[Study on the related factors of intestinal obstruction after cesarean section]

Objective: To analyze the related factors of intestinal obstruction after cesarean section. Methods: From April 2009 to April 2019, 500 patients with cesarean section and postoperative intestinal obstruction in Beijing Maternity Hospital Affiliated to Capital Medical University were taken as the case group, and 500 patients without postoperative intestinal obstruction who underwent cesarean section on the same day as the case group were taken as the control group. The data of patients' general characteristics, pregnancy complications, blood routine and biochemical indexes, and operation related factors were collected to compare the differences between patients with intestinal obstruction and patients without intestinal obstruction. Multivariate logistic regression model was used to analyze the related factors of intestinal obstruction after cesarean section. Results: The age of 500 patients with intestinal obstruction after cesarean section was (33.3±4.2) years, and the age of 500 patients without intestinal obstruction after cesarean section was (31.6±3.9) years. The incidence of pregnancy complications in patients with intestinal obstruction was higher than that in patients without intestinal obstruction (all P<0.05). Multivariate analysis showed that preoperative anemia [OR(95%CI) of 5.318(1.522-18.580), P=0.009], postoperative low protein [OR(95%CI) of 0.376(0.143-0.993), P=0.048], intraoperative bleeding ≥500 ml [OR(95%CI) of 3.085(1.551-6.136), P=0.001],intraoperative adhesion [OR(95%CI) of 2.856(1.285-6.347), P=0.010] were the risk factor of intestinal obstruction after cesarean section. The intraoperative application of antiadhesion drugs [OR(95%CI) of 0.322(0.158-0.654), P=0.002] was the protective factor of intestinal obstruction after cesarean section. Conclusions: Patients with anemia and low protein have an increased risk of intestinal obstruction after cesarean section.

A Smartphone-Based Rapid Telemonitoring System for Ebola and Marburg Disease Surveillance

We have developed a digital and multiplexed platform for the rapid detection and telemonitoring of infections caused by Ebola and Marburg filoviruses. The system includes a flow cell assay cartridge that captures specific antibodies with microarrayed recombinant antigens from all six species of filovirus, and a smartphone fluorescent reader for high-performance interpretation of test results. Multiplexed viral proteins, which are expandable to include greater numbers of probes, were incorporated to obtain highest confidence results by cross-correlation, and a custom smartphone application was developed for data analysis, interpretation, and communication. The smartphone reader utilizes an opto-electro-mechanical hardware attachment that snaps at the back of a Motorola smartphone and provides a user interface to manage the operation, acquire test results, and communicate with cloud service. The application controls the hardware attachment to turn on LEDs and digitally record the optically enhanced images. Assay processing time is approximately 20 min for microliter amounts of blood, and test results are digitally processed and displayed within 15 s. Furthermore, a secure cloud service was developed for the telemonitoring of test results generated by the smartphone readers in the field. Assay system results were tested with sera from nonhuman primates that received a live attenuated EBOV vaccine. This integrated system will provide a rapid, reliable, and digital solution to prevent the rapid overwhelming of medical systems and resources during EVD or MVD outbreaks. Further, this disease-monitoring system will be useful in resource-limited countries where there is a need for dispersed laboratory analysis of recent or active infections.

[The effect of short-term exposure to ambient NO(2) on lung function and fractional exhaled nitric oxide in 33 chronic obstructive pulmonary disease patients]

Objectives: To investigate the effect of short-term exposure to ambient NO(2) has influence on lung function and fractional exhaled nitric oxide (FeNO) in chronic obstructive pulmonary disease (COPD) patients. Methods: A panel of doctor-diagnosed stable COPD patients (n=33) were recruited and repeatedly measured for lung function and FeNO from December 2013 to October 2014. The patients who lived in Beijing for more than one year and aged between 60 and 85 years old were included in the study. We excluded patients with asthma, bronchial tensor, lung cancer and other respiratory disorders other than chronic obstructive pulmonary disease and occupational exposure and chest trauma surgery patients. Because the frequency of each subject visiting to the hospital was different, a total of 170 times of lung function measurements and 215 times of FeNO measurements were conducted. At the same time, the atmospheric NO(2) data of Beijing environmental monitoring station near the residence of each patient during the study period were collected from 1 day to 7 days lag before the measurement. Effects of short-term NO(2) exposure on lung function and FeNO in COPD patients were estimated by linear mixed-effects models. Results: The subjects' forced vital capacity (FVC), forced expiratory volume in one second (FEV(1)), peak expiratory flow (PEF), and exhaled NO of subjects were (3.26±0.83) L, (1.66±0.61) L, (4.13±1.77) L/s, and (48.99±14.30) μg/m(3), respectively. The concentration of NO(2) was (70.3±34.2) μg/m(3) and the interquartile range (IQR) was 39.0 μg/m(3). Short-term exposure to NO(2) resulted in a significant decrease in FVC among COPD patients' which was most obvious in 2 days lag. Every quartile range increased in NO(2) (39 μg/m(3), 2 day) would cause a 1.84% (95%CI: -3.20%- -0.48%) reduction in FVC. The effects of exposure to higher concentration of NO(2) (≥58.0 μg/m(3)) on FVC estimate was -2.32% (95%CI: -4.15%- -0.48%)(P=0.02). No significant relevance of FeNO and NO(2) was observed in this study. Conclusions: Short term exposure to ambient NO(2) may bring down pulmonary function in COPD patients.

[Analysis of factors affecting vaginal birth after cesarean]

OBJECTIVE

To investigate the factors affecting the vaginal birth after cesarean (VBAC).

METHODS

Totaly 298 women who underwent trial of labor after cesarean section (TOLAC) from Jan 2015 to Dec 2015 were recruited from Beijing Obstetrics and Gynecology Hospital, FuXing Hospital, Tongzhou Maternal and Child Health Hospital of Beijing, the Second Affiliated Hospital of Chongqing Medical University and the People's Hospital of Chengyang District of Qingdao. The maternal age, the interval from the last cesarean section, the body mass index (BMI) before pregnancy, the weight gain during pregnancy, the way into labor, the Bishop score before labor, the gestational age and the birth weight of the neonate were recorded in a self-made form. The factors affecting VBAC were analyzed by univariate analysis and multivariable logistic regression.

RESULTS

(1)The incidence of VBAC, uterine rupture, postpartum hemorrhage and neonatal asphyxia were 70.5% (210/298), 2.7% (8/298), 9.4% (28/298) and 1.3% (4/298), respectively. No maternal death and perinatal death occurred. (2)The univariate analysis suggested that the maternal age, the BMI before pregnancy, the Bishop score before labor, the labor induction, the gestational age at delivery and the neonatal weight were factors affecting VBAC. The maternal age and the Bishop score before labor were significantly higher in the VBAC group than in the unsuccessful TOLAC group(P<0.05). While the BMI before pregnancy, the induction rate, the gestational weeks at delivery and the birth weight of the neonate were significantly lower in the VBAC group than in the unsuccessful TOLAC group (P<0.05). Multivariable logistic regression analysis showed that successful VBAC was affected by the maternal age, the BMI before pregnancy, the Bishop score before labor and the birth weight of the neonates(P<0.05).

