Negligible In Vitro Recovery of Macromolecules from Microdialysis Using 100 kDa Probes and Dextran in Perfusion Fluid

Microdialysis is applied in neurointensive care to monitor cerebral glucose metabolism. If recoverable, macromolecules may also serve as biomarkers in brain disease and provide clues to their passage across the blood-brain barrier. Our study aimed to investigate the in vitro recovery of human micro- and macromolecules using microdialysis catheters and perfusion fluids approved for clinical use. In vitro microdialysis of a bulk solution containing physiological or supraphysiological concentrations of glucose, lactate, pyruvate, human IgG, serum albumin, and hemoglobin was performed using two different catheters and perfusion fluids. One had a membrane cut-off of 20 kDa and was used with a standard CNS perfusion fluid, and the other had a membrane cut-off of 100 kDa and was perfused with the same solution supplemented with dextran. The flow rate was 0.3 µl/min. We used both push and push-pull methods. Dialysate samples were collected at 2-h intervals for 6 h and analyzed for relative recovery of each substance. The mean relative recovery of glucose, pyruvate, and lactate was > 90% in all but two sets of experiments. In contrast, the relative recovery of human IgG, serum albumin, and hemoglobin from both bulk solutions was below the lower limit of quantification (LLOQ). Using a push-pull method, recovery of human IgG, serum albumin, and hemoglobin from a bulk solution with supraphysiological concentrations were above LLOQ but with low relative recovery (range 0.9%-1.6%). In summary, exchanging the microdialysis setup from a 20 kDa catheter with a standard perfusion fluid for a 100 kDa catheter with a perfusion solution containing dextran did not affect the relative recovery of glucose and its metabolites. However, it did not result in any useful recovery of the investigated macromolecules at physiological levels, either with or without a push-pull pump system.

Stress-free blood sampling in minipigs: A novel method for assessing 24-h cortisol profiles and drug effects on diurnal and ultradian rhythms

We developed a novel, stress-free blood sampling method for minipigs, allowing continuous cortisol monitoring over 24 h. Baseline cortisol levels exhibited both ultradian and diurnal rhythms. During nighttime, smaller ultradian rhythms overlaid a lower baseline cortisol, which increased in sleeping pigs before lights were turned on. Additionally, we developed an analytical tool based on the R package "pracma" to quantify ultradian peak and circadian components of the cortisol profiles. To validate our model, we investigated the effects of Verucerfont, a CRH receptor antagonist, and Venlafaxine, a serotonin-norepinephrine reuptake inhibitor. Verucerfont reduced cortisol levels during the first 9 h without affecting diurnal rhythm. Cortisol peak parameters decreased, with a 31% reduction in overall area under the curve (AUC) and a 38% reduction in ultradian average AUC. Ultradian peaks decreased from 7 to 4.5, with 34% lower amplitude. Venlafaxine maintained plasma concentrations within the targeted human effective range. This method enables us to enhance our understanding of cortisol regulation and provide valuable insights for the impact of investigation drugs on the diurnal and ultradian rhythms of cortisol.

Investigating surrogate cerebrospinal fluid matrix compositions for use in quantitative LC-MS analysis of therapeutic antibodies in the cerebrospinal fluid

As quantitative analysis of biotherapeutics in cerebrospinal fluid (CSF) with LC-MS becomes increasingly widespread, there is a need for method developments towards higher sensitivity. By using artificial CSF (aCSF) in the development phase, the consumption of costly and sparsely available CSF can be limited. The aCSF compositions tested here were made from various dilutions of bovine serum albumin (BSA) or rat plasma to mimic the total protein concentration found in CSF. Focusing on monoclonal antibodies, the aCSF was spiked with human immunoglobulin (hIgG) and prepared with the bottom-up analysis technique using LC-MS. Assuming that the composition of the aCSF would affect the digest, the response from aCSF matrices was compared with CSF from rat, monkey, and dog in terms of estimated sample concentration and matrix effects. The samples were spiked with hIgG in the range of 10 to 1000 ng/mL and volumes of 10 μL were transferred to sample preparation. The results indicate that BSA dilutions from 300 to 2000 μg/mL and rat plasma dilutions of 0.5–2% provide the most accurate concentration estimates when compared with rat CSF. 1000 μg/mL BSA did not produce significantly different concentration estimates for 500 ng/mL samples when compared with CSF from rat, monkey, and dog, and can therefore be used as aCSF for several different species.

