[Anaerobic infection and its rapid detection in surgical patients]

OBJECTIVE

To investigate anaerobic infection and its rapid detection in surgical patients.

METHODS

372 specimens were collected from surgical patients for anaerobe detection. To find a rapid detectable method, 110 specimens were collected for comparative studies by using indirect immunofluorescent antibody technique (IFA), enzyme labeled antibody technique (ELAT) and general cultural method (CM).

RESULTS

The isolation rate of anaerobes was rather high in pyothorax (88.9%), abdominal abscess (86.7%), appendicitis (83.9%) and cerebral abscess (all five cases were positive). In burn wounds, the rate was about 23.6% especially in deep burn wounds. Among 212 strains detected, the predominant anaerobes were as follows B. melaninogenicus (28.8%), B. fragilis (25%), F. nucleatum (7.5%), C. perfringens (7.5%), and peptostreptococcus (5.7%); most of them (87.8%) were non-sporing anaerobes. Mixed infection with aerobes accounted for 64%. The survey of rapid detection was conducted in B. fragilis, B. melaninogenicus, C. perfringens, F. nucleatum and peptostreptococcus. The detectable rate was higher in IFA (79.1%) and ELAT (80.9%) than in CM (37.3%).

CONCLUSION

IFA and ELAT might be rapid, specific, sensitive, and simple for detecting anaerobes.

Roles of tyrosine 158 and lysine 165 in the catalytic mechanism of InhA, the enoyl-ACP reductase from Mycobacterium tuberculosis

The role of tyrosine 158 (Y158) and lysine 165 (K165) in the catalytic mechanism of InhA, the enoyl-ACP reductase from Mycobacterium tuberculosis, has been investigated. These residues have been identified as putative catalytic residues on the basis of structural and sequence homology with the short chain alcohol dehydrogenase family of enzymes. Replacement of Y158 with phenylalanine (Y158F) and with alanine (Y158A) results in 24- and 1500-fold decreases in k(cat), respectively, while leaving K(m) for the substrate, trans-2-dodecenoyl-CoA, unaffected. Remarkably, however, replacement of Y158 with serine (Y158S) results in an enzyme with wild-type activity. Kinetic isotope effect studies indicate that the transfer of a solvent-exchangeable proton is partially rate-limiting for the wild-type and Y158S enzymes, but not for the Y158A enzyme. These data indicate that Y158 does not function formally as a proton donor in the reaction but likely functions as an electrophilic catalyst, stabilizing the transition state for hydride transfer by hydrogen bonding to the substrate carbonyl. A conformational change involving rotation of the Y158 side chain upon binding of the enoyl substrate to the enzyme is proposed as an explanation for the inverse solvent isotope effect observed on V/K(DD-CoA) when either NADH or NADD is used as the reductant. These data are consistent with the recently published structure of a C16 fatty acid substrate bound to InhA that shows Y158 hydrogen bonded to the substrate carbonyl group and rotated from the position it occupies in the InhA-NADH binary complex [Rozwarski, D. A., Vilcheze, C., Sugantino, M., Bittman, R., and Sacchettini, J. C. (1999) J. Biol. Chem. 274, 15582-15589]. Finally, the role of K165 has been analyzed using site-directed mutagenesis. Replacement of K165 with glutamine (K165Q) and arginine (K165R) has no effect on the enzyme's catalytic ability or on its ability to bind NADH. However, the K165A and K165M enzymes are unable to bind NADH, indicating that K165 has a primary role in cofactor binding.

KDEL proteins are found on the surface of NG108-15 cells

Although KDEL proteins are primarily localized to the endoplasmic reticulum (ER), we have employed surface biotinylation method to demonstrate that the KDEL proteins calreticulin (Crt), protein disulfide isomerase (PDI) and the 78-kDa glucose regulated protein (GRP78) are found on the surface of the NG108-15 cell line. In contrast, the 94-kDa glucose regulated protein (GRP94), another KDEL protein, is not found on the cell surface. Calnexin (Cnx), a type-1 integral transmembrane ER protein which is partially homologous to Crt but lacks the KDEL sequence, is not detected on the cell surface either. While only small amounts of the total GRP78, PDI and Crt molecules exist on the cell surface at steady state, a significant fraction of the newly synthesized molecules are transported to the cell surface and transport of these proteins is inhibited by treatment with brefeldin A. The surface GRP78 contains the KDEL sequence. On the cell surface, GRP78, PDI and Crt associate with other proteins and form complexes of different sizes. Surface Crt is found to be essential for the neurite formation when NG108-15 cells are induced to differentiate using dibutyryl cAMP.

Heteronuclear NMR and crystallographic studies of wild-type and H187Q Escherichia coli uracil DNA glycosylase: electrophilic catalysis of uracil expulsion by a neutral histidine 187

The nature of the putative general acid His187 in the reaction catalyzed by Escherichia coli uracil DNA glycosylase (UDG) was investigated using X-ray crystallography and NMR spectroscopy. The crystal structures of H187Q UDG, and its complex with uracil, have been solved at 1.40 and 1.60 A resolution, respectively. The structures are essentially identical to those of the wild-type enzyme, except that the side chain of Gln187 is turned away from the uracil base and cannot interact with uracil O2. This result provides a structural basis for the similar kinetic properties of the H187Q and H187A enzymes. The ionization state of His187 was directly addressed with (1)H-(15)N NMR experiments optimized for histidine ring spin systems, which established that His187 is neutral in the catalytically active state of the enzyme (pK(a) <5.5). These NMR experiments also show that His187 is held in the N(epsilon)()2-H tautomeric form, consistent with the crystallographic observation of a 2.9 A hydrogen bond from the backbone nitrogen of Ser189 to the ring N(delta)()1 of His187. The energetic cost of breaking this hydrogen bond may contribute significantly to the low pK(a) of His187. Thus, the traditional view that a cationic His187 donates a proton to uracil O2 is incorrect. Rather, we propose a concerted mechanism involving general base catalysis by Asp64 and electrophilic stabilization of the developing enolate on uracil O2 by a neutral His187.

[Development of continuous rat infusion device]

In order to perform better scientific researches on fluid resuscitation, total parenteral nutrition and continuous drug administration in rats, we developed a set of rat infusion device. The device, the characteristics of reasonable design, simple operation, low cost, good practicability, and making it by oneself or buying a whole set, can not only assure rats to run around, drink water, eat food freely, but also insure continuous infusion and drug administration during the experimental study of rats.

Effect of benzene, toluene, xylene on the semen quality of exposed workers

OBJECTIVE

To examine the effects on semen and sperm quality of workers after a short and long term exposure to benzene, toluene, and xylene.

METHODS

The semen and blood of 24 married workers exposed to benzene, toluene, and xylene from shoemaking, spray painting, or paint manufacturing factories were collected. The concentration of benzene, toluene, and xylene in the blood and semen was determined by using headspace chromatographic method. Routine sperm test was carried out and acrosin activity detected.