CONCLUSION

The maternal age, the BMI before pregnancy, the Bishop score before labor and the birth weight of neonate are the main factors affecting VBAC.

Rate dependent of strength in metallic glasses at different temperatures

The correlation between the strength at the macroscale and the elastic deformation as well as shear cracking behavior at the microscale of bulk metallic glasses (BMGs) is investigated. The temperatures of 298 K and 77 K as well as the strain rate ranging from 10⁻⁶ s⁻¹ to 10⁻² s⁻¹ are applied to the BMGs, in which the mechanical responses of the BMGs are profiled through the compression tests. The yield strength is associated with the activation of the elementary deformation unit, which is insensitive to the strain rate. The maximum compressive strength is linked to the crack propagation during shear fracture process, which is influenced by the strain rate. The cryogenic temperature of 77 K significantly improves the yield strength and the maximum compressive strength of the BMGs.

A single arabinan chain is attached to the phosphatidylinositol mannosyl core of the major immunomodulatory mycobacterial cell envelope glycoconjugate, lipoarabinomannan

Lipoarabinomannan (LAM) is composed of a phosphatidylinositol anchor followed by a mannan followed by an arabinan that may be capped with various motifs including oligosaccharides of mannose. A related polymer, lipomannan (LM), is composed of only the phosphatidylinositol and mannan core. Both the structure and the biosynthesis of LAM have been studied extensively. However, fundamental questions about the branching structure of LM and the number of arabinan chains on the mannan backbone in LAM remain. LM and LAM molecules produced by three different glycosyltransferase mutants of Mycobacterium smegmatis were used here to investigate these questions. Using an MSMEG_4241 mutant that lacks the α-(1,6)-mannosyltransferase used late in LM elongation, we showed that the reducing end region of the mannan that is attached to inositol has 5-7 unbranched α-6-linked-mannosyl residues followed by two or three α-6-linked mannosyl residues branched with single α-mannopyranose residues at O-2. After these branched mannosyl residues, the α-6-linked mannan chain is terminated with an α-mannopyranose at O-2 rather than O-6 of the penultimate residue. Analysis of the number of arabinans attached to the mannan core of LM in two other mutants (ΔembC and ΔMSMEG_4247) demonstrated exactly one arabinosyl substitution of the mannan core suggestive of the arabinosylation of a linear LM precursor with ∼10-12 mannosyl residues followed by additional mannosylation of the core and arabinosylation of a single arabinosyl "primer." Thus, these studies suggest that only a single arabinan chain attached near the middle of the mannan core is present in mature LAM and allow for an updated working model of the biosynthetic pathway of LAM and LM.

AGO61-dependent GlcNAc modification primes the formation of functional glycans on α-dystroglycan

Dystroglycanopathy is a major class of congenital muscular dystrophy that is caused by a deficiency of functional glycans on α-dystroglycan (α-DG) with laminin-binding activity. A product of a recently identified causative gene for dystroglycanopathy, AGO61, acted in vitro as a protein O-mannose β-1, 4-N-acetylglucosaminyltransferase, although it was not functionally characterized. Here we show the phenotypes of AGO61-knockout mice and demonstrate that AGO61 is indispensable for the formation of laminin-binding glycans of α-DG. AGO61-knockout mouse brain exhibited abnormal basal lamina formation and a neuronal migration defect due to a lack of laminin-binding glycans. Furthermore, our results indicate that functional α-DG glycosylation was primed by AGO61-dependent GlcNAc modifications of specific threonine-linked mannosyl moieties of α-DG. These findings provide a key missing link for understanding how the physiologically critical glycan motif is displayed on α-DG and provides new insights on the pathological mechanisms of dystroglycanopathy.

BAD-lectins: boronic acid-decorated lectins with enhanced binding affinity for the selective enrichment of glycoproteins

The weak and variable binding affinities exhibited by lectin-carbohydrate interactions have often compromised the practical utility of lectin in capturing glycoproteins for glycoproteomic applications. We report here the development and applications of a new type of hybrid biomaterial, namely a boronic acid-decorated lectin (BAD-lectin), for efficient bifunctional glycoprotein labeling and enrichment. Our binding studies showed an enhanced affinity by BAD-lectin, likely to be mediated via the formation of boronate ester linkages between the lectin and glycan subsequent to the initial recognition process and thus preserving its glycan-specificity. Moreover, when attached to magnetic nanoparticles (BAD-lectin@MNPs), 2 to 60-fold improvement on detection sensitivity and enrichment efficiency for specific glycoproteins was observed over the independent use of either lectin or BA. Tested at the level of whole cell lysates for glycoproteomic applications, three different types of BAD-lectin@MNPs exhibited excellent specificities with only 6% overlapping among the 295 N-linked glycopeptides identified. As many as 236 N-linked glycopeptides (80%) were uniquely identified by one of the BAD-lectin@MNPs. These results indicated that the enhanced glycan-selective recognition and binding affinity of BAD-lectin@MNPs will facilitate a complementary identification of the under-explored glycoproteome.

Sweet-Heart - an integrated suite of enabling computational tools for automated MS2/MS3 sequencing and identification of glycopeptides

High efficiency identification of intact glycopeptides from a shotgun glycoproteomic LC-MS(2) dataset remains problematic. The prevalent mode of identifying the de-N-glycosylated peptides is littered with false positives and addresses only the issue of site occupancy. Here, we present Sweet-Heart, a computational tool set developed to tackle the heart of the problems in MS(2) sequencing of glycopeptide. It accepts low resolution and low accuracy ion trap MS(2) data, filters for glycopeptides, couples knowledge-based de novo interpretation of glycosylation-dependent fragmentation pattern with protein database search, and uses machine-learning algorithm to score the computed glyco and peptide combinations. Higher ranking candidates are then compiled into a list of MS(2)/MS(3) entries to drive subsequent rounds of targeted MS(3) sequencing of putative peptide backbone, allowing its validation by database search in a fully automated fashion. With additional fishing out of all related glycoforms and final data integration, the platform proves to be sufficiently sensitive and selective, conducive to novel glycosylation discovery, and robust enough to discriminate, among others, N-glycolyl neuraminic acid/fucose from N-acetyl neuraminic acid/hexose. A critical appraisal of its computing performance shows that Sweet-Heart allows high sensitivity comprehensive mapping of site-specific glycosylation for isolated glycoproteins and facilitates analysis of glycoproteomic data.

BIOLOGICAL SIGNIFICANCE

The biological relevance of protein site-specific glycosylation cannot be meaningfully addressed without first defining its pattern by direct analysis of glycopeptides. Sweet-Heart is a novel suite of computational tools allowing for automated analysis of mass spectrometry-based glycopeptide sequencing data. It is developed to accept ion trap MS2/MS3 data and uses a machine learning algorithm to score and rank the candidate peptide core and glycosyl substituent combinations. By eliminating the need for manual, labor-intensive, and subjective data interpretation, it facilitates high throughput shotgun glycoproteomic data analysis and is conducive to identification of unanticipated glycosylation, as demonstrated here with a recombinant EGFR.