A comprehensive profile of recurrent glioblastoma

In spite of relentless efforts to devise new treatment strategies, primary glioblastomas invariably recur as aggressive, therapy-resistant relapses and patients rapidly succumb to these tumors. Many therapeutic agents are first tested in clinical trials involving recurrent glioblastomas. Remarkably, however, fundamental knowledge on the biology of recurrent glioblastoma is just slowly emerging. Here, we review current knowledge on recurrent glioblastoma and ask whether and how therapies change intra-tumor heterogeneity, molecular traits and growth pattern of glioblastoma, and to which extent this information can be exploited for therapeutic decision-making. We conclude that the ability to characterize and predict therapy-induced changes in recurrent glioblastoma will determine, whether, one day, glioblastoma can be contained in a state of chronic disease.

Characterization of midazolam metabolism in locusts: the role of a CYP3A4-like enzyme in the formation of 1'-OH and 4-OH midazolam

1. The metabolism of midazolam was investigated in vivo in locusts in order to evaluate the presence of an enzyme with functionality similar to human CYP3A4/5. 2. Hydroxylated metabolites of midazolam identical to human metabolites were detected in locusts and the apparent affinities (Km values) were in the same range as reported in humans (in locusts: 7-23 and 33-85 µM for the formation of the 1'-OH and 4-OH metabolites, respectively). 3. The formation of hydroxylated metabolites could successfully be inhibited by co-administration of ketoconazole, a known CYP3A4/5 inhibitor. 4. Besides phase I metabolites, a number of conjugated metabolites were detected using high-resolution mass spectrometry. The most abundant metabolites detected were structurally identified by (1)H NMR as two N-glucosides. NMR analysis strongly suggested that the glycosylation occurred at the two nitrogens (either one in each case) of the imidazole ring. 5. Distribution of midazolam and the glucose conjugates were successfully measured using desorption electrospray mass spectrometry imaging revealing time-dependent changes in distribution over time. 6. In conclusion, it appears that an enzyme with functionality similar to human CYP3A4/5 is present in locusts. However, it appears that conjugation with glucose is the main detoxification pathway of midazolam in locusts.

Depression and emotional stress is highly prevalent among women with recurrent pregnancy loss

STUDY QUESTION

Is the prevalence of psychological stress and moderate/severe depression higher for women with recurrent pregnancy loss (RPL) than pregnancy planners trying to conceive naturally?

SUMMARY ANSWER

Both psychological stress and major depression are significantly more common among women with RPL than in those trying to conceive naturally.

WHAT IS KNOWN ALREADY

RPL has a significant emotional impact on couples, especially the woman. Previous studies have shown inconclusive results.

STUDY DESIGN, SIZE, DURATION

In this cross-sectional study, we compared the prevalence of stress and depression among 301 women with RPL and 1813 women attempting to conceive naturally. We defined RPL as three or more pregnancy losses before 12 weeks' gestation. RPL patients were enrolled from 2010 to 2013 and the comparison group from 2011 to 2014.

PARTICIPANTS/MATERIALS, SETTING, METHODS

RPL patients completed an online questionnaire before their first consultation at the Danish RPL Unit. In addition, we included data from a comparison group of 1813 women who participated in the Soon Parents Study (www.SnartForældre.dk). The Major Depression Index (MDI) was used to assess symptoms of depression, and Cohen's Perceived Stress Scale (PSS) was used to measure stress. Relevant demographic data were also retrieved.

MAIN RESULTS AND THE ROLE OF CHANCE

Of the RPL patients, 26 (8.6%) had a score on the MDI corresponding to moderate/severe depression, as did 40 (2.2%) of the women in Soon Parents Study (adjusted odds ratio (OR) 5.53 (95% confidence interval (CI): 2.09; 14.61)). A high stress level, defined as ≥19 on the PSS scale, was reported by 124 (41.2%) of the patients and 420 (23.2%) in the comparison group (adjusted OR 1.59 (95% CI 1.03; 2.44)).

