Controlled cleavage of KLH1 and KLH2 by the V8 protease from Staphylococcus aureus reassociation, electrophoretic and transmission electron microscopy study of peptide fragments.
(65/8246)
The reassociation behaviour of protease V8-cleaved peptides from KLH1 and KLH2, the two hemocyanin isoforms from the giant keyhole limpet Megathura crenulata, has been studied by transmission electron microscopy of negatively stained specimens and SDS/PAGE. Reassociation of the complete mixture of protease cleavage products and of combinations of peptide fragments purified by HPLC was performed in the presence of 100 mm CaCl2 and 100 mm MgCl2 at pH 7.4, over a period of 1 to 4 weeks. The V8 protease splits KLH1 into peptide fragments containing the functional units abc, def, defg, defgh, g and h. This mixture of peptide fragments reassociated to form helical tubular polymers, with a diameter of approximately 25 nm. The single functional units g and h were not incorporated into the polymer. An essentially identical polymer was formed from the re-mixed HPLC-purified fragments abc, def and defg alone. As with uncleaved subunit, the tubular polymer of V8-cleaved KLH1 forms bundles. The combination of peptides def and defg led to the formation of short arc-like filamentous structures, which aggregated but showed little tendency to associate into larger polymers. The KLH1 peptide fragments abc and def alone, did not reassociate and in combination their potential to form polymers was very low. With KLH2, the V8 protease generated peptide fragments containing the functional units abc, defg, defgh and h, which in combination slowly reassociated to form a tubular polymer significantly different to that obtained from the KLH1 V8 fragments. The three-functional unit fragment abc from KLH2 showed no tendency to polymerize and the combination of peptides defg + defgh generated only disordered aggregates, with some indication of malformed tubules. The combination of biochemical and electron microscopical methods enabled the characterization of these polymers with respect to peptide composition and higher order structure. (+info)
Active nucleocytoplasmic shuttling required for function and regulation of stress-activated kinase Spc1/StyI in fission yeast.
(66/8246)
Transcriptional induction of many stress-response genes is dependent on stress-induced nuclear accumulation of stress-activated protein kinases (SAPKs). In the fission yeast Schizosaccharomyces pombe, nuclear accumulation of the SAPK Spc1 (also known as StyI) requires activating phosphorylation catalyzed by the SAPK kinase Wis1; however, it is unknown whether the localization of Spc1 is regulated by nuclear transport factors. Herein are reported studies that show that Spc1 localization is regulated by active transport mechanisms during osmotic stress. Nuclear import of Spc1 requires Pim1, a homologue of the guanine nucleotide exchange factor RCC1 that is essential for nucleocytoplasmic shuttling of proteins. Nuclear export of Spc1 is regulated by the export factor Crm1. An Spc1-Crm1 complex forms as Spc1 is exported from the nucleus. Wis1 and the tyrosine phosphatases Pyp1 and Pyp2 that inactivate Spc1 are excluded from the nucleus by a Crm1-independent mechanism; hence the nuclear import of Spc1 leads to transient isolation from its regulatory proteins. Thus, active nucleocytoplasmic shuttling is required for both the function and regulation of Spc1 during the osmotic shock response. (+info)
Expression of cytotoxic proteins by neoplastic T cells in mycosis fungoides increases with progression from plaque stage to tumor stage disease.