In vivo regulation of steroid hormones by the Chst10 sulfotransferase in mouse

Chst10 adds sulfate to glucuronic acid to form a carbohydrate antigen, HNK-1, in glycoproteins and glycolipids. To determine the role of Chst10 in vivo, we generated systemic Chst10-deficient mutant mice. Although Chst10^−/− mice were born and grew to adulthood with no gross defects, they were subfertile. Uteri from Chst10^−/− females at the pro-estrus stage were larger than those from wild-type females and exhibited a thick uterine endometrium. Serum estrogen levels in Chst10^−/− females were higher than those from wild-type females, suggesting impaired down-regulation of estrogen. Because steroid hormones are often conjugated to glucuronic acid, we hypothesized that Chst10 sulfates glucuronidated steroid hormone to regulate steroid hormone in vivo. Enzymatic activity assays and structural analysis of Chst10 products by HPLC and mass spectrometry revealed that Chst10 indeed sulfates glucuronidated estrogen, testosterone, and other steroid hormones. We also identified an HPLC peak corresponding to sulfated and glucuronidated estradiol in serum from wild-type but not from Chst10 null female mice. Estrogen-response element reporter assays revealed that Chst10-modified estrogen likely did not bind to its receptor. These results suggest that subfertility exhibited by female mice following Chst10 loss results from dysregulation of estrogen. Given that Chst10 transfers sulfates to several steroid hormones, Chst10 likely functions in widespread regulation of steroid hormones in vivo.

Identification of the Mycobacterium marinum Apa antigen O-mannosylation sites reveals important glycosylation variability with the M. tuberculosis Apa homologue

The 45/47 kDa Apa, an immuno-dominant antigen secreted by Mycobacterium tuberculosis is O-mannosylated at multiple sites. Glycosylation of Apa plays a key role in colonization and invasion of the host cells by M. tuberculosis through interactions of Apa with the host immune system C-type lectins. Mycobacterium marinum (M.ma) a fish pathogen, phylogenetically close to M. tuberculosis, induces a granulomatous response with features similar to those described for M. tuberculosis in human. Although M.ma possesses an Apa homologue, its glycosylation status is unknown, and whether this represents a crucial element in the pathophysiology induced by M.ma remains to be addressed. To this aim, we have identified two concanavalin A-reactive 45/47 kDa proteins from M.ma, which have been further purified by a two-step anion exchange chromatography process. Advanced liquid chromatography-nanoESI mass spectrometry-based proteomic analyses of peptides, derived from either tryptic digestion alone or in combination with the Asp-N endoproteinase, established that M.ma Apa possesses up to seven distinct O-mannosylated sites with mainly single mannose substitutions, which can be further extended at the Ser/Thr/Pro rich region near the N-terminus. This opens the way to further studies focussing on the involvement and biological functions of Apa O-mannosylation using the M.ma/zebrafish model.

MS-based glycomic strategies for probing the structural details of polylactosaminoglycan chain on N-glycans and glycoproteomic identification of its protein carriers

Most MS-based glycomic and glycoproteomic analyses focus on identifying changes in terminal glyco-epitopes represented by sialylation and fucosylation at specific positions of the terminal N-acetyllactosamine units. Much less attention was accorded to the underlying linear or branched poly-N-acetyllactosamine extension from the N-glycan trimannosyl core other than a simple inference of its presence due to mass data and hence glycosyl compositional assignment. Using the EA.hy926 cell line derived from human umbilical vein endothelial cells (HUVEC), we have systematically investigated the MALDI- and ESI-MS-based methodologies for probing the structural details of endothelial polylactosaminoglycans at both MS and MS(2) levels in conjunction with the use of endo-β-galactosidase to identify branching motifs and initiation sites. We showed that the polylactosaminoglycan chains on the N-glycans of EA.hy926 were less sialylated and fucosylated but more extended and branched than those of human umbilical vein endothelial cells, thus demonstrating a fundamental glycomic difference. For EA.hy926 that was investigated in more details, its polylactosaminoglycan chains were shown to be not restricted to extending from a specific antenna including the biologically important 6-arm position. Finally, experimental conditions for glycopeptide enrichment by tomato lectin were further optimized, which led to identification of over 40 candidate endothelial membrane protein carriers of polylactosaminoglycans by proteomic analysis.

Glycoproteomics analysis to identify a glycoform on haptoglobin associated with lung cancer

Glycosylation is a common protein modification that is of interest in current cancer research because altered carbohydrate moieties are often found during cancer progress. A search for biomarkers in human lung cancer serum samples using glycoproteomic approaches identified fucosylated haptoglobin (Hp) significantly increased in serum of each subtype of lung cancer compared to normal donors. In addition, MS provided evidence of an increase of Hp fucosylation; the glycan structure was determined to be an α 2,6-linked tri-sialylated triantennary glycan containing α1,3-linked fucose attached to the four-linked position of the three-arm mannose of N-linked core pentasaccharide. These preliminary findings suggest that the specific glycoform of Hp may be useful as a marker to monitor lung cancer progression.

Manipulating nanoscale light fields with the asymmetric bowtie nano-colorsorter

We present a class of devices called Asymmetric Bowtie nano-Colorsorters. These devices are specifically engineered to not only capture and confine optical fields, but also to spectrally filter and steer them while maintaining nanoscale field distributions. We show that spectral properties and localized spatial mode distributions can be readily tuned by controlled asymmetry. Nano-Colorsorters can control light's spatial and spectral distributions at the nanoscale and thus significantly impact applications ranging from broadband light harvesting to ultrafast wavelength-selective photodetection.

Enabling techniques and strategic workflow for sulfoglycomics based on mass spectrometry mapping and sequencing of permethylated sulfated glycans

Sulfate modifications on terminal epitopes of N- and O-glycans have increasingly been implicated as critical determinants mediating a diverse range of biological recognition functions. To address these low abundance but important sulfated glycans, and the sulfoglycome in general, further development of enrichment strategies and enabling mass spectrometry (MS)-based mapping techniques are needed. In this report, we demonstrate that the sulfated glycans, with and without additional sialylation, can be successfully permethylated by the sodium hydroxide slurry method and be distinguished from phosphorylated glycans by virtue of this derivatization. In conjunction with simple microscale postderivatization fractionation steps, permethyl derivatives fully retaining the negatively charged sulfate moiety and separated from the nonsulfated ones, can be efficiently detected and sequenced de novo by advanced MS/MS in the positive-ion mode. In particular, we show that the highly sequence and linkage informative high energy collision induced dissociation (CID) MS/MS afforded by MALDI-TOF/TOF can be extended to sulfoglycomic applications. The sulfated parent ion selected for CID MS/MS was found to mostly retain the sulfate moiety and therefore allow efficient fragmentation via the usual array of glycosidic, cross ring, and concerted double cleavages. Collectively, the optimized strategy enables a high sensitivity detection and critical mapping of the sulfoglycome such as the one derived from lymph node tissues or cell lines in both negative and positive-ion modes. Novel sulfated epitopes were identified from a crude mouse lymph node preparation, which fully attested to the practical utility of the methodology developed.

