replicons were limited by the fact that the sequence encoding the structural proteins was missing. Therefore, important information about a possible influence of these proteins on replication and pathogenesis and about the mechanism of virus formation could not be obtained. Taking advantage of three cell culture-adaptive mutations that enhance RNA replication synergistically, we generated selectable full-length HCV genomes that amplify to high levels in the human hepatoma cell line Huh-7 and can be stably propagated for more than 6 months. The structural proteins are efficiently expressed, with the viral glycoproteins E1 and E2 forming heterodimers which are stable under nondenaturing conditions. No disulfide-linked glycoprotein aggregates were observed, suggesting that the envelope proteins fold productively. Electron microscopy studies indicate that cell lines harboring these full-length HCV RNAs contain lipid droplets. The majority of the core protein was found on the surfaces of these structures, whereas the glycoproteins appear to localize to the endoplasmic reticulum and cis-Golgi compartments. In agreement with this distribution, no endoglycosidase H-resistant forms of these proteins were detectable. In a search for the production of viral particles, we noticed that these cells release substantial amounts of nuclease-resistant HCV RNA-containing structures with a buoyant density of 1.04 to 1.1 g/ml in iodixanol gradients. The same observation was made in transient-replication assays using an authentic highly adapted full-length HCV genome that lacks heterologous sequences. However, the fact that comparable amounts of such RNA-containing structures were found in the supernatant of cells carrying subgenomic replicons demonstrates a nonspecific release independent of the presence of the structural proteins. These results suggest that Huh-7 cells lack host cell factors that are important for virus particle assembly and/or release.     

An Hsp70 family chaperone,mortalin/mthsp70/PBP74/Grp75: what,when, and where?

Mortalin/mthsp70/PBP74/Grp75 (called mortalin hereafter), a member of the Hsp70 family of chaperones, was shown to have different subcellular localizations in normal and immortal cells. It has been assigned to multiple subcellular sites and implicated in multiple functions ranging from stress response, intracellular trafficking, antigen processing, control of cell proliferation, differentiation, and tumorigenesis. The present article compiles and reviews information on the multiple sites and functions of mortalin in different organisms. The relevance of its differential distributions and functions in normal and immortal cell phenotypes is discussed.     

Thermodynamics of aminoglycoside-rRNA recognition: the binding of neomycin-class aminoglycosides to the A site of 16S rRNA

We use spectroscopic and calorimetric techniques to characterize the binding of the aminoglycoside antibiotics neomycin, paromomycin, and ribostamycin to a RNA oligonucleotide that models the A-site of Escherichia coli 16S rRNA. Our results reveal the following significant features: (i) Aminoglycoside binding enhances the thermal stability of the A-site RNA duplex, with the extent of this thermal enhancement decreasing with increasing pH and/or Na(+) concentration. (ii) The RNA binding enthalpies of the aminoglycosides become more exothermic (favorable) with increasing pH, an observation consistent with binding-linked protonation of one or more drug amino groups. (iii) Isothermal titration calorimetry (ITC) studies conducted as a function of buffer reveal that aminoglycoside binding to the host RNA is linked to the uptake of protons, with the number of linked protons being dependent on pH. Specifically, increasing the pH results in a corresponding increase in the number of linked protons. (iv) ITC studies conducted at 25 and 37 degrees C reveal that aminoglycoside-RNA complexation is associated with a negative heat capacity change (Delta C(p)), the magnitude of which becomes greater with increasing pH. (v) The observed RNA binding affinities of the aminoglycosides decrease with increasing pH and/or Na(+) concentration. In addition, the thermodynamic forces underlying these RNA binding affinities also change as a function of pH. Specifically, with increasing pH, the enthalpic contribution to the observed RNA binding affinity increases, while the corresponding entropic contribution to binding decreases. (vi) The affinities of the aminoglycosides for the host RNA follow the hierarchy neomycin > paromomycin > ribostamycin. The enhanced affinity of neomycin relative to either paromomycin or ribostamycin is primarily, if not entirely, enthalpic in origin. (vii) The salt dependencies of the RNA binding affinities of neomycin and paromomycin are consistent with at least three drug NH(3)(+) groups participating in electrostatic interactions with the host RNA. In the aggregate, our results reveal the impact of specific alterations in aminoglycoside structure on the thermodynamics of binding to an A-site model RNA oligonucleotide. Such systematic comparative studies are critical first steps toward establishing the thermodynamic database required for enhancing our understanding of the molecular forces that dictate and control aminoglycoside recognition of RNA.     