LIMITATIONS, REASONS FOR CAUTION

We used online questionnaires, and have no interview data. We were unaware if any of the women in the comparison group suffer from RPL.

WIDER IMPLICATIONS OF THE FINDINGS

This study should entail a heightened awareness of mental distress among care providers for women with RPL.

STUDY FUNDING/COMPETING INTERESTS

No specific funding was sought for this study. The Soon Parents Study is funded by National Institute of Child Health and Human Development (R01 HD060680-01A4). No authors have competing interests to declare.

TRIAL REGISTRATION NUMBER

N/A.

Characterization of a novel brain barrier ex vivo insect-based P-glycoprotein screening model

In earlier studies insects were proposed as suitable models for vertebrate blood–brain barrier (BBB) permeability prediction and useful in early drug discovery. Here we provide transcriptome and functional data demonstrating the presence of a P-glycoprotein (Pgp) efflux transporter in the brain barrier of the desert locust (Schistocerca gregaria). In an in vivo study on the locust, we found an increased uptake of the two well-known Pgp substrates, rhodamine 123 and loperamide after co-administration with the Pgp inhibitors cyclosporine A or verapamil. Furthermore, ex vivo studies on isolated locust brains demonstrated differences in permeation of high and low permeability compounds. The vertebrate Pgp inhibitor verapamil did not affect the uptake of passively diffusing compounds but significantly increased the brain uptake of Pgp substrates in the ex vivo model. In addition, studies at 2°C and 30°C showed differences in brain uptake between Pgp-effluxed and passively diffusing compounds. The transcriptome data show a high degree of sequence identity of the locust Pgp transporter protein sequences to the human Pgp sequence (37%), as well as the presence of conserved domains. As in vertebrates, the locust brain–barrier function is morphologically confined to one specific cell layer and by using a whole-brain ex vivo drug exposure technique our locust model may retain the major cues that maintain and modulate the physiological function of the brain barrier. We show that the locust model has the potential to act as a robust and convenient model for assessing BBB permeability in early drug discovery.

The grasshopper: a novel model for assessing vertebrate brain uptake

The aim of the present study was to develop a blood-brain barrier (BBB) permeability model that is applicable in the drug discovery phase. The BBB ensures proper neural function, but it restricts many drugs from entering the brain, and this complicates the development of new drugs against central nervous system diseases. Many in vitro models have been developed to predict BBB permeability, but the permeability characteristics of the human BBB are notoriously complex and hard to predict. Consequently, one single suitable BBB permeability screening model, which is generally applicable in the early drug discovery phase, does not yet exist. A new refined ex vivo insect-based BBB screening model that uses an intact, viable whole brain under controlled in vitro-like exposure conditions is presented. This model uses intact brains from desert locusts, which are placed in a well containing the compound solubilized in an insect buffer. After a limited time, the brain is removed and the compound concentration in the brain is measured by conventional liquid chromatography-mass spectrometry. The data presented here include 25 known drugs, and the data show that the ex vivo insect model can be used to measure the brain uptake over the hemolymph-brain barrier of drugs and that the brain uptake shows linear correlation with in situ perfusion data obtained in vertebrates. Moreover, this study shows that the insect ex vivo model is able to identify P-glycoprotein (Pgp) substrates, and the model allows differentiation between low-permeability compounds and compounds that are Pgp substrates.

Hip fractures in a city in Northern Norway over 15 years: time trends, seasonal variation and mortality : the Harstad Injury Prevention Study

In this open population-based study from Northern Norway, there was no increase in hip fracture incidence in women and men from 1994 to 2008. Age-adjusted hip fracture rates was lower compared to reported rates from the Norwegian capital Oslo, indicating regional differences within the country.

INTRODUCTION

The aim of the present population-based study was to describe age- and sex-specific incidence of hip fractures in a Northern Norwegian city, compare rates with the Norwegian capital Oslo, describe time trends in hip fracture incidence, place of injury, seasonal variation and compare mortality after hip fracture between women and men.