RESULTS

The results showed that benzene, toluene, and xylene were found in the blood and semen of some ex-workers in a working environment where the air concentration of benzene, toluene, and xylene exceeded the maximum allowable concentration (MAC). This result was not found in workers of the control group. There were also some effects on the quality of semen in the exposed workers. For example, the percentage of semen with liquefaction time exceeding 30 minutes increased. The sperm vitality, motility and acrosin activity decreased. At the same time, there were a positive correlation between liquefaction time and the level of toluene in semen, and a negative correlation between sperm vitality, sperm activity or acrosin activity and working history.

CONCLUSIONS

The results suggested that the mixture could affect the quality of semen and sperm, which might be the main reason of the abnormal pregnancy outcome among the wives of workers exposed to benzene, toluene, and xylene. Further studies are, however, required to confirm these findings.

Structural basis and mechanism of enoyl reductase inhibition by triclosan

The enoyl-acyl carrier protein reductase (ENR) is involved in bacterial fatty acid biosynthesis and is the target of the antibacterial diazaborine compounds and the front-line antituberculosis drug isoniazid. Recent studies suggest that ENR is also the target for the broad-spectrum biocide triclosan. The 1.75 A crystal structure of EnvM, the ENR from Escherichia coli, in complex with triclosan and NADH reveals that triclosan binds specifically to EnvM. These data provide a molecular mechanism for the antibacterial activity of triclosan and substantiate the hypothesis that its activity results from inhibition of a specific cellular target rather than non-specific disruption of the bacterial cell membrane. This has important implications for the emergence of drug-resistant bacteria, since triclosan is an additive in many personal care products such as toothpastes, mouthwashes and soaps. Based on this structure, rational design of triclosan derivatives is possible which might be effective against recently identified triclosan-resistant bacterial strains.

Isolation and characterization of MC3T3-E1 preosteoblast subclones with distinct in vitro and in vivo differentiation/mineralization potential

A series of subclonal cell lines with high or low differentiation/mineralization potential after growth in the presence of ascorbic acid (AA) were derived from murine MC3T3-E1 cells. Subclones were characterized in terms of their ability to mineralize a collagenous extracellular matrix both in vitro and in vivo and express osteoblast-related genes. When compared with nonmineralizing cells, mineralizing subclones selectively expressed mRNAs for the osteoblast markers, bone sialoprotein (BSP), osteocalcin (OCN), and the parathyroid hormone (PTH)/parathyroid hormone-related protein (PTHrP) receptor. In contrast, alkaline phosphatase mRNA was present in certain nonmineralizing as well as mineralizing subclones, suggesting that its expression may be subject to different controls from other osteoblast markers. Only highly differentiating subclones exhibited strong AA-dependent induction of a transiently transfected OCN promoter-luciferase reporter gene, indicating that there was a good correlation between mRNA levels and transcriptional activity. Consistent with its postulated role in biomineralization, BSP as measured by Western blotting was only present in mineralizing subclones. After implantation into immunodeficient mice, highly differentiating subclones formed bone-like ossicles resembling woven bone, while poorly differentiating cells only produced fibrous tissue. Interestingly, subclones with both high and low differentiation potential produced similar amounts of collagen in culture and expressed comparable basal levels of mRNA encoding Osf2/Cbfa1, an osteoblast-related transcription factor. Although some strongly differentiating cells exhibited a modest AA-dependent up-regulation of Osf2/Cbfa1 mRNA, there was no clear relationship between levels of this message and induction of mRNAs for other differentiation markers. Thus, the mere presence of Osf2/Cbfa1 in a subclone was not sufficient for osteoblast differentiation. These subclones will be very useful for studying critical events in osteoblast differentiation and mineralization.

[Digital subtraction angiography of cerebrum for diagnosis of cavernous sinus fistula and its intravascular treatment]

OBJECTIVE

To evaluate the diagnosis of digital subtraction angiography (DSA) of cerebral arteries and the intravascular treatment for carotid artery-cavernous sinus fistula (CCF) mainly manifesting as pulsating exophthalmos.

METHODS

Digital subtraction angiography (DSA) of cerebral arteries was carried out for 15 patients with pulsating exophthalmos. Of them, detectable balloon and tungsten filament microcoil were used for intravascular embolism treatment in 12 cases, and the 3 cases with CCF of the branch of external carotid artery were not treated.

RESULTS

Of the 15 cases, 12 were fallen in the CCF of high flow type of unilateral internal carotid artery, and 3 in the CCF of low flow type of unilateral external carotid artery. The symptoms and signs of intravascular embolism disappeared after treatment in 11 cases.

CONCLUSION

Cerebral artery DSA and intravascular therapy are the ideal methods for the diagnosis and treatment of CCF mainly manifesting as pulsating exophthalmos.

Crystal structure of Escherichia coli uracil DNA glycosylase and its complexes with uracil and glycerol: structure and glycosylase mechanism revisited

The DNA repair enzyme uracil DNA glycosylase (UDG) catalyzes the hydrolysis of premutagenic uracil residues from single-stranded or duplex DNA, producing free uracil and abasic DNA. Here we report the high-resolution crystal structures of free UDG from Escherichia coli strain B (1.60 A), its complex with uracil (1.50 A), and a second active-site complex with glycerol (1.43 A). These represent the first high-resolution structures of a prokaryotic UDG to be reported. The overall structure of the E. coli enzyme is more similar to the human UDG than the herpes virus enzyme. Significant differences between the bacterial and viral structures are seen in the side-chain positions of the putative general-acid (His187) and base (Asp64), similar to differences previously observed between the viral and human enzymes. In general, the active-site loop that contains His187 appears preorganized in comparison with the viral and human enzymes, requiring smaller substrate-induced conformational changes to bring active-site groups into catalytic position. These structural differences may be related to the large differences in the mechanism of uracil recognition used by the E. coli and viral enzymes. The pH dependence of k(cat) for wild-type UDG and the D64N and H187Q mutant enzymes is consistent with general-base catalysis by Asp64, but provides no evidence for a general-acid catalyst. The catalytic mechanism of UDG is critically discussed with respect to these results.

Suppression of breast cancer growth and metastasis by a serpin myoepithelium-derived serine proteinase inhibitor expressed in the mammary myoepithelial cells

A serpin was identified in normal mammary gland by differential cDNA sequencing. In situ hybridization has detected this serpin exclusively in the myoepithelial cells on the normal and noninvasive mammary epithelial side of the basement membrane and thus was named myoepithelium-derived serine proteinase inhibitor (MEPI). No MEPI expression was detected in the malignant breast carcinomas. MEPI encodes a 405-aa precursor, including an 18-residue secretion signal with a calculated molecular mass of 46 kDa. The predicted sequence of the new protein shares 33% sequence identity and 58% sequence similarity to plasminogen activator inhibitor (PAI)-1 and PAI-2. To determine whether MEPI can modulate the in vivo growth and progression of human breast cancers, we transfected a full-length MEPI cDNA into human breast cancer cells and studied the orthotopic growth of MEPI-transfected vs. control clones in the mammary fat pad of athymic nude mice. Overexpression of MEPI inhibited the invasion of the cells in the in vitro invasion assay. When injected orthotopically into nude mice, the primary tumor volumes, axillary lymph node metastasis, and lung metastasis were significantly inhibited in MEPI-transfected clones as compared with controls. The expression of MEPI in myoepithelial cells may prevent breast cancer malignant progression leading to metastasis.

