Membrane penetration of nonenveloped viruses is a poorly understood process. We have investigated early stages of this process by studying the conformational change experienced by polyomavirus (Py) in the lumen of the endoplasmic reticulum (ER), a step that precedes its transport into the cytosol. We show that a PDI-like protein, ERp29, exposes the C-terminal arm of Py's VP1 protein, leading to formation of a hydrophobic particle that binds to a lipid bilayer; this reaction likely mimics initiation of Py penetration across the ER membrane. Expression of a dominant-negative ERp29 decreases Py infection, indicating ERp29 facilitates viral infection. Interestingly, cholera toxin, another toxic agent that crosses the ER membrane into the cytosol, is unfolded by PDI in the ER. Our data thus identify an ER factor that mediates membrane penetration of a nonenveloped virus and suggest that PDI family members are generally involved in ER remodeling reactions.

Folding and post-translational modification of the thyroid hormone precursor, thyroglobulin (Tg), in the endoplasmic reticulum (ER) of the thyroid epithelial cells is facilitated by several molecular chaperones and folding enzymes, such as BiP, GRP94, calnexin, protein disulfide isomerase, ERp72, and others. They have been shown to associate simultaneously and/or sequentially with Tg in the course of its maturation, thus forming large heterocomplexes in the ER of thyrocytes. Here we present evidence that such complexes include a novel member, an ER-resident lumenal protein, ERp29, which is present in all mammalian tissues with exceptionally high levels of expression in the secretory cells. ERp29 was induced upon treatment of FRTL-5 rat thyrocytes with the thyroid-stimulating hormone, which is essential for the maintenance of thyroid cells and Tg biosynthesis. Chemical cross-linking followed by the cell lysis and immunoprecipitation of ERp29 or Tg revealed association of these proteins and additionally, immunocomplexes that also included major ER chaperones, BiP and GRP94. Sucrose density gradient analysis indicated colocalization of ERp29 with Tg and BiP in the fractions containing large macromolecular complexes. This was supported by immunofluorescent microscopy showing co-localization of ERp29 with Tg in the putative transport vesicular structures. Affinity chromatography using Tg as an affinity ligand demonstrated that ERp29 might be selectively isolated from the FRTL-5 cell lysate or purified lumenal fraction of rat liver microsomes along with the other ER chaperones. Preferential association with the urea-denatured Tg-Sepharose was indicative of either direct or circuitous ERp29/Tg interactions in a chaperone-like manner. Despite the presence of the C-terminal ER-retrieval signal, significant amounts of ERp29 were also recovered from the culture medium of stimulated thyrocytes, indicating ERp29 secretion. Based on these data, we suggest that the function of ERp29 in thyroid cells is connected with folding and/or secretion of Tg.

This review article presents data about the influence of deuterium-depleted water (DDW) on biological systems. It is known that the isotope abundances of natural and bottled waters are variable worldwide. That is why different drinking rations lead to changes of stable isotopes content in body water fluxes in human and animal organisms. Also, intracellular water isotope ratios in living systems depends on metabolic activity and food consumption. We found the 2H/1H gradient in human fluids (δ2H saliva >> δ2H blood plasma > δ2Hbreast milk), which decreases significantly during DDW intake. Moreover, DDW induces several important biological effects in organism (antioxidant, metabolic detoxification, anticancer, rejuvenation, behavior, etc.). Changing the isotope 2H/1H gradient from “2H blood plasma > δ2H visceral organs” to “δ2H blood plasma << δ2H visceral organs” via DDW drinking increases individual adaptation by isotopic shock. The other possible mechanisms of long-term adaptation is DDW influence on the growth rate of cells, enzyme activity and cellular energetics (e.g., stimulation of the mitochondrion activity). In addition, DDW reduces the number of single-stranded DNA breaks and modifies the miRNA profile.

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ERp29, a novel and ubiquitously expressed endoplasmic reticulum (ER) stress-inducible protein, was recently isolated and cDNA cloned in our laboratory. Using size exclusion chromatography and chemical cross-linking we have assessed the oligomerization properties of ERp29. Purified ERp29 in solution as well as in rat hepatoma cells self-associates predominantly into homodimers. Labeling of the cells with [QS S]methionine with subsequent cross-linking and immunoprecipitation showed that ERp29 interacts with a number of ER proteins, one of which was previously identified as BiP/GRP78. Secondary structure prediction and fold recognition methods indicate that the native conformation of ERp29 resembles the thioredoxin fold, a structural motif characteristic of a number of enzymes with the redox function, including protein disulfide isomerase (with which ERp29 shares limited sequence similarity). Dimerization of the protein is suggested to be advantageous for the protein binding potential of ERp29.z 1998 Federation of European Biochemical Societies.