METHODS

Data on hip fractures from 1994 to 2008 in women and men aged 50 years and above were obtained from the Harstad Injury Registry.

RESULTS

There were altogether 603 hip fractures in Harstad between 1994 and 2008. The annual incidenc rose exponentially from 5.8 to 349.2 per 10,000 in men, and from 8.7 to 582.2 per 10,000 in women from the age group 50-54 to 90+ years. The age-adjusted incidence rates were 101.0 and 37.4 in women and men, respectively, compared to 118.0 in women (p = 0.005) and 44.0 in men (p = 0.09) in Oslo. The age-adjusted incidence rates did not increase between 1994-1996 and 2006-2008. The majority of hip fractures occurred indoors and seasonal variation was significant in fractures occurring outdoors only. After adjusting for age at hip fracture, mortality after fracture was higher in men than in women 3, 6 and 12 months (p ≤ 0.002) after fracture.

CONCLUSIONS

There are regional differences in hip fracture incidence that cannot be explained by a north-south gradient in Norway. Preventive strategies must be targeted to indoor areas throughout the year and to outdoor areas in winter.

Mental distress in the Danish general population

OBJECTIVE

To present data on mental distress in the Danish general population using recently validated Hopkins symptom checklist (SCL) subscales and compare with data from other countries. To evaluate associations between mental distress and biopsychosocial factors.

METHOD

Questionnaires were sent to a gender- and age-stratified random sample comprising 2040 Danes. Mean SCL subscale scores were calculated. Cases were defined in accordance with the traditional criteria, and Danish and US raw score cut-offs were compared. A multiple regression model was developed to describe associations between biopsychosocial factors and SCL scores.

RESULTS

The response rate was 58%. The Danish mean scores were significantly higher than reported for a US non-patient sample, and Danish raw score cut-offs for caseness were higher. The Danish scores were closer to Nordic mean scores. Age, gender, social status, somatic disorder and traumatic life events in the past year in work life as well as personal life were significantly associated with the level of mental distress. SCL scores were compared with scores on the Major Depression Inventory.

CONCLUSION

The SCL mean scores of the Danish general population were relatively high, but similar to data from the Nordic countries. Consequently, interpretation of the Danish SCL requires Danish norms and Danish cut-off scores for caseness.

Modafinil augmentation in depressed patients with partial response to antidepressants: a pilot study on self-reported symptoms covered by the Major Depression Inventory (MDI) and the Symptom Checklist (SCL-92)

Treatment-resistant depression, i.e. partial or non response to antidepressants in spite of various treatment attempts with optimized doses and combinations, is rather common. With residual symptoms such as tiredness, anhedonia and concentration disturbances, the treatment strategy has often been to use monoamino-oxidase inhibitors (MAOIs). Their use, however, is limited due to interaction problems. Modafinil is recently developed wake-promoting drug with only minor side-effects. Pilot studies indicate that it appears to have an augmentation effect in treatment-resistant depression. This open-label study performed in the private psychiatric practice setting is the first to make a comprehensive evaluation of the target patient profile based on patient-reported symptoms. Modafinil in doses of 100-400 mg was administered as augmentation to ongoing antidepressant therapy in patients with partial response and suffering from hypersomnia. The total number of patients was 21 and 43% of these were responders (i.e. had a score reduction of >50% on the Major Depression Inventory (MDI) as well as remitters, i.e. the remission rate was 43%. At endpoint, the responders had psychological distress scores on the Symptom Checklist (SCL-92) on the level of the general Danish population. Baseline characteristics for responders were lower scores on depression, hostility, anxiety, somatization, obsession and psychoticism. Modafinil thus appears to be an appropriate augmentation to antidepressant treatment, leading to a remission rate of 43%. However, the results from this open-label study need ot be confirmed in a placebo-controlled trial.

The SCL-90 and SCL-90R versions validated by item response models in a Danish community sample

OBJECTIVE

To evaluate the internal validity of the subscales of the combined SCL-90 and SCL-90R, the SCL-92, by item response analyses as compared with several previously reported factor analyses of this questionnaire in the literature.