(67/8246)
Granzyme B (GrB) and T-cell-restricted intracellular antigen (TIA-1) are cytotoxic proteins that are specifically expressed by cytotoxic CD4 or CD8 positive T cells and natural killer cells. Recent studies demonstrated frequent expression of GrB and TIA-1 by neoplastic cells in primary cutaneous CD30(+) large T-cell lymphomas and lymphomatoid papulosis but not in CD30(-) large T-cell lymphomas. In the present study, 74 biopsies from 54 patients with mycosis fungoides (MF) were investigated for the expression of GrB and TIA-1 using immunohistochemistry on paraffin sections. Staining of more than 10% of the neoplastic T cells for GrB or TIA-1 was considered positive. All but two follow-up biopsies had been obtained from patients without extracutaneous disease at the time of biopsy. Expression of TIA-1 and GrB was found in 33 (45%) and 14 (19%) of 74 MF biopsies, respectively. Comparison of biopsies from T3NoMo-stage MF (n = 27) and T2NoMo-stage MF (n = 45) showed increased expression of TIA-1 (55 versus 37%) and GrB (33 versus 9%) in T3NoMo-stage MF. Evaluation of multiple sequential biopsies from successive stages of MF also revealed an increase in the GrB/TIA-1 expression with tumor progression in five of eight cases. A clearcut relation between the expression of TIA-1 and/or GrB and the type of skin lesion biopsied was found. Considering all 74 biopsies, expression of TIA-1 and GrB was found in 18 of 50 (35%) and 5 of 50 (10%) patches or plaques, 9 of 16 (55%) and 3 of 16 (20%) tumors without blastic transformation, and 6 of 8 (75%) and 6 of 8 (75%) tumors with blastic transformation (defined as >50% blast cells). Correlation between GrB/TIA-1 expression in first diagnostic biopsies from patches or plaques from 40 patients with T2NoMo-stage MF and clinical follow-up data did not reveal differences in clinical behavior and survival between patients with (n = 14) or without (n = 26) expression of cytotoxic proteins, indicating that MF expressing cytotoxic proteins should not be considered as a separate group. (+info)
A novel function for transforming growth factor-beta1: upregulation of the expression and the IgE-independent extracellular release of a mucosal mast cell granule-specific beta-chymase, mouse mast cell protease-1.
(68/8246)
Intestinal mucosal mast cells (IMMC) express granule neutral proteases that are regulated by T-cell-derived cytokines, including interleukin-3 (IL-3) and IL-9, and by stem cell factor (SCF). The IMMC-specific chymase, mouse mast cell protease-1 (mMCP-1), is released in substantial quantities into the blood stream during gastrointestinal allergic responses. We used cultured bone marrow-derived mast cells (mBMMC) to identify cytokines that regulate the expression and extracellular release of mMCP-1. When grown in IL-3-rich WEHI (15% vol/vol) and 50 ng/mL recombinant rat SCF (rrSCF) bone marrow cells supplemented with IL-9 (5 ng/mL) differentiated into mBMMC that expressed a maximum of less than 250 ng mMCP-1/10(6) cells and 189 ng mMCP-1/mL of culture supernatant. Supplementation of the same three cytokines with transforming growth factor-beta1 (TGF-beta1; 1 ng/mL) resulted in substantially enhanced expression (6 micrograms/10(6) mBMMC) and extracellular release (2 micrograms/mL of culture supernatant) of mMCP-1. The response to TGF-beta1 was dose-dependent, with maximal effect at 1 ng/mL, and was associated with immunohistochemical and ultrastructural changes in the secretory granules. IL-9-induced expression of mMCP-1 may be due to endogenously expressed TGF-beta1, because it was blocked by anti-TGF-beta antibodies. In conclusion, the expression and extracellular release of the IMMC-specific chymase, mMCP-1, is strictly regulated by TGF-beta1. (+info)
New, sensitive fluorogenic substrates for human cathepsin G based on the sequence of serpin-reactive site loops.