[Respiratory monitoring and high frequence jet ventilation (HFJV) in the treatment of severe chest injuries]

Twenty-eight patients with severe chest injuries were classified into 3 groups: fractures of rib, hemopneumothorax and lung injured. Their respiratory rate (RR), SpO2 and blood gas were analysed. The results showed that SpO2 and PaO2 in lung-injured group were the lowest and RR was the highest in the 3 groups. After HFJV, there was a significant rise in PaO2 and SpO2 (P < 0.05) and a gradual recovery of respiratory and pulse rates in lung-injured group. The results suggest that respiratory monitoring is important for patients with chest injuries and HFJV may be used as an effective ventilation method for treating patients with severe chest injuries.

Cloning of a 2.5 kb murine bone sialoprotein promoter fragment and functional analysis of putative Osf2 binding sites

Bone sialoprotein (BSP) is an extracellular matrix protein that is intimately associated with the process of biomineralization. Osf2, a member of the Cbf/runt family of transcription factors, is required for the development of osteoblasts in vivo and has been reported to stimulate the transcription of BSP when overexpressed in mesenchymal cell lines. To investigate the role of Osf2 in BSP expression, we cloned a 2.5 kb fragment of a 5' untranscribed sequence from the murine BSP gene and evaluated it for putative Osf2 binding sites. This promoter, which was able to direct 5- to 10-fold higher levels of luciferase reporter expression in osteoblastic cells than in nonbone cell lines, contains two consensus core binding sites for members of the Cbf/runt family. One, at -61 relative to the start of transcription, is within a region having 75% overall sequence identity with the rat and human BSP promoters. The other is located at -1335, outside this highly conserved region. Neither site is completely conserved in the rat or human sequences. Only the -1335 site was able to bind a protein in nuclear extracts of osteoblastic cells, and this protein was identified as Osf2. Despite this in vitro binding ability, we detected no significant enhancer activity in the -1335 element when placed in front of a minimal osteocalcin promoter driving a luciferase reporter gene in osteoblastic cells nor any loss in transcriptional activity of a 5' promoter deletion which eliminated this element as compared with the full-length 2.5 kb promoter. These results suggest that Osf2 binding to the BSP promoter is not essential for its osteoblast-selective expression.

Gene expression profiles in HTLV-I-immortalized T cells: deregulated expression of genes involved in apoptosis regulation

Human T-cell leukemia virus type I (HTLV-I) is the etiologic agent of adult T-cell leukemia, an acute and often fatal T-cell malignancy. A key step in HTLV-I-induced leukemigenesis is induction of abnormal T-cell growth and survival. Unlike antigen-stimulated T cells, which cease proliferation after a finite number of cell division, HTLV-I-infected T cells proliferate indefinitely (immortalized), thus facilitating occurrence of secondary genetic changes leading to malignant transformation. To explore the molecular basis of HTLV-I-induced abnormal T-cell survival, we compared the gene expression profiles of normal and HTLV-I-immortalized T cells using 'gene array'. These studies revealed a strikingly altered expression pattern of a large number of genes along with HTLV-I-mediated T-cell immortalization. Interestingly, many of these deregulated genes are involved in the control of programmed cell death or apoptosis. These findings indicate that disruption of the cellular apoptosis-regulatory network may play a role in the HTLV-I-mediated oncogenesis.

[Pathogenetic effect of platelet activating factor on enterogenic endotoxemia after burn]

OBJECTIVE

To investigate the effects of platelet activating factor (PAF) on the occurrence of enterogenic endotoxemia after burn.

METHODS

The relationship between changes of PAF and enterogenic endotoxima was observed on a model of rats with 30% TBSA III degree burn.

RESULTS

The intestinal permeability and plasma endotoxin were significantly elevated and were positively correlated with the increase of PAF in the intestinal tissue and blood. PAF antagonist treatment significantly decreased the intestinal permeability and the levels of plasma endotoxin. After intravenous injection of enogenous PAF to healthy rats, the intestinal permeability and plasma endotoxin were also markedly increased, which was significantly depended on the dose of PAF.

CONCLUSION

PAF is one of the important factors for the occurrence of postburn enterogenic endotoximia.

[The relationship between obstructive sleep apnea and gastroesophageal reflux and the effect of antireflux therapy]

OBJECTIVE

To evaluate the relationship between gastroesophageal reflux (GER) and obstructive sleep apnea (OSA) and the effect of combined therapy with cisapride and omeprazole.

METHODS

24-hour esophageal pH and manometric monitoring and polysomnography (PSG) were performed in 18 patients with snoring, daytime sleepiness and acid reflux, heartburn and regurgitation. Cisapride 10 mg qid and omeprazole 20 mg q12h were given to patients with GER and OSA. these tests were repeated on the 7th day.

RESULTS

7 of the 18 patients with OSA had severe GER. All except one had daytime GER as well as nocturnal GER. Nocturnal recordings were analyzed and it was found that esophageal pH below 4.0 was frequently followed by swallow action (58.6%, control = 20.6%, P < 0.05), gross body movement (18.6%, control = 4.8%, P < 0.05) and arousal (26.8%, control = 16.8%, P < 0.05). The mean lowest esophageal pressure [(-15.2 +/- 9.6) mmHg] before and [(-18.6 +/- 10.1) mmHg] after the drops of pH were significantly lower than that during control periods [(-10.6 +/- 8.1) mmHg, P < 0.005]. After antireflux therapy, there was dramatically improvement in total apnea time [from (52.7 +/- 27.1) to (21.6 +/- 21.2) minutes, P < 0.002)] and apnea hypopnea index (AHI) [from (38.9 +/- 17.6) to (15.2 +/- 12.3) No./h, P < 0.002].

CONCLUSION

GER is a predisposing factor for OSA, they may coexist and aggravate each other. Combined therapy with cisapride and omeprazole is a new, simple and effective method for GER with OSA.

Role of the alpha2-integrin in osteoblast-specific gene expression and activation of the Osf2 transcription factor

Extracellular matrix molecules such as type I collagen are required for the adhesion, migration, proliferation, and differentiation of a number of cell types including osteoblasts. Matrix components often affect cell function by interacting with members of the integrin family of cell surface receptors. Previous work showed that collagen matrix synthesis, induced by addition of ascorbic acid to cells, precedes and is essential for the expression of osteoblast markers and induction of the osteocalcin promoter in murine MC3T3-E1 cells. This later response requires OSE2, the promoter element recognized by Osf2 (also called Cbfa1/AML3/PEBP2alphaA), a recently identified osteoblast-specific transcription factor. Osteoblasts express several integrins including alpha2beta1 which is a major receptor for type I collagen. This paper examines the role of the alpha2-integrin subunit in osteocalcin promoter activation and osteoblast differentiation. Disruption of alpha2-integrin-ECM interactions with a blocking antibody or DGEA peptide containing the cell-binding domain of type I collagen blocked activation of the mouse osteocalcin gene 2 promoter by ascorbic acid as well as induction of endogenous osteocalcin mRNA and mineralization. Furthermore, anti-alpha2-integrin blocking antibody or peptide reduced ascorbic acid-dependent binding of Osf2 to OSE2 without affecting levels of transcription factor mRNA. Time course studies revealed that ascorbic acid-dependent binding of Osf2 to OSE2 preceded increases in osteocalcin and bone sialoprotein expression and this increase in Osf2 binding was not accompanied by comparable changes in levels of transcription factor mRNA or protein. Taken together, these studies demonstrate that an alpha2-integrin-collagen interaction is required for activation of Osf2 and induction of osteoblast-specific gene expression. Furthermore, matrix signals may regulate Osf2 through a post-translational pathway or via an accessory factor.