METHOD

The SCL-92 questionnaire was mailed to an age- and gender-stratified random sample of Danish citizens. The sample comprised 2040 individuals. The internal structure of the nine factors of the SCL-92 questionnaire was evaluated by Mokken-Loevinger analysis and Rasch analysis.

RESULTS

In total, 1153 persons or 58% returned the questionnaire fully completed. Mokken analysis found all scales apart from the psychoticism scale acceptable. The Rasch analysis found most of the subscales to be robust. Minor problems were seen for the scales of phobic anxiety, obsession-compulsion and depression. Analysis of the Global Severity Index showed that the Rasch model was rejected for the full 92-item scale, but not for a scale consisting of the 63 items from the non-psychotic subscales. Spearman correlations among the subscales were all positive (range 0.34-0.79) and so were correlations between each of the subscales and the Global Severity Index (range 0.55-0.91).

CONCLUSION

In this sample from the Danish general population the non-psychotic subscales, i.e. the subscales covering psychological distress were observed to function well. In a general population sample, the 63 non-psychotic items primarily appear to reflect one broad dimension of distress.

Prevalence of major depression and stress indicators in the Danish general population

OBJECTIVE

To estimate the prevalence rate of major depression in the Danish general population by using the Major Depression Inventory (MDI), a validated self-rating scale fulfilling the symptomatic criteria in DSM-IV and ICD-10 for a depressive episode.

METHOD

A booklet containing the MDI and a number of questions on psychosocial factors was sent to 2040 randomly selected Danish citizens. The sample was age- and gender-stratified. Mean MDI scores were calculated. Logistic regression analysis was used in order to produce a model for the influence of psychosocial factors.

RESULTS

The response rate was 60%. The point prevalence of major depression was 3.3%. Among the tested predictors of depression were sociodemographic variables, alcohol and smoking habit, bodily pain, somatic diseases and traumatic life events. For a traumatic event in personal life over the past year odds ratio was 6.4 [2.7; 15.5], for overconsumption of alcohol odds ratio was 3.2 [1.5; 6.8]. While the gender difference in major depression rate was not found statistically significant, a significant (P < 0.05) gender difference of male to female of 1 : 2 was found when including minor depression. Of people identified as having a major depression only 13% were currently treated by a medical doctor.

CONCLUSION

Major depression has a high prevalence in the Danish general population and seems to be undertreated. The gender difference was only found statistically significant when including minor depression, indicating that the female predominance is less pronounced in the more severe depression states.

The internal and external validity of the Major Depression Inventory in measuring severity of depressive states

BACKGROUND

We have developed the Major Depression Inventory (MDI), consisting of 10 items, covering the DSM-IV as well as the ICD-10 symptoms of depressive illness. We aimed to evaluate this as a scale measuring severity of depressive states with reference to both internal and external validity.

METHOD

Patients representing the score range from no depression to marked depression on the Hamilton Depression Scale (HAM-D) completed the MDI. Both classical and modern psychometric methods were applied for the evaluation of validity, including the Rasch analysis.

RESULTS

In total, 91 patients were included. The results showed that the MDI had an adequate internal validity in being a unidimensional scale (the total score an appropriate or sufficient statistic). The external validity of the MDI was also confirmed as the total score of the MDI correlated significantly with the HAM-D (Pearson's coefficient 0.86, P < or = 0.01, Spearman 0.80, P < or = 0.01).

CONCLUSION

When used in a sample of patients with different states of depression the MDI has an adequate internal and external validity.

The sensitivity and specificity of the Major Depression Inventory, using the Present State Examination as the index of diagnostic validity

BACKGROUND

A self-rating inventory has been developed to measure DSM-IV and ICD-10 diagnoses of major (moderate to severe) depression by the patients' self-reported symptoms. This Major Depression Inventory (MDI) can be scored both according to the DSM-IV and the ICD-10 algorithms for depressive symptomatology and according to severity scales by the simple total sum of the items.

METHODS

The Schedule for Clinical Assessment in Neuropsychiatry (SCAN) was used as index of validity for the clinician's DSM-IV and ICD-10 diagnosis of major (moderate to severe) depression. The sensitivity and specificity of MDI was assessed in a sample of 43 subjects covering a spectrum of depressive symptoms.