(69/8246)
Cathepsin G has both trypsin- and chymotrypsin-like activity, but studies on its enzymatic properties have been limited by a lack of sensitive synthetic substrates. Cathepsin G activity is physiologically controlled by the fast acting serpin inhibitors alpha1-antichymotrypsin and alpha1-proteinase inhibitor, in which the reactive site loops are cleaved during interaction with their target enzymes. We therefore synthesized a series of intramolecularly quenched fluorogenic peptides based on the sequence of various serpin loops. Those peptides were assayed as substrates for cathepsin G and other chymotrypsin-like enzymes including chymotrypsin and chymase. Peptide substrates derived from the alpha1-antichymotrypsin loop were the most sensitive for cathepsin G with kcat/Km values of 5-20 mM-1 s-1. Substitutions were introduced at positions P1 and P2 in alpha1-antichymotrypsin-derived substrates to tentatively improve their sensitivity. Replacement of Leu-Leu in ortho-aminobenzoyl (Abz)-Thr-Leu-Leu-Ser-Ala-Leu-Gln-N-(2, 4-dinitrophenyl)ethylenediamine (EDDnp) by Pro-Phe in Abz-Thr-Pro-Phe-Ser-Ala-Leu-Gln-EDDnp produced the most sensitive substrate of cathepsin G ever reported. It was cleaved with a specificity constant kcat/Km of 150 mM-1 s-1. Analysis by molecular modeling of a peptide substrate bound into the cathepsin G active site revealed that, in addition to the protease S1 subsite, subsites S1' and S2' significantly contribute to the definition of the substrate specificity of cathepsin G. (+info)
Epithelial Na+ channels (ENaC) are inhibited by the cystic fibrosis transmembrane conductance regulator (CFTR) upon activation by protein kinase A. It is, however, still unclear how CFTR regulates the activity of ENaC. In the present study we examined whether CFTR interacts with ENaC by interfering with the Nedd4- and ubiquitin-mediated endocytosis of ENaC. Various C-terminal mutations were introduced into the three alpha-, beta-, and gamma-subunits of the rat epithelial Na+ channel, thereby eliminating PY motifs, which are important binding domains for the ubiquitin ligase Nedd4. When expressed in Xenopus oocytes, most of the ENaC stop (alpha-H647X, beta-P565X, gamma-S608X) or point (alpha-P671A, beta-Y618A, gamma-P(624-626)A) mutations induced enhanced Na+ currents when compared with wild type alpha,beta,gamma-rENaC. However, ENaC currents formed by either of the mutant alpha-, beta-, or gamma-subunits were inhibited during activation of CFTR by forskolin (10 micromol/l) and 3-isobutyl-1-methylxanthine (1 mmol/l). Antibodies to dynamin or ubiquitin enhanced alpha,beta,gamma-rENaC whole cell Na+ conductance but did not interfere with inhibition of ENaC by CFTR. Another mutant, beta-T592M,T593A-ENaC, also showed enhanced Na+ currents, which were down-regulated by CFTR. Moreover, activation of ENaC by extracellular proteases and xCAP1 does not disturb CFTR-dependent inhibition of ENaC. We conclude that regulation of ENaC by CFTR is distal to other regulatory limbs and does not involve Nedd4-dependent ubiquitination. (+info)
Recognition, targeting, and hydrolysis of the lambda O replication protein by the ClpP/ClpX protease.
(71/8246)
It has previously been established that sequences at the C termini of polypeptide substrates are critical for efficient hydrolysis by the ClpP/ClpX ATP-dependent protease. We report for the bacteriophage lambda O replication protein, however, that N-terminal sequences play the most critical role in facilitating proteolysis by ClpP/ClpX. The N-terminal portion of lambda O is degraded at a rate comparable with that of wild type O protein, whereas the C-terminal domain of O is hydrolyzed at least 10-fold more slowly. Consistent with these results, deletion of the first 18 amino acids of lambda O blocks degradation of the N-terminal domain, whereas proteolysis of the O C-terminal domain is only slightly diminished as a result of deletion of the C-terminal 15 amino acids. We demonstrate that ClpX retains its capacity to bind to the N-terminal domain following removal of the first 18 amino acids of O. However, ClpX cannot efficiently promote the ATP-dependent binding of this truncated O polypeptide to ClpP, the catalytic subunit of the ClpP/ClpX protease. Based on our results with lambda O protein, we suggest that two distinct structural elements may be required in substrate polypeptides to enable efficient hydrolysis by the ClpP/ClpX protease: (i) a ClpX-binding site, which may be located remotely from substrate termini, and (ii) a proper N- or C-terminal sequence, whose exposure on the substrate surface may be induced by the binding of ClpX. (+info)
A temperature-dependent switch from chaperone to protease in a widely conserved heat shock protein.
(72/8246)
Misfolding or unfolding of polypeptides can occur as a consequence of environmental stress and spontaneous mutation. The abundance of general chaperones and proteases suggests that cells distinguish between proteins that can be refolded and "hopeless" cases fated to enter the proteolytic pathway. The mechanisms controlling this key metabolic decision are not well understood. We show here that the widely conserved heat shock protein DegP (HtrA) has both general molecular chaperone and proteolytic activities. The chaperone function dominates at low temperatures, while the proteolytic activity is present at elevated temperatures. These results show that a single cellular factor can switch between two key pathways, controlling protein stability and turnover. Implications of this finding for intracellular protein metabolism are discussed. (+info)