Functional hierarchy between two OSE2 elements in the control of osteocalcin gene expression in vivo

Osteocalcin gene expression is initiated perinatally and is restricted to mature osteoblasts and odontoblasts. Because their pattern of expression is highly restricted, the osteocalcin genes are excellent tools to study osteoblast-specific gene expression. To define the mechanisms of osteocalcin cell-specific gene expression in vivo, we generated transgenic mice harboring deletion mutants of the promoter region of OG2, one of the mouse osteocalcin genes. We show here that only 647 base pairs of this promoter are sufficient to confer cell-specific and time-specific expression to a reporter gene in vivo. This promoter fragment contains two copies of OSE2. This osteoblast-specific cis-acting element binds Osf2, a recently characterized osteoblast-specific transcription factor (Ducy, P., Zhang, R., Geoffroy, V., Ridall, A. L., and Karsenty, G. (1997) Cell 89, 747-754). We also demonstrate that the proximal OSE2 element is critical to confer an osteoblast-specific, developmentally regulated pattern of expression to a reporter gene. The other OSE2 element, located more upstream and presenting a lower affinity for Osf2, affects only weakly OG2 promoter activity. These data demonstrate the crucial role of Osf2 in controlling osteocalcin gene expression. Since osteocalcin synthesis is a hallmark of the differentiated osteoblast phenotype, these results suggest that, beyond its developmental function, Osf2 is also required for the maintenance of the osteoblast phenotype postnatally.

Conformational changes in the crystal structure of rat glutathione transferase M1-1 with global substitution of 3-fluorotyrosine for tyrosine

The structure of the tetradeca-(3-fluorotyrosyl) M1-1 GSH transferase (3-FTyr GSH transferase), a protein in which tyrosine residues are globally substituted by 3-fluorotyrosines has been determined at 2.2 A resolution. This variant was produced to study the effect on the enzymatic mechanism and the structure was undertaken to assess how the presence of the 3-fluorotyrosyl residue influences the protein conformation and hence its function. Although fluorinated amino acid residues have frequently been used in biochemical and NMR investigations of proteins, no structure of a protein that has been globally substituted with a fluorinated amino acid has previously been reported. Thus, this structure represents the first crystal structure of such a protein containing a library of 14 (28 crystallographically distinct) microenvironments from which the nature of the interactions of fluorine atoms with the rest of the protein can be evaluated. Numerous conformational changes are observed in the protein structure as a result of substitution of 3-fluorotyrosine for tyrosine. The results of the comparison of the crystal structure of the fluorinated protein with the native enzyme reveal that conformational changes are observed for most of the 3-fluorotyrosines. The largest differences are seen for residues where the fluorine, the OH, or both are directly involved in interactions with other regions of the protein or with a symmetry-related molecule. The fluorine atoms of the 3-fluorotyrosine interact primarily through hydrogen bonds with other residues and water molecules. In several cases, the conformation of a 3-fluorotyrosine is different in one of the monomers of the enzyme from that observed in the other, including different hydrogen-bonding patterns. Altered conformations can be related to differences in the crystal packing interactions of the two monomers in the asymmetric unit. The fluorine atom on the active-site Tyr6 is located near the S atom of the thioether product (9R,10R)-9-(S-glutathionyl)-10-hydroxy-9,10-dihydrophenanthrene and creates a different pattern of interactions between 3-fluorotyrosine 6 and the S atom. Studies of these interactions help explain why 3-FTyr GSH transferase exhibits spectral and kinetic properties distinct from the native GSH transferase.

NF-kappaB-inducing kinase and IkappaB kinase participate in human T-cell leukemia virus I Tax-mediated NF-kappaB activation

The tax gene product of human T-cell leukemia virus I induces aberrant expression of various cellular genes, which contributes to transformation of host cells. Induction of many Tax target genes is mediated through transcription factor NF-kappaB. Here we show that Tax triggers activation of cellular protein kinases, IkappaB kinase alpha (IKKalpha) and IKKbeta, which phosphorylate the NF-kappaB inhibitory protein IkappaB alpha, resulting in its degradation and NF-kappaB activation. Constitutive IKK activation occurs in both Tax-transfected and human T-cell leukemia virus I-infected T cells. We further demonstrate that Tax-mediated NF-kappaB signaling also requires the NF-kappaB-inducing kinase (NIK). Consistently, inactive forms of either IKKs or NIK attenuate Tax-mediated NF-kappaB activation. Therefore, Tax activates NF-kappaB by targeting cellular signaling molecules, including both IKKs and NIK.

Enzymes harboring unnatural amino acids: mechanistic and structural analysis of the enhanced catalytic activity of a glutathione transferase containing 5-fluorotryptophan

The catalytic characteristics and structure of the M1-1 isoenzyme of rat glutathione (GSH) transferase in which all four tryptophan residues in each monomer are replaced with 5-fluorotryptophan are described. The fluorine-for-hydrogen substitution does not change the interaction of the enzyme with GSH even though two tryptophan residues (Trp7 and Trp45) are involved in direct hydrogen-bonding interactions with the substrate. The rate constants for association and dissociation of the peptide, measured by stopped-flow spectrometry, remain unchanged by the unnatural amino acid. The 5-FTrp-substituted enzyme exhibits a kcat of 73 s-1 as compared to 18 s-1 for the native enzyme toward 1-chloro-2,4-dinitrobenzene. That the increase in the turnover number is due to an enhanced rate of product release in the mutant is confirmed by the kinetics of the approach to equilibrium for binding of the product. The crystal structure of the 5-FTrp-containing enzyme was solved at a resolution of 2.0 A by difference Fourier techniques. The structure reveals local conformational changes in the structural elements that define the approach to the active site which are attributed to steric interactions of the fluorine atoms associated with 5-FTrp146 and 5-FTrp214 in domain II. These changes appear to result in the enhanced rate of product release. This structure represents the first of a protein substituted with 5-fluorotryptophan.

Polymorphous crystallization and diffraction of threonine deaminase from Escherichia coli

The biosynthetic threonine deaminase from Escherichia coli, an allosteric tetramer with key regulatory functions, has been crystallized in several crystal forms. Two distinct forms, both belonging to either space group P3121 or P3221, with different sized asymmetric units that both contain a tetramer, grow under identical conditions. Diffraction data sets to 2.8 A resolution (native) and 2. 9 A resolution (isomorphous uranyl derivative) have been collected from a third crystal form in space group I222.