RESULTS

The sensitivity of the MDI algorithms for major depression varied between 0.86 and 0.92. The specificity varied between 0.82 and 0.86. When using the total score of MDI the optimal cut-off score was estimated 26 and the total score was shown to be a sufficient statistic.

LIMITATIONS

The sample of subjects was limited. Patients with psychotic depression were not included.

CONCLUSION

The MDI was found to have a sensitivity and specificity which is acceptable. The questionnaire is brief and can be scored diagnostically by the DSM-IV and ICD-10 algorithms as well as by its simple total score.

Structure of the Escherichia coli GlmU pyrophosphorylase and acetyltransferase active sites

N-Acetylglucosamine-1-PO(4) uridyltransferase (GlmU) is a trimeric bifunctional enzyme that catalyzes the last two sequential reactions in the de novo biosynthetic pathway for UDP-GlcNAc. The X-ray crystal structure of Escherichia coli GlmU in complex with UDP-GlcNAc and CoA has been determined to 2.1 A resolution and reveals a two-domain architecture that is responsible for these two reactions. The C-terminal domain is responsible for the CoA-dependent acetylation of Glc-1-PO(4) to GlcNAc-1-PO(4) and displays the longest left-handed parallel beta-helix observed to date. The acetyltransferase active site defined by the binding site for CoA makes use of residues from all three subunits and is positioned beneath an open cavity large enough to accommodate the Glc-1-PO(4) acetyl acceptor. The N-terminal domain catalyzes uridyl transfer from UTP to GlcNAc-1-PO(4) to form the final products UDP-GlcNAc and pyrophosphate. This domain is composed of a central seven-stranded beta-sheet surrounded by six alpha-helices in a Rossmann fold-like topology. A Co(2+) ion binds to just one of the two independent pyrophosphorylase active sites present in the crystals studied here, each of which nonetheless binds UDP-GlcNAc. The conformational changes of the enzyme and sugar nucleotide that accompany metal binding may provide a window into the structural dynamics that accompany catalysis.

[Logbook. A possible method]

The European board of psychiatry recommends the use of a logbook and checklist. There has been discussion about the extent of registration--and the resources involved. We present a simple method of registering supervision. Trainees make a daily report of the amount of supervision received. The trial period was divided into two sections: March, April and May 1997; (training intensive) and June, July and August 1997; (holiday season). The trainees responded well to the logbook, the answering rate was 94.2% in the first period, 60.9% in the holiday season. Calculations based on the first period show that trainees receive supervision during 9.8% of their working hours (range 4.8-16.0). Twenty-nine percent of supervision is of the direct variety, where both trainer and trainee are present. This variety suffers during holiday season. This type of logbook provides an opportunity to be directed in training activities, with a minimum of resources involved.

Insertions into the beta3-beta4 hairpin loop of HIV-1 reverse transcriptase reveal a role for fingers subdomain in processive polymerization

Human immunodeficiency virus type 1 (HIV-1) reverse transcriptase (RT) displays a characteristic poor processivity during DNA polymerization. Structural elements of RT that determine processivity are poorly understood. The three-dimensional structure of HIV-1 RT, which assumes a hand-like structure, shows that the fingers, palm, and thumb subdomains form the template-binding cleft and may be involved in determining the degree of processivity. To assess the influence of fingers subdomain of HIV-1 RT in polymerase processivity, two insertions were engineered in the beta3-beta4 hairpin of HIV-1NL4-3 RT. The recombinant mutant RTs, named FE20 and FE103, displayed wild type or near wild type levels of RNA-dependent DNA polymerase activity on all templates tested and wild type or near wild type-like sensitivities to dideoxy-NTPs. When polymerase activities were measured under conditions that allow a single cycle of DNA polymerization, both of the mutants displayed 25-30% greater processivity than wild type enzyme. Homology modeling the three-dimensional structures of wild type HIV-1NL4-3 RT and its finger insertion mutants revealed that the extended loop between the beta3 and beta4 strands protrudes into the cleft, reducing the distance between the fingers and thumb subdomains to approximately 12 A. Analysis of the models for the mutants suggests an extensive interaction between the protein and template-primer, which may reduce the degree of superstructure in the template-primer. Our data suggest that the beta3-beta4 hairpin of fingers subdomain is an important determinant of processive polymerization by HIV-1 RT.