Early diagnosis of polyomavirus type BK infection in tailoring immunosuppression for kidney transplant patients: screening with urine qualitative polymerase chain reaction assay

Polyomavirus type BK (BKV) nephropathy is increasingly a significant cause of graft dysfunction and even failure. Early diagnosis followed by reduction of immunosuppression has been associated with an improved prognosis. We screened 250 patients with the urine qualitative polymerase chain reaction (PCR) for BKV DNA. We followed with blood BKV PCR if the urine screen was positive and then reduced immunosuppression in viremic patients. One hundred ninety-nine patients (80%) had no viuria; 43 (17%) viuria; and 8 (3%) both viuria and viremia. Graft biopsy performed in three patients (1%) with viremia and impaired graft function all revealed BKV nephropathy. After 6 months of follow-up, seven out of eight viremic patients (88%) had negative repeat blood PCR and stabilized graft function. An early diagnosis of BKV infection with reduction of immunosuppression may reverse viremia and retard progression of BKV nephropathy. BKV screening by PCR assays should be considered in kidney transplant recipients, especially those with impaired graft function.

Distinctive characteristics of MALDI-Q/TOF and TOF/TOF tandem mass spectrometry for sequencing of permethylated complex type N-glycans

Concerted MALDI-MS profiling and CID MS/MS sequencing of permethylated glycans is one of the most effective approaches for high throughput glycomics applications. In essence, the identification of larger complex type N-glycans necessitates an unambiguous definition of any modification on the trimannosyl core and the complement of non-reducing terminal sequences which constitute the respective antennary structures. Permethylation not only affords analyses of both neutral and sialylated glycans at comparable ease and sensitivity but also yields more sequence-informative fragmentation pattern. Facile glycosidic cleavages directed mostly at N-acetylglucosamine under low energy CID, as implemented on a quadrupole/time-of-flight (Q/TOF) instrument, often afford multiple losses of the attached antenna resulting in characteristic ions related to the number of antennary branches on the trimannosyl core. Non-reducing terminal epitopes can be easily deduced but information on the linkage specific substituent on the terminal units is often missing. The high energy CID MS/MS afforded by TOF/TOF instrument can fill in the gap by giving an array of additional cross-ring and satellite ions. Glycosidic cleavages occurring specifically in concert with loss of 2-linked or 3-linked substituents provide an effective way to identify the branch-specific antennary extension. These characteristics are shown here to be effective in deriving the sequences of additionally galactosylated, sialylated and fucosylated terminal N-acetyllactosamine units and their antennary location. Together, a highly reproducible fragmentation pattern can be formulated to simplify spectral assignment. This work also provides first real examples of sequencing multiply sialylated complex type N-glycans by high energy CID on a TOF/TOF instrument.

Characterization of a Distinct Arabinofuranosyltransferase in Mycobacterium smegmatis

The D-arabinans in Mycobacterium are essential, extraordinarily complex entity comprised of d-arabinofuranose residues which are rarely found in nature. Despite the well-recognized importance of the mycobacterial arabinan, delineation of the arabinosylation process has been severely hampered due to lack of positively identified arabinosyltransferases. Identification of genes involved in arabinan biosynthesis entailed the use of ethambutol (EMB), a first-line antituberculosis agent that is known to inhibit cell wall arabinan synthesis. The three genes (embA, embB, and embC) encode novel membrane proteins, implicated as the only known mycobacterial arabinosyltransferases to this date. We have now adapted a multifaceted approach involving development of convenient arabinosyltransferase assay using novel synthetic acceptors to identify arabinosyltransferase/s that will be distinct from the Emb proteins. In our present work, Mycobacterium smegmatis mc(2) 155 (WTMsm) was used as a model to study the biosynthesis of cell wall arabinan. In an in vitro assay, we demonstrate that transfer of only alpha-Araf had occurred from decaprenylphosphoryl-D-arabinofuranose (DPA) on a newly synthesized branched acceptor [alpha-D-Araf](2)-3,5-alpha-D-Araf-(1-->5)-alpha-d-Araf-(1-->5)-alpha-D-Araf with an octyl aglycon. Higher molecular weight (up to Ara(10)) oligomers were also detected in a parallel reaction using cold phosphoribosepyrophosphate (pRpp). Matrix-assisted laser desorption ionization time-of-flight tandem mass spectrometry (MALDI-TOF MS/MS) analysis of these products revealed that isomeric products were formed and initiation and elongation of arabinan can occur either on the 5-arm or 3-arm of the branched 3,5-alpha-D-Araf. Individual embA, embB, and embC knockout strains retained this alpha-1,5 arabinosyltransferase activity, and the activity was partially inhibited by ethambutol. This particular enzyme function is distinct from the function of the Emb proteins.

Analysis of protein-linked glycosylation in a sperm-somatic cell adhesion system

Murine sperm initiate fertilization by binding to the specialized extracellular matrix of their complementary eggs, known as the zona pellucida. On the basis of data reported in this study, mouse sperm also bind to rabbit erythrocytes with higher affinity than they do to murine eggs. This unusual interaction between a germ cell and a somatic cell ("sperm-somatic cell adhesion system") is also carbohydrate dependent based on its sensitivity to mild periodate oxidation. To determine what types of carbohydrate sequences could be involved in this interaction, the protein-linked oligosaccharides of rabbit erythrocytes were sequenced using novel matrix-assisted laser desorption/ionization time-of-flight tandem mass spectrometry methods that enabled the analysis of individual components up to m/z 9000. The N-glycans are primarily complex biantennary and triantennary types terminated with Galalpha1-3Gal sequences. The majority of these oligosaccharides also possess one antenna consisting of a highly branched polylactosamine-type sequence that is also associated with many glycosphingolipids that coat rabbit erythrocytes. These erythrocytes also express Core 1 and Core 2 O-glycans terminated primarily with Galalpha1-3Gal sequences and to a lesser extent sialic acid. These results confirm that rabbit erythrocytes and mouse eggs present very different types of carbohydrate sequences on their surfaces. However, oligosaccharides terminated with beta1-6-linked N-acetyllactosamine or its alpha1-3 galactosylated analog are expressed on both the mouse zona pellucida and this somatic cell type. The far more abundant presentation of such sequences on rabbit erythrocytes compared with murine eggs could explain why mouse sperm display such exceptional affinity for this somatic cell type.