Structure and control of pyridoxal phosphate dependent allosteric threonine deaminase

BACKGROUND

Feedback inhibition of biosynthetic threonine deaminase (TD) from Escherichia coli provided one of the earliest examples of protein-based metabolic regulation. Isoleucine, the pathway end-product, and valine, the product of a parallel pathway, serve as allosteric inhibitor and activator, respectively. This enzyme is thus a useful model system for studying the structural basis of allosteric control mechanisms.

RESULTS

We report the crystal structure of TD at 2.8 A resolution. The tetramer has 222 symmetry, with C-terminal regulatory domains projecting out from a core of catalytic PLP-containing N-terminal domains. The subunits, and especially the regulatory domains, associate extensively to form dimers, which associate less extensively to form the tetramer. Within the dimer, each monomer twists approximately 150 degrees around a thin neck between the domains to place its catalytic domain adjacent to the regulatory domain of the other subunit.

CONCLUSIONS

The structure of TD and its comparison with related structures and other data lead to the tentative identification of the regulatory binding site and revealed several implications for the allosteric mechanism. This work prepares the way for detailed structure/function studies of the complex allosteric behaviour of this enzyme.

A preliminary clinical study of bifidobacteria preparation on the treatment of diarrhea in severely burned patients

OBJECTIVE

To investigate the role of bifidobacteria preparation in the prevention of diarrhea in severely burned patients.

METHODS

Forty-three severely burned patients who were inflicted by diarrhea were included in this study. The changes of intestinal microflora were observed.

RESULTS

The intestinal flora of all patients with diarrhea changed greatly before treatment. The proportions of bifidobacteria and bacteroid decreased significantly, whereas those of aerobe and Candida increased relatively. The ratio of anaerobe to aerobe decreased. As a result, the patients' intestinal flora were distorted. After six days treatment of bifidobacteria, diarrhea in most patients ceased and the intestinal microflora restored.

CONCLUSION

Bifidobacteria feeding plays an important role in restoring intestinal microflora and stopping diarrhea in severely burned patients.

Comparison of structural stabilities of prostaglandin H synthase-1 and -2

There are two known isoforms of prostaglandin H synthase (PGHS), a key enzyme in the conversion of arachidonic acid to bioactive prostanoids. The "constitutive" isoform, PGHS-1, is thought to have housekeeping functions, and the "inducible" isoform, PGHS-2, has been implicated in cellular responses to cytokines. The two isoforms have high sequence conservation in the cyclooxygenase active site and quite similar crystallographic structures, but differ markedly in their interactions with many cyclooxygenase substrates and inhibitors. We have evaluated the stability of the overall folding, and of the active sites of ovine PGHS-1 and human PGHS-2 using denaturation with guanidinium hydrochloride (GdmHCl). Changes in hydrodynamic and cross-linking properties indicated a dimer --> monomer transition for both isoforms between 0.5 and 2 M GdmHCl; the monomers unfolded at higher GdmHCl levels. Changes in overall secondary and tertiary structure, measured by tryptophan fluorescence and circular dichroism, occurred in two phases for each isoform, with the transition between the phases at 0.2-0.5 M GdmHCl. Disruption of active site functions (cyclooxygenase, peroxidase, and cyclooxygenase inhibitor binding activities) began at GdmHCl levels below 0.2 M. The structural and functional changes were completely reversible up to about 2 M GdmHCl, they were more pronounced at lower protein levels, and they required lower GdmHCl levels for PGHS-2 than for PGHS-1. The results are consistent with a four-state denaturation process for both isoforms: native dimers --> inactive dimers --> compact monomers --> unfolded monomers. The first two steps are reversible for both isoforms; PGHS-2 undergoes the first and last steps more readily than PGHS-1. Thus, the structural stability of PGHS-2, both in the active site regions and in the subunits overall, is distinctly less than that of PGHS-1. These differences in structural stability may contribute to the isoforms' active site ligand selectivity.

p53 binds to a constitutively nucleosome free region of the mdm2 gene

The mdm2 oncogene is a p53 responsive gene which contains both a p53 independent and a p53 dependent promoter (P1 and P2 respectively). We have utilized ligation mediated PCR genomic footprinting in order to investigate the intra-nuclear binding of p53 to the mdm2 P2 promoter. The DNase I protection pattern in nuclei from murine cells lacking p53 has been compared to the protection pattern in cells containing a temperature sensitive p53-Val135. At 32 degrees C p53-Val135 assumes a wild-type conformation while at 37 degrees C this p53 is conformationally mutant. We observed clear wild-type p53 dependent protection of the putative p53 response elements (REs) as well as protection of the adjacent TATA box. Interestingly the protection pattern observed with purified wild-type p53 on naked DNA showed less nucleotide sequence protection than the protection observed to be p53 dependent in nuclei. Constitutive DNase I hypersensitivity at both the mdm2 P1 and P2 promoters was detected by indirect Southern blot analysis. DNase I hypersensitivity reflects altered chromatin conformations resulting, most likely, from the absence of nucleosomes. Taken together our findings suggest that the mdm2 P2 promoter is maintained in a nucleosome free state which is pre-primed for transcriptional activation by p53.

[Determination of the soluble non-starch polysaccharides in rice and wheat bran by gas chromatography]

Cereal polysaccharides can be broadly classified into two distinct and chemically well-defined types. They are the storage polysaccharides (alpha-glucan) and the structural polysaccharides starch (beta-glucan) which are usually called non-starch polysaccharides (NSP). The determination of soluble non-starch polysaccharides in rice and wheat bran by gas chromatography has been developed. The free sugars in the sample were extracted with 80% ethanol. The residue was hydrolyzed in an acetic acid buffer solution (pH 5.0) in the presence of amylase and amyloglucosidase to remove starch. The soluble NSP obtained was further hydrolyzed in the acidic condition to produce the corresponding monosaccharides which were derivatized to form alditol acetates for GC analysis with allose as the internal standard. The GC conditions were OV-1701 column (25 m x 0.3 mm) with temperature program from 195 degrees C to 225 degrees C and FID.

Structural characterization of arachidonyl radicals formed by prostaglandin H synthase-2 and prostaglandin H synthase-1 reconstituted with mangano protoporphyrin IX

A tyrosyl radical generated in the peroxidase cycle of prostaglandin H synthase-1 (PGHS-1) can serve as the initial oxidant for arachidonic acid (AA) in the cyclooxygenase reaction. Peroxides also induce radical formation in prostaglandin H synthase-2 (PGHS-2) and in PGHS-1 reconstituted with mangano protoporphyrin IX (MnPGHS-1), but the EPR spectra of these radicals are distinct from the initial tyrosyl radical in PGHS-1. We have examined the ability of the radicals in PGHS-2 and MnPGHS-1 to oxidize AA, using single-turnover EPR studies. One wide singlet tyrosyl radical with an overall EPR line width of 29-31 gauss (G) was generated by reaction of PGHS-2 with ethyl hydroperoxide. Anaerobic addition of AA to PGHS-2 immediately after formation of this radical led to its disappearance and emergence of an AA radical (AA.) with a 7-line EPR, substantiated by experiments using octadeuterated AA. Subsequent addition of oxygen resulted in regeneration of the tyrosyl radical. In contrast, the peroxide-generated radical (a 21G narrow singlet) in a Y371F PGHS-2 mutant lacking cyclooxygenase activity failed to react with AA. The peroxide-generated radical in MnPGHS-1 exhibited a line width of 36-38G, but was also able to convert AA to an AA. with an EPR spectrum similar to that found with PGHS-2. These results indicate that the peroxide-generated radicals in PGHS-2 and MnPGHS-1 can each serve as immediate oxidants of AA to form the same carbon-centered fatty acid radical that subsequently reacts with oxygen to form a hydroperoxide. The EPR data for the AA-derived radical formed by PGHS-2 and MnPGHS-1 could be accounted for by a planar pentadienyl radical with two strongly interacting beta-protons at C10 of AA. These results support a functional role for peroxide-generated radicals in cyclooxygenase catalysis by both PGHS isoforms and provide important structural characterization of the carbon-centered AA..