X-ray crystallographic studies of unique cross-linked lattices between four isomeric biantennary oligosaccharides and soybean agglutinin

Soybean agglutinin (SBA) (Glycine max) is a tetrameric GalNAc/Gal-specific lectin which forms unique cross-linked complexes with a series of naturally occurring and synthetic multiantennary carbohydrates with terminal GalNAc or Gal residues [Gupta et al. (1994) Biochemistry 33, 7495-7504]. We recently reported the X-ray crystal structure of SBA cross-linked with a biantennary analog of the blood group I carbohydrate antigen [Dessen et al. (1995) Biochemistry 34, 4933-4942]. In order to determine the molecular basis of different carbohydrate-lectin cross-linked lattices, a comparison has been made of the X-ray crystallographic structures of SBA cross-linked with four isomeric analogs of the biantennary blood group I carbohydrate antigen. The four pentasaccharides possess the common structure of (beta-LacNAc)2Gal-beta-R, where R is -O(CH2)5COOCH3. The beta-LacNAc moieties in the four carbohydrates are linked to the 2,3-, 2,4-, 3,6-, and 2,6-positions of the core Gal residue(s), respectively. The structures of all four complexes have been refined to approximately 2.4-2.8 A. Noncovalent lattice formation in all four complexes is promoted uniquely by the bridging action of the two arms of each bivalent carbohydrate. Association between SBA tetramers involves binding of the terminal Gal residues of the pentasaccharides at identical sites in each monomer, with the sugar(s) cross-linking to a symmetry-related neighbor molecule. While the 2,4-, 3,6-, and 2,6-pentasaccharide complexes possess a common P6422 space group, their unit cell dimensions differ. The 2, 3-pentasaccharide cross-linked complex, on the other hand, possesses the space group I4122. Thus, all four complexes are crystallographically distinct. The four cross-linking carbohydrates are in similar conformations, possessing a pseudo-2-fold axis of symmetry which lies on a crystallographic 2-fold axis of symmetry in each lattice. In the case of the 3,6- and 2,6-pentasaccharides, the symmetry of their cross-linked lattices requires different rotamer orientations about their beta(1,6) glycosidic bonds. The results demonstrate that crystal packing interactions are the molecular basis for the formation of distinct cross-linked lattices between SBA and four isomeric pentasaccharides. The present findings are discussed in terms of lectins forming unique cross-linked complexes with glycoconjugate receptors in biological systems.

X-ray crystallographic studies of unique cross-linked lattices between four isomeric biantennary oligosaccharides and soybean agglutinin

Soybean agglutinin (SBA) (Glycine max) is a tetrameric GalNAc/Gal-specific lectin which forms unique cross-linked complexes with a series of naturally occurring and synthetic multiantennary carbohydrates with terminal GalNAc or Gal residues [Gupta et al. (1994) Biochemistry 33, 7495-7504]. We recently reported the X-ray crystal structure of SBA cross-linked with a biantennary analog of the blood group I carbohydrate antigen [Dessen et al. (1995) Biochemistry 34, 4933-4942]. In order to determine the molecular basis of different carbohydrate-lectin cross-linked lattices, a comparison has been made of the X-ray crystallographic structures of SBA cross-linked with four isomeric analogs of the biantennary blood group I carbohydrate antigen. The four pentasaccharides possess the common structure of (beta-LacNAc)2Gal-beta-R, where R is -O(CH2)5COOCH3. The beta-LacNAc moieties in the four carbohydrates are linked to the 2,3-, 2,4-, 3,6-, and 2,6-positions of the core Gal residue(s), respectively. The structures of all four complexes have been refined to approximately 2.4-2.8 A. Noncovalent lattice formation in all four complexes is promoted uniquely by the bridging action of the two arms of each bivalent carbohydrate. Association between SBA tetramers involves binding of the terminal Gal residues of the pentasaccharides at identical sites in each monomer, with the sugar(s) cross-linking to a symmetry-related neighbor molecule. While the 2,4-, 3,6-, and 2,6-pentasaccharide complexes possess a common P6422 space group, their unit cell dimensions differ. The 2, 3-pentasaccharide cross-linked complex, on the other hand, possesses the space group I4122. Thus, all four complexes are crystallographically distinct. The four cross-linking carbohydrates are in similar conformations, possessing a pseudo-2-fold axis of symmetry which lies on a crystallographic 2-fold axis of symmetry in each lattice. In the case of the 3,6- and 2,6-pentasaccharides, the symmetry of their cross-linked lattices requires different rotamer orientations about their beta(1,6) glycosidic bonds. The results demonstrate that crystal packing interactions are the molecular basis for the formation of distinct cross-linked lattices between SBA and four isomeric pentasaccharides. The present findings are discussed in terms of lectins forming unique cross-linked complexes with glycoconjugate receptors in biological systems.