A high-throughput amenable colorimetric assay for enantioselective screening of nitrilase-producing microorganisms using pH sensitive indicators

Based on the color change of an indicator due to the release of hydrogen ion from a nitrilase-catalyzed reaction, a rapid colorimetric method was established for the enantioselective screening of nitrilase-producing microorganisms. The formation of acids due to the nitrilase-mediated hydrolysis of nitriles causes a drop in the pH, which in turn results in a change of color of the solution (containing indicator) that can be observed visually. The buffer (0.01 M phosphate, pH 7.2) and indicator (Bromothymol blue, 0.01%) were selected in such a way that both have the same affinity for the released protons. The enantioselectivity of nitrilases was estimated by comparing the hydrolysis of (R)-mandelonitrile with that of racemate under the same conditions. The method was used to screen a library of nitrilase-producing microorganisms, isolated in the authors' laboratory for their ability to enantioselectively hydrolyze mandelonitrile to mandelic acid, an important chiral building block.     

Distribution of cells bearing B-cell alloantigen(s) in North Indian rheumatic fever/rheumatic heart disease patients

Numerous investigators have developed monoclonal antibodies against B-cell alloantigen(s) of rheumatic fever. However, the developed monoclonals do not have the same significance in all the populations. We have developed a battery of monoclonals against B-cell alloantigens of North Indian rheumatic fever patients. In the present study, we have used these monoclonals to examine the frequency of rheumatic antigens in 30 patients with recurrence of rheumatic activity (RRA), 30 of rheumatic heart disease (RHD) patients and 50 controls using alkaline phosphatase anti-alkaline phosphatase (APAAP) technique. These patients were examined at the time of registry and after three months follow up. RRA patients showed higher percentage of lymphocyte positive as compare to RHD and controls. Interestingly, On follow-up RRA patients showed significant decline in positive lymphocyte as compare to first visit whereas no such change was observed in RHD patients. There were 90–93% of RRA and RHD patients positive with these monoclonals. A significant age variation of rheumatic cells was also noticed in all groups of rheumatic patients. We conclude that monoclonals raised from the same ethnic population are highly specific and cost effective to use them to develop an easy field test system such as APAAP, to identify the individual at risk, to develop rheumatic fever. It is also suggested that the alloantigen marker may persist through out life and gets activated after recurrence of the disease.     

Analysis of a donor gene region for a variant surface glycoprotein and its expression site in African trypanosomes

African trypanosomes evade the immune response of their mammalian hosts by sequentially expressing genes for different variant surface glycoproteins (VSGs) from telomere-linked VSG expression sites. In the Trypanosoma brucei clone whose genome is being sequenced (GUTat 10.1), we show that the expressed VSG (VSG 10.1) is duplicated from a silent donor VSG located at another telomere-linked site. We have determined two 130 kb sequences representing the VSG 10.1 donor and expression sites. The telomere-linked donor VSG 10.1 resembles metacyclic VSG expression sites, and is preceded by a cluster of 35 or more tandem housekeeping genes, all of which are transcribed away from the telomere. The 45 kb telomere-linked VSG 10.1 expression site contains a promoter followed by seven expression site-associated genes (ESAGs), three pseudo ESAGs, two pseudo VSGs and VSG 10.1. The 80 kb preceding the expression site has few, if any, functional ORFs, but contains 50 bp repeats, INGI retrotransposon-like elements, and novel 4–12 kb repeats found near other telomeres. This analysis provides the first look over a 130 kb range of a telomere-linked donor VSG and its corresponding telomere-linked VSG expression site and forms the basis for studies on antigenic variation in the context of a completely sequenced genome.