2,5-bis[4-(N-alkylamidino)phenyl]furans as anti-Pneumocystis carinii agents

The syntheses of 12 new 2,5-bis[4-(N-alkylamidino)phenyl]furans are reported. The interaction of these dicationic furans with poly(dA-dT) and with the duplex oligomer d(CGCGAATTCGCG)2 was determined by Tm measurements, and the effectiveness of these compounds against the immunosuppressed rat model of Pneumocystis carinii was evaluated. At the screening dose of 10 mumol/kg, 9 of the 14 N-alkylamidino furans described here are more active than the parent compound 1. Substitution of an alkyl group of the amidino nitrogen, except for in 9, 13, and 15, resulted in higher affinity for DNA than the parent compound as judged by the larger delta Tm values and suggests enhanced van der Waals interactions in the bis-amidine-DNA complex. Five of the compounds, 3, 5, 7, 10, and 12, yield cyst counts of less than 0.1% of control when administered at a dosage of 10 mumol/kg. Five compounds, 1, 6, 8, 10, and 12, show significant activity at a dosage of approximately 1 mumol/kg; 12 is the most active derivative, and it is approximately 100 times more effective than pentamidine in this animal model.

[Analysis of triacylglycerol composition of perilla oil by combination of non-aqueous reversed-phase high performance liquid chromatography with gas chromatography]

Perilla oil was verified to be a rich source of polyunsaturated fatty acid (PUFA). Its linolenic content is 64.82%, the highest in the plants. Its triacylglycerol (TAG) components were isolated and identified first time in this paper by a combination of non-aqueous reversed-phase high performance liquid chromatography (RP-HPLC) with gas chromatography (GC). The TAG of perilla oil were isolated by HPLC with a Zorbax ODS column (5 microm, 4.6 mm i.d. x 250 mm; Dupont, Inc) and differential refractometer. The eluent was acetone/acetonitrile (80:20, V/V) with flow rate of 1.0 mL/min. The TAG component acyl groups were converted to fatty acid methyl esters (FAME). The acyl constituents for each TAG were determined by GC analysis. Gas chromatography of FAMEs was performed with a AC20 Carbowax 20M column (30 m x 0.32 mm i.d.). Detector and injection port temperatures were 260 degrees C. Column temperature was programmed from 120 degrees C, 1 min initially hold, then 8 degrees C/min to 220 degrees C and finally hold for 10 min. Nitrogen was the carrier gas. FAMEs peaks were identified by comparison of their retention times with those of standards. The retention times of the palmitic, stearic, oleic, linoleic, n-nonadecanoic acid (internal standard) and linolenic FAMEs were 10.7, 13.0, 13.3, 13.8, 14.2 and 14.7 min respectively. Five main components were determined. They were LnLnLn (34.10%), LnLnL (13.22%), LnLL (6.22%), LnLnO (11.38%) and LnLnP (9.17%). The TAG contents were corrected from their fatty acids content. The combination of non-aqueous RP-HPLC with GC is a simple and rapid method for the analysis of oil TAG structure and is also very helpful for the identification of oil quality.

Comparison of prostaglandin H synthase isoform structures using limited proteolytic digestion

Prostaglandin H synthase (PGHS) catalyzes a key step in the biosynthesis of a variety of bioactive lipid mediators. The two known isoforms (PGHS-1 and -2) share about 60% amino acid identity, but exhibit distinct interactions with substrates, activators, and inhibitors. Ovine PGHS-1 has previously been shown to have a distinctive protease-sensitive site near Arg277; cleavage by trypsin, chymotrypsin, or proteinase K produces fragments of 33 and 38 kDa and loss of activity. The ovine PGHS-1 crystal structure shows Arg277 located in an exposed loop structure; homology modeling predicts similar loop structures for both human isoforms (hPGHS-1 and -2). We have used limited proteolytic digestion of recombinant hPGHS-1 and hPGHS-2 to probe their structures. Incubation of hPGHS-1 with either trypsin or proteinase K produced 33- and 38-kDa fragments and loss of activity. In contrast, incubation of hPGHS-2 with the same proteases led to cleavage of only a 2- to 3-kDa fragment, with no decrease in activity. Immunoblotting with site-specific antibodies demonstrated that the cleaved fragment originated from the hPGHS-2 C-terminus. Similar immunoblotting experiments indicated that trypsin did not attack the ovine PGHS-1 C-terminus. Mutagenesis was used to replace Pro263 of hPGHS-2 (corresponds to Arg277 of ovine PGHS-1) with arginine, inserting a potential trypsin site. Incubation of this P263R hPGHS-2 mutant with either trypsin or proteinase K resulted in cleavage near the C-terminus and retention of activity, just as with wild-type hPGHS-2. A peptide containing residues 259-268 of the P263R mutant was cleaved by trypsin at the same rate as a peptide corresponding to hPGHS-1 residues 272-281, demonstrating that the sequence differences were not responsible for the lack of tryptic cleavage at residue 263 in the hPGHS-2 mutant. Preincubation of hPGHS-2 with graded levels of guanidinium HCl before incubation with proteinase K did not produce large proteolytic fragments, indicating that the hPGHS-2 loop region was not selectively unfolding. The results point to two regions of significant structural difference between PGHS-1 and -2: the Arg277 loop, which is protease-sensitive in PGHS-1 but protease-resistant in PGHS-2, and the C-terminus, which is protease-sensitive in PGHS-2 but not in PGHS-1.

Antitumor activity of the novel human breast cancer growth inhibitor, mammary-derived growth inhibitor-related gene, MRG

A novel human tumor growth inhibitor was identified by differential cDNA sequencing. The predicted amino acid sequence of this tumor-suppressing factor has a significant sequence homology to mouse mammary-derived growth inhibitor and thus was named mammary-derived growth inhibitor-related gene (MRG). MRG was found to be expressed in normal and benign human breast tissues but not in breast carcinomas. In situ hybridization analysis demonstrated a stage-specific MRG expression as follows. MRG was barely detectable in breast carcinomas, showed partial and weak expression in benign hyperplasia, but was expressed at a high level in normal breast epithelial cells. To determine if MRG can modulate in vivo growth of human breast cancers, we transfected a full-length MRG cDNA into MDA-MB-231 human breast cancer cells and studied the orthotopic growth of MRG transfectants versus control transfectants in the mammary fat pad of athymic nude mice. Overexpression of MRG in human breast cancer cells significantly suppressed cell proliferation in vitro and tumor growth in an orthotopic nude mouse model. These results suggest that MRG has tumor-suppressing activity, and the loss of MRG expression may be involved in the development and progression of breast cancer.

