The disulfide-bonded loop of chromogranin B mediates membrane binding and directs sorting from the trans-Golgi network to secretory granules.
The disulfide-bonded loop of chromogranin B (CgB), a regulated secretory protein with widespread distribution in neuroendocrine cells, is known to be essential for the sorting of CgB from the trans-Golgi network (TGN) to immature secretory granules. Here we show that this loop, when fused to the constitutively secreted protein alpha1-antitrypsin (AT), is sufficient to direct the fusion protein to secretory granules. Importantly, the sorting efficiency of the AT reporter protein bearing two loops (E2/3-AT-E2/3) is much higher compared with that of AT with a single disulfide-bonded loop. In contrast to endogenous CgB, E2/3-AT-E2/3 does not undergo Ca2+/pH-dependent aggregation in the TGN. Furthermore, the disulfide-bonded loop of CgB mediates membrane binding in the TGN and does so with 5-fold higher efficiency if two loops are present on the reporter protein. The latter finding supports the concept that under physiological conditions, aggregates of CgB are the sorted units of cargo which have multiple loops on their surface leading to high membrane binding and sorting efficiency of CgB in the TGN. (+info)
Chaperone activity with a redox switch.
Hsp33, a member of a newly discovered heat shock protein family, was found to be a very potent molecular chaperone. Hsp33 is distinguished from all other known molecular chaperones by its mode of functional regulation. Its activity is redox regulated. Hsp33 is a cytoplasmically localized protein with highly reactive cysteines that respond quickly to changes in the redox environment. Oxidizing conditions like H2O2 cause disulfide bonds to form in Hsp33, a process that leads to the activation of its chaperone function. In vitro and in vivo experiments suggest that Hsp33 protects cells from oxidants, leading us to conclude that we have found a protein family that plays an important role in the bacterial defense system toward oxidative stress. (+info)
Insulin-like growth factors I and II are unable to form and maintain their native disulfides under in vivo redox conditions.
Insulin-like growth factor (IGF) I does not quantitatively form its three native disulfide bonds in the presence of 10 mM reduced and 1 mM oxidized glutathione in vitro [Hober, S. et al. (1992) Biochemistry 31, 1749-1756]. In this paper, we show (i) that both IGF-I and IGF-II are unable to form and maintain their native disulfide bonds at redox conditions that are similar to the situation in the secretory vesicles in vivo and (ii) that the presence of protein disulfide isomerase does not overcome this problem. The results indicate that the previously described thermodynamic disulfide exchange folding problem of IGF-I in vitro is also present in vivo. Speculatively, we suggest that the thermodynamic disulfide exchange properties of IGF-I and II are biologically significant for inactivation of the unbound growth factors by disulfide exchange reactions to generate variants destined for rapid clearance. (+info)
In vivo formation of Cu,Zn superoxide dismutase disulfide bond in Escherichia coli.
We have found that the in vivo folding of periplasmic Escherichia coli Cu,Zn superoxide dismutase is assisted by DsbA, which catalyzes the efficient formation of its single disulfide bond, whose integrity is essential to ensure full catalytic activity to the enzyme. In line with these findings, we also report that the production of recombinant Xenopus laevis Cu,Zn superoxide dismutase is enhanced when the enzyme is exported in the periplasmic space or is expressed in thioredoxin reductase mutant strains. Our data show that inefficient disulfide bond oxidation in the bacterial cytoplasm inhibits Cu,Zn superoxide dismutase folding in this cellular compartment. (+info)
Scrotal heat stress induces altered sperm chromatin structure associated with a decrease in protamine disulfide bonding in the stallion.