Sequencing of oligoarabinosyl units released from mycobacterial arabinogalactan by endogenous arabinanase: identification of distinctive and novel structural motifs

The mycobacterial D-arabinofuran is a common constituent of both cell wall mycolyl-arabinogalactan (AG) and the associated lipoarabinomannan (LAM), and is thus accorded critical structural and immunological roles. Despite a well-recognized importance, progress in understanding its full structural characteristics beyond the nonreducing terminal motifs has hitherto been limited by available analytical tools. An endogenous arabinanase activity recently isolated from Mycobacterium smegmatis was previously shown to be capable of releasing large oligoarabinosyl units from AG. Advanced tandem mass spectrometry utilizing both low and high energy collision induced dissociation now afforded a facile way to map and directly sequence the digestion products which were dominated by distinctive Ara18 and Ara19 structural units, together with Ara7 and lesser amount of Ara11 and Ara12. Significantly, evidence was obtained for the first time which validated the linkages and branching pattern of the previously inferred Ara22 structural motif of AG, on which the preferred cleavage sites of the novel arabinanase could be localized. The established linkage-specific MS/MS fragmentation characteristics further led to identification of a galactosamine substituent on the C2 position of a portion of the internal 3,5-branched Ara residue of the AG of Mycobacterium tuberculosis, but not that of the nonpathogenic, fast growing M. smegmatis.

Role of VraSR in antibiotic resistance and antibiotic-induced stress response in Staphylococcus aureus

Exposure of Staphylococcus aureus to cell wall inhibitors induces massive overexpression of a number of genes, provided that the VraSR two-component sensory regulatory system is intact. Inactivation of vraS blocks this transcriptional response and also causes a drastic reduction in the levels of resistance to beta-lactam antibiotics and vancomycin. We used an experimental system in which the essential cell wall synthesis gene of S. aureus, pbpB, was put under the control of an isopropyl-beta-d-thiogalactopyranoside-inducible promoter in order to induce reversible perturbations in cell wall synthesis without the use of any cell wall-active inhibitor. Changes in the level of transcription of pbpB were rapidly followed by parallel changes in the vraSR signal, and the abundance of the pbpB transcript was precisely mirrored by the abundance of the transcripts of vraSR and some additional genes that belong to the VraSR regulon. Beta-lactam resistance in S. aureus appears to involve a complex stress response in which VraSR performs the critical role of a sentinel system capable of sensing the perturbation of cell wall synthesis and allowing mobilization of genes that are essential for the generation of a highly resistant phenotype. One of the sites in cell wall synthesis "sensed" by the VraSR system appears to be a step catalyzed by PBP 2.

Atomic-Scale Coupling of Photons to Single-Molecule Junctions

Spatial resolution at the atomic scale has been achieved in the coupling of light to single molecules adsorbed on a surface. Electron transfer to a single molecule induced by green to near-infrared light in the junction of a scanning tunneling microscope (STM) exhibited spatially varying probability that is confined within the molecule. The mechanism involves photo-induced resonant tunneling in which a photoexcited electron in the STM tip is transferred to the molecule. The coupling of photons to the tunneling process provides a pathway to explore molecular dynamics with the combined capabilities of lasers and the STM.

Design and characterization of a multimeric DNA binding protein using Sac7d and GCN4 as templates

The protein Sac7d belongs to a class of small chromosomal proteins from the hyperthermophilic archaeon Sulfolobus acidocaldarius. Sac7d is extremely stable to heat, acid, and chemical agents. This protein is a monomer and it binds DNA without any particular sequence preference, while inducing a sharp kink in the DNA. By appending a leucine-zipper-like helical peptide derived from the yeast transcriptional activator GCN4 to the C-terminal end of Sac7d, the modified monomers (denoted S7dLZ) are expected to interact with each other via hydrophobic force to form a parallel dimer. The recombinant S7dLZ was expressed in Escherichia coli and purified by heating and ion-exchange chromatography. The formation of dimer was detected by gel-filtration chromatography and chemical cross-link. The results of surface plasmon resonance and circular dichroism experiments showed that the DNA-binding capacity was retained. Furthermore, X-ray diffraction analysis of single crystals of S7dLZ in complex with DNA decamer CCTATATAGG showed that the leucine-zipper segments of S7dLZ were associated into an antiparallel four-helix bundle. There are two DNA fragments bound to each S7dLZ tetramer in the crystal. This model works as a successful template that endows protein a new function without losing original properties.

Tunneling rates in electron transport through double-barrier molecular junctions in a scanning tunneling microscope

The scanning tunneling microscope enables atomic-scale measurements of electron transport through individual molecules. Copper phthalocyanine and magnesium porphine molecules adsorbed on a thin oxide film grown on the NiAl(110) surface were probed. The single-molecule junctions contained two tunneling barriers, vacuum gap, and oxide film. Differential conductance spectroscopy shows that electron transport occurs via vibronic states of the molecules. The intensity of spectral peaks corresponding to the individual vibronic states depends on the relative electron tunneling rates through the two barriers of the junction, as found by varying the vacuum gap tunneling rate by changing the height of the scanning tunneling microscope tip above the molecule. A simple, sequential tunneling model explains the observed trends.

Control of relative tunneling rates in single molecule bipolar electron transport

The influence of relative electron tunneling rates on electron transport in a double-barrier single-molecule junction is studied. The junction is defined by positioning a scanning tunneling microscope tip above a copper phthalocyanine molecule adsorbed on a thin oxide film grown on the NiAl(110) surface. By tuning the tip-molecule separation, the ratio of tunneling rates through the two barriers, vacuum and oxide, is controlled. This results in dramatic changes in the relative intensities of individual conduction channels, associated with different vibronic states of the molecule.

Metabolism of territrem a in liver microsomes from wistar rats: 2. Sex differences and regulation with gonadal hormones and phenobarbital

The aim of the present study was to assess the effects of sex difference on metabolism of territrem A (TRA) by liver microsomes from 7-wk-old Wistar rats. Metabolism of TRA to 2-dihydro-4beta-demethylterritrem A (MA2) through 4beta-hydroxymethyl-4beta-demethylterritrem A (MA1) and 4beta-oxo-4beta-demethylterritrem A (MAX) was observed in intact male rats. However, in intact female rats only MA1 was formed, although the amount of MA, formed in females was much less than in males. Phenobarbital pretreatment enhanced this step and was not affected by gonadectomy. In the gonadectomized rats of both sexes, MA2 was formed from TRA when the animals were further treated by testosterone and was significantly enhanced by treatment with phenobarbital. However, estradiol treatment or estradiol in combination with phenobarbital treatment did not affect MA2 formation from TRA in gonadectomized rats.