Construction and screening of a multi-point site-specific mutant library of subtilisin E with a set of oligonucleotides

A mutant library of subtilisin E containing random combinations of various mutagenized sites was constructed by one-round mutagenesis with 15 mutagenic oligonucleotides. Mutants were screened through dot blot hybridization and DNA sequencing. A single-point mutant (Met 222Ala) and a three-point (Asn 76Asp/Asn109Ser/ I le 205/Cys) mutant gene from the library were expressed. The mutant proteins exhibited conspicuously improved resistance to oxidation and heat treatment, as reported before. The results show that the library is reliable and very useful for protease subtilisin E engineering.

Ascorbic acid-dependent activation of the osteocalcin promoter in MC3T3-E1 preosteoblasts: requirement for collagen matrix synthesis and the presence of an intact OSE2 sequence

Osteocalcin is a hormonally regulated calcium-binding protein made almost exclusively by osteoblasts. In normal cells, osteocalcin expression requires ascorbic acid (AA), an essential cofactor for osteoblast differentiation both in vivo and in vitro. To determine the mechanism of this regulation, subclones of MC3T3-E1 preosteoblasts were transiently transfected with 1.3 kb of the mouse osteocalcin gene 2 promoter driving expression of firefly luciferase. AA stimulated luciferase activity 20-fold after 4-5 days. This response was stereospecific to L-ascorbic acid and was only detected in MC3T3-E1 subclones showing strong AA induction of the endogenous osteocalcin gene. Similar results were also obtained in MC3T3-E1 cells stably transfected with the osteocalcin promoter. A specific inhibitor of collagen synthesis, 3,4-dehydroproline, blocked AA-dependent induction of promoter activity, indicating that regulation of the osteocalcin gene requires collagen matrix synthesis. Deletion analysis of the mOG2 promoter identified an essential region for AA responsiveness between -147 and -116 bp. This region contains a single copy of the previously described osteoblast-specific element, OSE2. Deletion and mutation of OSE2 in DNA transfection assays established the requirement for this element in the AA response. Furthermore, DNA-binding assays revealed that MC3T3-E1 cells contain OSF2, the nuclear factor binding to OSE2, and that binding of OSF2 to OSE2 is up-regulated by AA treatment. Taken collectively, our results indicate that an intact OSE2 sequence is required for the induction of osteocalcin expression by AA.

Analysis of hydroperoxide-induced tyrosyl radicals and lipoxygenase activity in aspirin-treated human prostaglandin H synthase-2

A hydroperoxide-induced tyrosyl radical has been proposed as a key cyclooxygenase intermediate for the "basal" isoform of prostaglandin H synthase (PGHS-1). In the present study with the "inducible" isoform (PGHS-2), hydroperoxide was also found to generate a radical in high yield, a wide singlet at g = 2.0058 (29 G peak to trough). Reaction of PGHS-2 with a tyrosine-modifying reagent, tetranitromethane (TNM), resulted in cyclooxygenase inactivation and a much narrower radical EPR signal (22 G peak to trough). Addition of a cyclooxygenase inhibitor, nimesulide, similarly resulted in a narrow PGHS-2 radical. In PGHS-1, cyclooxygenase inhibition by tyrosine nitration with TNM or by active site ligands leads to generation of a narrow EPR instead of a wide EPR, with both signals originating from authentic tyrosyl radicals, indicating that the hydroperoxide-induced radicals in PGHS-2 are also tyrosyl radicals. Treatment of PGHS-2 with aspirin (acetyl salicylic acid, ASA) was previously shown to result in acetylation of a specific serine residue, cyclooxygenase inhibition, and increased lipoxygenase activity. Acetylation of PGHS-1 by ASA, in contrast, inhibited both lipoxygenase and cyclooxygenase activity. We now have found the ASA-treated PGHS-2 radical to be indistinguishable from that in control PGHS-2. Addition of nimesulide to ASA-treated PGHS-2 inhibited the lipoxygenase and resulted in a narrow radical EPR like that seen in PGHS-2 treated with TNM or nimesulide alone. Retention of PGHS-2 oxygenase activity was thus associated with retention of the native radical, and loss of activity was associated with alteration of the radical. Both native and ASA-treated PGHS-2 produced only the R stereoisomer of 11- and 15-HETE, demonstrating that the lipoxygenase stereochemistry was not changed by ASA. Native and ASA-treated PGHS-2 had lipoxygenase K(m) values considerably higher than that of the control PGHS-2 cyclooxygenase. Taken together, these results suggest that the same PGHS-2 tyrosyl radical serves as the oxidant for both cyclooxygenase and lipoxygenase catalysis and that acetylation of PGHS-2 by ASA favors arachidonate binding in an altered conformation which results in abstraction of the pro-R hydrogen from C13 and formation of 11(R)- and 15(R)-HETE.

Identification of a breast cancer-specific gene, BCSG1, by direct differential cDNA sequencing

A high-throughput direct-differential cDNA sequencing approach was employed to identify genes differentially expressed in normal breast as compared with breast cancer. Approximately 6000 expressed sequence tags (ESTs) from cDNA libraries of normal breast and breast carcinoma were selected randomly and subjected to EST-sequencing analysis. The relative expression levels of more than 2000 unique EST groups were quantitatively compared in normal versus cancerous breast. Of many putative differentially expressed genes, a breast cancer-specific gene, BCSGC1, which was expressed in high abundance in a breast cancer cDNA library but scarcely in a normal breast cDNA library, was identified as a putative breast cancer marker. In situ hybridization analysis demonstrated stage-specific BCSG1 expression as follows: BCSG1 was undetectable in normal or benign breast lesions, showed partial expression in ductal carcinoma in situ, but was expressed at an extremely high level in advanced infiltrating breast cancer. The predicted amino acid sequence of BCSG1 gene has a significant sequence homology to the non-amyloid beta protein fragment of the Alzheimer's disease amyloid protein. BCSG1 overexpression may indicate breast cancer malignant progression from benign breast or in situ carcinoma to the highly infiltrating carcinoma.

A dual function activity-dependent, muscle-specific enhancer from rat nicotinic acetylcholine receptor delta-subunit gene

Nicotinic acetylcholine receptors (nAChR) mediate communication between nerve and muscle. The expression of these receptors increases dramatically during muscle development when myoblasts are fusing into multinucleated myotubes. The molecular mechanisms mediating this muscle developmental stage specific expression are not well understood. We report here the identification of nAChR delta-subunit promoter DNA sequences that differentially interact with nuclear proteins isolated from myoblasts, myotubes, and nonmuscle cells. The functional role these sequences play in mediating muscle-specific expression was explored using mutagenesis and enhancer assays. These studies resulted in the identification of a 47-bp muscle-specific enhancer that mediates increased expression of the nAChR delta-subunit gene during myotube formation. This enhancer contains an E-box and an element with similarity to the SV40 core enhancer (SVCE). Point mutations throughout this 47-bp enhancer showed that the E-box and the SVCE sequence are both necessary for conferring muscle-specific expression onto a heterologous promoter. Interestingly, this same DNA sequence also functions as an activity-dependent enhancer.