A variety of testicular insults can induce changes in the structure of spermatozoal chromatin, resulting in spermatozoal DNA that is more susceptible to acid-induced denaturation. The degree of change in the DNA can be measured using the sperm chromatin structure assay (SCSA). The SCSA measures the relative amounts of single- and double-stranded DNA after staining with the metachromatic dye, acridine orange. Here we used a stallion model (n = 4) to study the effects of scrotal heat stress on spermatozoal DNA. This model was created by insulating stallion testes for 48 h and collecting sperm daily thereafter for 60 days. Changes in the SCSA were then correlated with protamine disulfide content and protamine types and levels. Results of the SCSA indicated that the susceptibility of spermatozoal DNA to denaturation was dependent on the spermatogenic cell stage that the ejaculated sperm was in at the time of the heat stress. Spermatozoa with altered DNA had a decrease in the extent of disulfide bonding that was associated with an increase in the susceptibility of DNA to denaturation. However, there were no detectable changes in either the protamine type or level. Thus, in this model, decreased disulfide bonding is associated with an increased susceptibility of spermatozoal DNA to denaturation in the absence of protamine changes. (+info)
An intact sperm nuclear matrix may be necessary for the mouse paternal genome to participate in embryonic development.
We have been interested in determining the minimally required elements in the sperm head that are necessary in order for the paternal genome to participate in embryogenesis. We used an ionic detergent, mixed alkyltrimethylammonium bromide (ATAB), plus dithiothreitol (DTT) to remove the acrosome and almost all of the perinuclear theca, leaving only the sperm nucleus morphologically intact. We also tested the stability of the sperm nuclear matrix by the ability to form nuclear halos. Sperm nuclei washed in freshly prepared 0.5% ATAB + 2 mM DTT completely decondensed when extracted with salt, but nuclei washed in the same buffer that was 1 wk old, and then extracted with salt, produced nuclear halos, indicating stable nuclear matrices. When we treated sperm heads with freshly prepared ATAB+DTT and injected them into oocytes, none of the oocytes developed into live offspring. In contrast, sperm heads treated in the same way but with 1-wk-old ATAB+DTT solution could support development of about 30% of the oocytes to live offspring. Electron microscopy demonstrated that most of the perinuclear theca had been removed in both cases. These data suggest that at least in the mouse, the only component of the spermatozoa that is crucial for participation in embryologic development is the sperm nucleus with a stable nuclear matrix. (+info)
The internal Cys-207 of sorghum leaf NADP-malate dehydrogenase can form mixed disulphides with thioredoxin.
The role of the internal Cys-207 of sorghum NADP-malate dehydrogenase (NADP-MDH) in the activation of the enzyme has been investigated through the examination of the ability of this residue to form mixed disulphides with thioredoxin mutated at either of its two active-site cysteines. The h-type Chlamydomonas thioredoxin was used, because it has no additional cysteines in the primary sequence besides the active-site cysteines. Both thioredoxin mutants proved equally efficient in forming mixed disulphides with an NADP-MDH devoid of its N-terminal bridge either by truncation, or by mutation of its N-terminal cysteines. They were poorly efficient with the more compact WT oxidised NADP-MDH. Upon mutation of Cys-207, no mixed disulphide could be formed, showing that this cysteine is the only one, among the four internal cysteines, which can form mixed disulphides with thioredoxin. These experiments confirm that the opening of the N-terminal disulphide loosens the interaction between subunits, making Cys-207, located at the dimer contact area, more accessible. (+info)
Hairpin-shaped DNA duplexes with disulfide bonds in sugar-phosphate backbone as potential DNA reagents for crosslinking with proteins.
Convenient approaches were described to incorporate -OP(=O)O(-)-SS-O(-)(O=)PO- bridges in hairpin-shaped DNA duplexes instead of regular phosphodiester linkages: (i) H2O2- or 2,2'-dipyridyldisulfide-mediated coupling of 3'- and 5'-thiophosphorylated oligonucleotides on complementary template and (ii) more selective template-guided autoligation of a preactivated oligonucleotide derivative with an oligomer carrying a terminal thiophosphoryl group. Dithiothreitol was found to cleave completely modified internucleotide linkage releasing starting oligonucleotides. The presence of complementary template as an intrinsic element of the molecule protects the hairpin DNA analog from spontaneous exchange of disulfide-linked oligomer fragments and makes it a good candidate for auto-crosslinking with cysteine-containing proteins. (+info)