Metabolism of territrem a by liver microsomes of Wistar rats: identification of the metabolites and their metabolic sequence

The metabolism of territrem A (TRA) was investigated in liver microsomes of male Wistar rats. The results indicated that three metabolites were produced from TRA and these metabolic reactions were inhibited by metyrapone, an inhibitor of cytochrome P-450. Based on analysis by high-performance liquid chromatography (HPLC), mass, and nuclear magnetic resonance (NMR) spectroscopic techniques, the structure of these metabolites were identified as 4beta-hydroxymethyl-4beta-demethylterritrem A (MA1), 4beta-oxo-4beta-demethylterritrem A (MAX), and 2-dihydro-4beta-demethylterritrem A (MA2). It was proposed that reactions proceeded by three sequential oxidative reactions in the pyran moiety of TRA: first, hydroxylation at the 4beta-C methyl group of TRA to form MA1; second, oxidation at the 4beta hydroxyl group of MA, to form MAX; and third, decarbonylation at the 4beta-C oxo group of MAX to form MA2.

Recruitment of the mecA gene homologue of Staphylococcus sciuri into a resistance determinant and expression of the resistant phenotype in Staphylococcus aureus

Strains of methicillin-resistant Staphylococcus aureus (MRSA) have become the most important causative agents of hospital-acquired diseases worldwide. The genetic determinant of resistance, mecA, is not a gene native to S. aureus but was acquired from an extraspecies source by an unknown mechanism. We recently identified a close homologue of this gene in isolates of Staphylococcus sciuri, a taxonomically primitive staphylococcal species recovered most frequently from rodents and primitive mammals. In spite of the close sequence similarity between the mecA homologue of S. sciuri and the antibiotic resistance determinant mecA of S. aureus, S. sciuri strains were found to be uniformly susceptible to beta-lactam antibiotics. In an attempt to activate the apparently "silent" mecA gene of S. sciuri, a methicillin-resistant derivative, K1M200 (for which the MIC of methicillin is 200 microg/ml), was obtained through stepwise exposure of the parental strain S. sciuri K1 (methicillin MIC of 4 microg/ml) to increasing concentrations of methicillin. DNA sequencing of the mecA homologue from K1M200 revealed the introduction of a point mutation into the -10 consensus of the promoter: the replacement of a thymine residue at nucleotide 1577 in the susceptible strain K1 by adenine in the resistant strain K1M200, which was accompanied by a drastic increase in transcription rate and the appearance of a new protein that reacted with monoclonal antibody prepared against the penicillin-binding protein 2A (PBP2A), i.e., the gene product of S. aureus mecA. Transduction of mecA from K1M200 (cloned into a plasmid vector) into a methicillin-susceptible S. aureus mutant resulted in a significant increase of methicillin resistance (from a methicillin MIC of 4 micro/ml to 12 and up to 50 microg/ml), the appearance of a low-affinity PBP detectable by the fluorographic assay, and the production of a protein that reacted in a Western blot with monoclonal antibody to PBP2A. Antibiotic resistance and the protein products disappeared upon removal of the plasmid-borne mecA homologue. The observations support the proposition that the mecA homologue ubiquitous in the antibiotic-susceptible animal species S. sciuri may be an evolutionary precursor of the methicillin resistance gene mecA of the pathogenic strains of MRSA.

Genetic organization of the downstream region of the mecA element in methicillin-resistant Staphylococcus aureus isolates carrying different polymorphisms of this region

We describe here the genetic organization of the mec element downstream of the mecA gene in 34 different methicillin-resistant Staphylococcus aureus (MRSA) clinical isolates carrying 13 of the most frequent polymorphisms of mecA and representing the major epidemic clones of MRSA. All polymorphisms carried three common genetic elements: the hypervariable region, a copy of IS431, and a unique 2-kb sequence (downstream constant segment, or dcs) for which no homologous sequences are found in data banks. Polymorphisms of the downstream region were shown to be caused by the presence of linearized plasmids flanked by insertion sequences (pUB110, pT181, and pI258) and the autonomous insertion sequence IS256.

Molecular cloning and DNA sequencing of the Staphylococcus aureus UDP-N-acetylmuramyl tripeptide synthetase (murE) gene, essential for the optimal expression of methicillin resistance

The Tn551 insertion in mutant RUSA235 of a highly methicillin resistant Staphylococcus aureus strain results in drastic reduction in the level of methicillin resistance and abnormalities, both in the composition of the peptidoglycan and of the cell wall precursor pool. Cloning and sequencing of the inactivated gene indicates that it is the murE gene of Staphylococcus aureus.

The Staphylococcus aureus transposon Tn551: complete nucleotide sequence and transcriptional analysis of the expression of the erythromycin resistance gene

The complete nucleotide sequence of Staphylococcus aureus transposon Tn551 was determined. The 5,266-bp sequence encoded five putative proteins. Comparison of the nucleotide sequence of Tn551 with that of the enterococcal transposon Tn917 showed that the two transposons were 99.8% identical and differed only at 11 positions along the entire sequence. The genetic organization of Tn551 was also identical to that of Tn917. Northern analysis of RNA prepared from a staphylococcal strain bearing Tn551 displayed three erm-associated transcripts that were constitutively produced. Mapping of the 5' ends of the transcripts by primer extension suggested that the constitutive transcription of erm was initiated from a nucleotide located 5 bp downstream of ORF1. A second set of three erythromycin-inducible transcripts was also detected and these showed a pattern similar to that described for Tn917. A simple and rapid method is described for the use of the Tn551 sequence information in sequencing transposon-inactivated staphylococcal genes.

Inactivation of the methicillin resistance gene mecA in vancomycin-resistant Staphylococcus aureus

Acquisition of high-level resistance to vancomycin in the laboratory mutant VM50 (vancomycin MIC increased from 1.5 to 100 microg/ml) was accompanied by the appearance of a heterogeneous phenotype and a virtual loss in methicillin resistance: in most cells of cultures of VM50 the methicillin MIC of the parental strain was reduced from 800 to 1.5 microg/ml with only a subpopulation (10(-5)) retaining methicillin resistance at near the parental level (MIC of 400 microg/ml). Interestingly, the vancomycin MIC of this subpopulation was less (25 microg/ml) than that of VM50 (100 microg/ml). A similar antagonism between methicillin and vancomycin resistance levels was observed upon introduction of an intact mecA into VM50 on a plasmid vector: methicillin resistance of the majority of cells increased from 1.5 to 100 microg/ml while the vancomycin MIC declined from 100 to 12/25 microg/ml. Membrane preparations from mutant VM50 showed no detectable penicillin-binding protein (PBP) 2A by the fluorographic assay. Sequencing of the mecA gene resident in mutant VM50 indicated the presence of a 19-bp duplication between nucleotide residues 280-298, leading to the generation of a stop codon TAA starting at nucleotide position 286.