[A study on changes and its mechanisms of intestinal mucosal permeability after severe burn]

The changes in the intestinal mucosal permeability were observed by quantitatively assessing plasma to luminal clearance of 99mTc-labeled DTPA, and the influence of platelet activating factor (PAF) on it was investigated. The results showed that intestinal permeability was significantly elevated after severe burn and was positively correlated with increase in PAF in the intestinal tissue (r = 0.94, P < 0.01). PAF antagonist therapy could significantly attenuate postburn intestinal mucosal permeability. It is concluded that PAF is one of the important factors causing increased intestinal permeability after severe burn.

Identification and characterization of a 47 base pair activity-dependent enhancer of the rat nicotinic acetylcholine receptor delta-subunit promoter

Nicotinic acetylcholine receptor (nAChR) genes are regulated by muscle electrical activity. E-box sequences found in their promoters are necessary for this regulation. However, many muscle genes contain E-boxes, yet are not regulated by muscle depolarization. This suggests that other elements are necessary, perhaps working in conjunction with E-boxes, to confer depolarization-dependent control onto promoter activity. We have used direct DNA injection into muscle as an in vivo assay to identify and characterize these additional elements. Mutagenesis and expression assays identified multiple elements within the first 81 base pairs (bp) of the nAChR delta-subunit promoter that contribute to its regulation by muscle electrical activity. Within this 81 bp sequence, two regions of DNA were identified that were capable of conferring activity-dependent regulation onto a heterologous promoter. The stronger of these two putative enhancers was characterized further. It is a 47 bp sequence that contains an E-box along with sequences similar to the SV40 core enhancer and an SP1 site. Site-directed mutagenesis identified residues within each of these sequences that were necessary for enhancer activity. Furthermore, methylation interference DNA footprinting assays showed increased nuclear protein binding to sequences within both these enhancers after muscle denervation, and this pattern of binding was very similar to that observed with nuclear protein isolated from myotube extracts. These latter results suggest that similar mechanisms may mediate increased nAChR expression during muscle development and after muscle denervation.

[Changes of circulating Lps and cytokines in burned patients after anti-endotoxin therapy]

OBJECTIVE

Endotoxin as the inciting agent of cytokines and other mediators, whose high level expression correlates with the septic shock and MOF, has been the one of leading causes of death in ICU.

METHODS

For treating sepsis and MOF caused by endotoxin, the anti-lipid A of LPS antibody was used, 19 burned patients whose TBSA varied from 50% to 100% were divided into anti-LPS treatment group and nontreated group.

RESULTS

The levels of serum endotoxin, IL-6, IL-8, TNF and soluble IL-2R were lower obviously in patients of anti-LPS group than those of nontreated group (P < 0.05).

CONCLUSION

Clinical study surggests that anti-lipid A of LPS antibody can act as an therapeutic agent against gram-negative bacterin infection in burned patients.

[A study of the expression and localization of tumor necrosis factor mRNA in small intestine of rats after severe burn]

In this study, the dot blotting and in situ hybridization, collaborated with determination of contents of endotoxin and TNF in plasma, were used to study the expression and localization of TNF mRNA in the intestine. The results showed that, the expression of TNF mRNA in the small intestine increased rapidly and reached maximum at 6 h postburn, being 5.56 times higher than that of normal control. The TNF mRNA-producing cells in normal animal were mononuclear phagocytes located in lamina propria. After burn, the number of positive cells in lamina propria increased significantly, and the TNF gene-expressing cells were vascular endothelium. Many positive cells were found in the crypts of the intestine. It suggested that the expression of TNF correlated well with bacterial translocation in the early stage of burn. The mononuclear phagocytes and endothelial cells located in lamina propria and interstitial tissue were the chief TNF mRNA-producing cells in the intestine. The overproduction of TNF could provoke microvascular injury or induce the production of oxygen free radical to damage the gut mucosal barrier.

[Protective effect of lipid A monoclonal antibody against burn sepsis in rats]

A lipid A monoclonal antibody(mAb) was prepared and it was used to study its protective effect against burn sepsis. Wistar rats were inflicted with 30% TBSA third degress burn, and they were given LPS to mimic early sepsis after burn. The rats were divided randomly into burn with LPS, monoclonal antibody treatment, and control groups. The levels of endotoxin, tumor necrosis factor, light and electron microscopic studies of the morphological changes in the liver were studied. The results showed that the anti-lipid A monoclonal antibody demonstrated capacity to cross-react with several Gram-negative bacteria and their endotoxins. The mAb improved the survival rate of rats and decreased the levels of endotoxin and TNF as well as the liver damage significantly.

First-sphere and second-sphere electrostatic effects in the active site of a class mu gluthathione transferase

The activation of the thiol of glutathione (GSH) bound in the active site of the class mu glutathione transferase M1-1 from rat involves a hydrogen-bonding network that includes a direct (first-sphere) interaction between the hydroxyl group of Y6 and the sulfur of GSH and second-sphere interactions involving a hydrogen bond between the main-chain amide N-H of L12 and the hydroxyl group of Y6 and an on-face hydrogen bond between the hydroxyl group of T13 and the pi-electron cloud of Y6 (i.e., T13-OH---pi-Y6-OH--- -SG). The functions of these hydrogen bonds have been examined with a combination of site-specific mutagenesis and X-ray crystallography. The hydroxyl group of Y6 has a normal pKa of about 10 even though it is shielded from solvent and is in a largely hydrophobic environment. The apparent pKa of GSH in the binary Y6F.GSH complex is increased by 1.6 log units, and the reactivity of the enzyme-bound nucleophile is reduced. The catalytic properties of the Y6L mutant are identical to those of Y6F, suggesting that the weakly polar on-edge interaction between the aromatic ring and sulfur has no influence on catalysis. The refined three-dimensional structure of the Y6F mutant in complex with GSH shows no major structural perturbation of the protein other than a change in the coordination environment of the sulfur. Removal of the second-sphere influence of the on-face hydrogen bond between the hydroxyl groups T13 as in the T13V and T13A mutants elevates the pKa of enzyme-bound GSH by about 0.7 pKa units. Crystal structures of these mutants show that structural changes in the active site are minor and suggest that the changes in pKa of E.GSH are due to the presence or absence of the on-face hydrogen bond. The T13S mutant has a completely different side-chain hydrogen-bonding geometry than T13 in the native enzyme and catalytic properties similar to the T13A and T13V mutants consistent with the absence of an on-face hydrogen bond. The gamma-methyl group of T13 is essential in enforcing the on-face hydrogen bond geometry and preventing the hydroxyl group from forming more favorable conventional hydrogen bonds.