The nucleoside analog-resistant E89G mutant of human immunodeficiency virus type 1 reverse transcriptase displays a broader cross-resistance that extends to nonnucleoside inhibitors

The alteration of a glutamic acid (E) to a glycine (G) amino acid residue at position 89 (E89G alteration) in the human immunodeficiency virus type 1 reverse transcriptase confers decreased susceptibility to several nucleoside analog inhibitors. Because the nonnucleoside inhibitor-binding pocket is adjacent to the deoxynucleoside triphosphate substrate-binding site, the impact of the E89G reverse transcriptase has decreased susceptibility to TIBO R82150, nevirapine, and to a lesser extent, delavirdine. Human immunodeficiency viruses bearing the same mutation displayed decreased susceptibility to inhibition by these compounds in a cell culture virus replication assay.

Circular dichroism and Fourier transform infrared spectroscopic studies on the secondary structure of Saccharomyces cerevisiae and Escherichia coli phospho enolpyruvate carboxykinases

The secondary structure of Saccharomyces cerevisiae and Escherichia coli phospho enolpyruvate (PEP) carboxykinases was quantitatively examined using circular dichroism (CD) and Fourier transform infrared (FTIR) spectroscopies. From CD analyses, values of 24% alpha-helix and 38% beta-sheet were obtained for the E. coli enzyme, while the corresponding values for the S. cerevisiae PEP carboxykinase were 20% and 36%. Analysis of the amide I' infrared band indicated 20% alpha-helix and 36% beta-sheet for the S. cerevisiae enzyme, while for the E. coli protein values of 40% beta-sheet and between 9 and 36% alpha-helix could be inferred. It is concluded that the bacterial enzyme has more secondary structure elements than the yeast protein. No alteration of the CD or FTIR spectra was detected upon substrate or metal ion binding to any enzyme.

The structure of the MnIIADP-nitrate-lyxose complex at the active site of hexokinase

The coordination scheme of Mn2+ in the hexokinase-MnIIADP-nitrate-lyxose complex has been determined by electron paramagnetic resonance (EPR) spectroscopy with 17O-enriched ligands. Nitrate binds to the active site of hexokinase when MnIIADP and a sugar substrate or analogue are present. The binding of nitrate enhances inhibition by glucose when ADP is present and narrows the EPR signals of the enzyme-bound MnIIADP complex in the presence of sugar substrates or analogues. Experiments using regiospecifically 17O-enriched ADP, 17O-enriched nitrate, and 17O-enriched water establish the coordination scheme of Mn2+. The EPR experiments show that ADP is a beta-monodentate ligand and that nitrate binds directly to Mn2+. Four water molecules complete the coordination sphere of the enzyme-bound Mn2+. The dissociation constant (Kd approximately 8 mM) of nitrate for the complex with enzyme, MnIIADP, and lyxose was obtained from titration experiments. These results suggest that nitrate-stabilized, dead-end complexes of hexokinase may be useful in stabilizing the closed conformation of this "hinge-bending" enzyme for crystallographic experiments.