Antibiotic resistance as a stress response: complete sequencing of a large number of chromosomal loci in Staphylococcus aureus strain COL that impact on the expression of resistance to methicillin

Tn551 inactivation has identified several determinants--fem or auxiliary genes--that, in addition to the mecA gene, are also critical for the expression of high-level and homogeneous resistance to methicillin. Genetic and/or biochemical analysis has shown that of the nearly dozen aux mutations described so far most are in genes involved in cell wall synthesis (murE, pbp2, glmM, glnR, femA/B, llm, etc.) or in complex regulatory functions (sigmaB), suggesting that optimal expression of resistance may involve the cooperative functioning of a number of genes in cell wall metabolism as well as stress response. The exact mechanism of these functions is not known. In an attempt to explore this unusual aspect of methicillin resistance more fully, a Tn551 transposon library, constructed in the background of the highly and homogeneously methicillin-resistant Staphylococcus aureus strain COL, was screened for all independent insertional mutants in which the level of methicillin resistance of the parental strain (MIC, 1,600 microg/ml) was reduced by at least 15-fold and up to 500-fold. We now describe the sequencing of 21 Tn551-inactivated genes and their vicinities in 23 new auxiliary mutants that have been studied before. Using the inverted polymerase chain reaction (IPCR), we amplified fragments corresponding to the right and left junction of the Tn551 insertions, which were then sequenced by primer walking. The two largest groups of these new auxiliary genes encoded either proteins of unknown functions (6 genes) or showed homology with genes encoding proteins involved with putative sensory/regulatory activities (7 genes: protein kinases, ABC transporters, and a catabolite control protein). Sequencing upstream and downstream allowed the identification of a number of additional open reading frames, some of which may also include functions relevant for the expression of antibiotic resistance.

Mrp--a new auxiliary gene essential for optimal expression of methicillin resistance in Staphylococcus aureus

Screening of a library of Tn551 insertional mutants selected for reduction in the methicillin resistance level of the parental Staphylococcus aureus strain COL resulted in the isolation of mutant RUSA266 in which the minimal inhibitory concentration (MIC) of the parent was reduced from 1,600 to 1.5 micrograms/mL. Cloning and sequencing of the vicinity of the insertion site omega 726 identified an open reading frame (orf1365) encoding a very large polypeptide of more than 1,365 amino acids. A unique feature of the deduced amino acid sequence was the presence of multiple tandem repeats of 75 amino acids in the polypeptide, reminiscent of the structure of high-molecular-weight cell-surface proteins EF* and Emb identified in some streptococcal strains. Mutant RUSA266 with the inactivated gene, which we shall provisionally refer to as mrp (for multiple repeat polypeptide), produced a peptidoglycan with altered muropeptide composition, and both the reduced antibiotic resistance and the altered cell wall composition were co-transduced in back-crosses into the parental strain COL. Additional sequencing upstream of mrp has revealed that this gene was part of a five-gene cluster occupying a 9.2-kb region of the staphylococcal chromosome and was composed of glmM (directly upstream of mrp), two open reading frames orf310 and orf269 coding for two hypothetical proteins, and the gene encoding the staphylococcal arginase (arg). Transcriptional analysis demonstrated that the five genes in the cluster were transcribed together.

Characterization and nucleotide sequence of a Klebsiella oxytoca cryptic plasmid encoding a CMY-type beta-lactamase: confirmation that the plasmid-mediated cephamycinase originated from the Citrobacter freundii AmpC beta-lactamase

Plasmid pTKH11, originally obtained by electroporation of a Klebsiella oxytoca plasmid preparation into Escherichia coli XAC, expressed a high level of an AmpC-like beta-lactamase. The enzyme, designated CMY-5, conferred resistance to extended-spectrum beta-lactams in E. coli; nevertheless, the phenotype was cryptic in the K. oxytoca donor. Determination of the complete nucleotide sequence of pTKH11 revealed that the 8,193-bp plasmid encoded seven open reading frames, including that for the CMY-5 beta-lactamase (blaCMY-5). The blaCMY-5 product was similar to the plasmidic CMY-2 beta-lactamase of K. pneumoniae and the chromosomal AmpC of Citrobacter freundii, with 99.7 and 97.0% identities, respectively; there was a substitution of phenylalanine in CMY-5 for isoleucine 105 in CMY-2. blaCMY-5 was followed by the Blc and SugE genes of C. freundii, and this cluster exhibited a genetic organization identical to that of the ampC region on the chromosome of C. freundii; these results confirmed that C. freundii AmpC was the evolutionary origin of the plasmidic cephamycinases. In the K. oxytoca host, the copy number of pTKH11 was very low and the plasmid coexisted with plasmid pNBL63. Analysis of the replication regions of the two plasmids revealed 97% sequence similarity in the RNA I transcripts; this result implied that the two plasmids might be incompatible. Incompatibility of the two plasmids might explain the cryptic phenotype of blaCMY-5 in K. oxytoca through an exclusion effect on pTKH11 by resident plasmid pNBL63.

Genetic characterization of resistance to extended-spectrum beta-lactams in Klebsiella oxytoca isolates recovered from patients with septicemia at hospitals in the Stockholm area

Two beta-lactamase gene regions were characterized by DNA sequencing in eight clinical isolates of Klebsiella oxytoca. The blaOXY-2a region encoded a beta-lactamase nearly identical to OXY-2 (one amino acid residue substituted) and conferred aztreonam and cefuroxime resistance on the K. oxytoca isolates. Overproduction of OXY-2a was caused by a G-to-A substitution of the fifth nucleotide in the -10 consensus sequence of blaOXY-2a. The blaOXY-1a was identified in a susceptible strain, and the OXY-1a enzyme differed from OXY-1 by two amino acid residues.

Secondary lymphoid-tissue chemokine (SLC) stimulates integrin alpha 4 beta 7-mediated adhesion of lymphocytes to mucosal addressin cell adhesion molecule-1 (MAdCAM-1) under flow

The attachment of leukocytes to the endothelium is a multistep process that depends upon a very rapid increase in the adhesive activity of leukocyte integrins. A pertussis toxin-sensitive pathway stimulates integrin-dependent lymphocyte adhesion to Peyer's patch high endothelial venules in vivo, but the factors responsible for activating this pathway have not been identified previously. We now report that secondary lymphoid-tissue chemokine (SLC) (also known as 6Ckine, Exodus-2, and thymus-derived chemotactic agent 4), a recently described CC chemokine that is expressed in Peyer's patches and lymph nodes, rapidly activates integrin-mediated lymphocyte adhesion. Immobilized SLC increased the adhesion of HUT-78 T cells and human PBLs to mucosal addressin cell adhesion molecule-1, a protein that is expressed on Peyer's patch and mesenteric lymph node high endothelial venules. This effect of SLC was seen in both static and flow chamber adhesion assays, was mediated by integrin alpha 4 beta 7, and was inhibited by pertussis toxin. The other CC chemokines tested did not increase adhesion to mucosal addressin cell adhesion molecule-1. SLC had a greater effect on naive CD4+ T cells than on memory CD4+ T cells; CD8+ T cells, B cells, and NK cells were also responsive to SLC. SLC is likely to play an important role in regulating the recruitment of lymphocytes to Peyer's patches and lymph nodes.

Additive vector decoding of transform coded images

In a standard transform coding scheme of images or video, the decoder can be implemented by a table-lookup technique without the explicit use of an inverse transformation, In this new decoding method, each received code index of a transform coefficient addresses a particular codebook to fetch a component code vector that resembles the basis vector of the linear transformation. The output image is then reconstructed by summing a small number of nonzero component code vectors. With a set of well-designed codebooks, this new decoder can exploit the correlation among the quantized transform coefficients to achieve better rate-distortion performance than the conventional decoding method. An iterative algorithm for designing a set of locally optimal codebooks from a training set of images is presented. We demonstrate that this new idea can be applied to decode improved quality pictures from the bitstream generated from a standard encoding scheme of still images or video, while the complexity is low enough to justify practical implementation.

Structure-function analysis of the integrin beta 7 subunit: identification of domains involved in adhesion to MAdCAM-1

Beta 7 integrins serve special roles in mucosal immunity. Alpha 4 beta 7-mediated adhesion to mucosal addressin cell adhesion molecule-1 (MAdCAM-1) directs lymphocyte homing to the gut, and alpha E beta 7 mediates binding of lymphocytes to E-cadherin on epithelial cells. Since alpha 4 beta 7 mediates adhesion to MAdCAM-1 but alpha 4 beta 1 does not, we used beta 7/beta 1 chimeras to directly assess the importance of specific regions of beta 7 in MAdCAM-1 binding. We found a region of beta 7 (residues 46-386) that accounts for specificity of alpha 4 beta 7 binding to MAdCAM-1. We also used human/mouse and human/rat chimeric beta 7 subunits to map epitopes recognized by fifteen anti-beta 7 mAbs. Six of seven Abs that block adhesion to MAdCAM-1 and E-cadherin (Fib 21, 22, 27, 30, 504; Act-1) mapped to amino acid residues 176-250. Residues 176-250 lie within the region of beta 7 that specifies MAdCAM-1 binding and also within a region that has a predicted structure homologous to the metal ion-dependent adhesion site (MIDAS) domains of the integrin subunits alpha L and alpha M. Three new Abs that recognize beta 7 in the presence of Mn2+, but not Ca2+, and promote adhesion to MAdCAM-1, mapped to amino acids 46-149. One blocking and five other Abs mapped to other regions (amino acids 387-725). We conclude that a MIDAS-like domain serves a critical role in beta 7 integrin-mediated adhesion.

Structure-function analysis of the integrin beta 7 subunit: identification of domains involved in adhesion to MAdCAM-1

Beta 7 integrins serve special roles in mucosal immunity. Alpha 4 beta 7-mediated adhesion to mucosal addressin cell adhesion molecule-1 (MAdCAM-1) directs lymphocyte homing to the gut, and alpha E beta 7 mediates binding of lymphocytes to E-cadherin on epithelial cells. Since alpha 4 beta 7 mediates adhesion to MAdCAM-1 but alpha 4 beta 1 does not, we used beta 7/beta 1 chimeras to directly assess the importance of specific regions of beta 7 in MAdCAM-1 binding. We found a region of beta 7 (residues 46-386) that accounts for specificity of alpha 4 beta 7 binding to MAdCAM-1. We also used human/mouse and human/rat chimeric beta 7 subunits to map epitopes recognized by fifteen anti-beta 7 mAbs. Six of seven Abs that block adhesion to MAdCAM-1 and E-cadherin (Fib 21, 22, 27, 30, 504; Act-1) mapped to amino acid residues 176-250. Residues 176-250 lie within the region of beta 7 that specifies MAdCAM-1 binding and also within a region that has a predicted structure homologous to the metal ion-dependent adhesion site (MIDAS) domains of the integrin subunits alpha L and alpha M. Three new Abs that recognize beta 7 in the presence of Mn2+, but not Ca2+, and promote adhesion to MAdCAM-1, mapped to amino acids 46-149. One blocking and five other Abs mapped to other regions (amino acids 387-725). We conclude that a MIDAS-like domain serves a critical role in beta 7 integrin-mediated adhesion.

Site-specific RNase E cleavage of oligonucleotides and inhibition by stem-loops

The enzyme RNase E (ref. 1) cuts RNA at specific sites within single-stranded segments. The role of adjacent regions of secondary structure in such cleavages is controversial. Here we report that 10-13-nucleotide oligomers lacking any stem-loop but containing the RNase E-cleaved sequence of RNA I, the antisense repressor of replication of ColE1-type plasmids, are cut at the same phosphodiester bond as, and 20 times more efficiently than, RNA I. These findings indicate that, contrary to previous proposals, stem-loops do not serve as entry sites for RNase E, but instead limit cleavage at potentially susceptible sites. Cleavage was reduced further by mutations in a non-adjacent stem-loop, suggesting that distant conformational changes can also affect enzyme access. Modulation of RNase E cleavages by stem-loop regions and to a lesser extent by higher-order structure may explain why this enzyme, which does not have stringent sequence specificity, cleaves complex RNAs at a limited number of sites.

Joint estimation of forward and backward motion vectors for interpolative prediction of video

A low-complexity iterative algorithm is introduced for joint estimation of forward and backward motion vectors in interpolative prediction of video. Starting from the initial values obtained by a commonly-used block matching independent search method, the motion vectors are iteratively refined until a locally optimal solution to the motion estimation problem for interpolative prediction is achieved. Each iteration consists of a series of two similar procedures. First, the backward motion vector is fixed and a new forward motion vector is searched to minimize the interpolation error. Then the forward motion vector is fixed and the backward motion vector is similarly refined by minimizing the interpolation error. This process is repeated until the interpolation error stops decreasing. Computer simulation results demonstrate that with this technique the prediction error in some scenes is significantly reduced.

Extended spectrum beta-lactamase from Klebsiella oxytoca, not belonging to the TEM or SHV family

In clinical isolates of Klebsiella oxytoca resistance to cefuroxime and aztreonam was mediated by a beta-lactamase, designated KH, (pI 5.25) which could be transferred into Escherichia coli by electroporation, but not by conjugation. The transformants produced two enzymes with pIs 5.25 and 8.4 respectively, and showed resistance to cefuroxime, aztreonam, cefotaxime and ceftazidime. Substrate and inhibition profiles indicated that KH beta-lactamase was different from TEM- or SHV-like enzymes, but similar to chromosomal K1 beta-lactamase. The enzyme profile with pI 8.4 was similar to the enzyme from the recipient and showed elevated activity in transformants. The plasmid profiles of the transformants were different from those of their donors. However, a plasmid fragment of the K. oxytoca isolate KH11 hybridized with a plasmid ranging in size from 4.8 to 7.8 kilobases in all the transformants and most of the donors. Gene probes encoding TEM-1 or SHV-1 did not hybridize with plasmid DNA from the K. oxytoca isolates. Furthermore, a probe of the ampC gene did not hybridize with the plasmid but to DNA fragments of the same size in whole cell DNA preparations from the E. coli XAC recipient and the TKH11 transformants. This indicates that no gross rearrangements in the chromosomal beta-lactamase gene region had occurred in the transformants which could explain the increased expression of the pI 8.4 beta-lactamase.