Bis-arylidene oxindoles for colorectal cancer nanotherapy

Oxindoles are potent anti-cancer agents and are also used against microbial and fungal infections and for treating neurodegenerative diseases. These oxindoles are earlier established as estrogen receptor (ER)-targeted agents for killing ER (+) cancer cells. Our previously developed bis-arylidene oxindole, Oxifen (OXF) exhibits effective targeting towards ER (+) cancer cells which has a structural resemblance with tamoxifen. Herein, we have designed and synthesized few structural analogues of OXF such as BPYOX, ACPOX and ACPOXF to examine its cytotoxicity in different cancer as well as non-cancer cell lines and its potential to form self- aggregates in aqueous solution. Among these series of molecules, ACPOXF showed maximum toxicity in colorectal cancer cell line which are ER (-) but it also kills non-cancer cell line HEK-293, thereby reducing its cancer cell selectivity. Incidentally, ACPOXF exhibits self-aggregation, without the help of a co-lipid with nanometric size in aqueous solution. ACPOXF self-aggregate was co-formulated with glucocorticoid receptor (GR) synthetic ligand, dexamethasone (Dex) (called, ACPOXF-Dex aggregate) which could selectively kill ER (-) colorectal cancer cells and also could increase survivability of colon-tumour bearing mice. ACPOXF-Dex induced ROS up-regulation followed by apoptosis through expression of caspase-3. Further, we observed upregulation of antiproliferative factor, p53 and epithelial-to-mesenchymal (EMT) reversal marker E-cadherin in tumour mass. In conclusion, a typical structural modification in ER-targeting Oxifen moiety resulted in its self-aggregation that enabled it to carry a GR-ligand, thus broadening its selective antitumor property especially as colon cancer therapeutics.

Glucocorticoid receptor mediated sensitization of colon cancer to photodynamic therapy induced cell death

Photodynamic therapy (PDT) is a clinically approved, non-invasive alternate cancer therapy. A synthetic glucocorticoid (GC), dexamethasone (Dex) has previously been demonstrated to sensitize cancer cells to chemotherapy. However, to the best of our knowledge, the sensitization effect of GCs on PDT has not yet been investigated. We hypothesized that glucocorticoid receptor (GR) targeting can selectively make cancer cells more sensitive to PDT treatment, as PDT induces hypoxia wherein GR-activity gets enhanced. In addition, Dex was reported to act against the PDT-induced cell survival pathways like HIF-1α, NRF2, NF-κB, STAT3 etc. Thus, both the treatments can complement each other and may result in increasing the effectiveness of combination therapy. Hence, in this study, we developed liposomal formulations of our previously reported PDT agent P-Nap, either alone (D1P-Nap) or in combination with Dex (D1XP-Nap) to elucidate the sensitization effect. Interestingly, our RT-PCR results in hypoxic conditions showed down-regulation of HIF-1α and over expression of GR-activated genes for glucose-6-phosphatase (G6Pase) and PEPCK enzymes, indicating prominent GR-transactivation. We also observed higher phototoxicity in CT26.WT cells treated with D1XP-Nap PDT under hypoxic conditions as compared to normoxic conditions. These effects were reversed when cells were pre-treated with RU486, a competitive inhibitor of GCs. Moreover, our in vivo findings of subcutaneous tumor model of Balb/C mice for colon cancer revealed a significant decrease in tumor volume as well as considerable enhancement in the survivability of PDT treated tumor-bearing mice when Dex was present in the formulation. A high Bax/Bcl-xL ratio, high p53 expression, enhanced E-cadherin expression and down-regulation of pro-tumorigenic transcription factors NF-κB and c-Myc were found in tumor lysates from mice treated with D1XP-Nap under PDT, indicating GR-mediated sensitization of the tumor to PDT-induced cell death and enhancement of life-span for tumor bearing mice.

Glucocorticoid receptor-targeted liposomal delivery system for delivering small molecule ESC8 and anti-miR-Hsp90 gene construct to combat colon cancer

High mortality rate in colon cancer patients is often attributed to late diagnosis. To overcome the conventional chemotherapy associated challenges, chemotherapeutic drugs (single or combination) or genetic drugs are often delivered using ligand-modified delivery systems that selectively target over expressed receptors or particular receptors that act abnormally in cancer cells. In the current investigation, first we assessed anti-colon cancer effect of a cationic estrogenic molecule, ESC8 which was earlier shown to act against estrogen receptor (ER) ± breast cancer cells. We found that against both colon and breast cancer cells the anticancer activity is intervened by AMPK-mTOR pathway and at the same time it acts as anti-angiogenic agent. It also showed enhancement of mesenchymal-to-epithelial (MET) transition as well as reduction of cyclin D in both cells. Earlier we demonstrated the use of glucocorticoid receptor (GR) targeted cationic liposomal delivery system carrying anti-Hsp90 plasmid and ESC8 to act as potent anti-skin cancer therapeutics. As ESC8 demonstrated anti-colon cancer effect in vitro, in here, we used the same GR-targeted liposomal formulation but carrying a more fusogenic cationic lipid D1 and used against colon tumor orthotopic model in mice. We show that GR targeted formulation (D1XE-Hsp90) exhibited efficient cellular uptake, transfection and selective cytotoxicity in colon cancer cells, tumor-targeted bio-distribution and enhanced survivability, reduced tumor size in orthotopic colon tumor-bearing mice. The tumor sections exhibited reduced tumor proliferation as well as neo-vascularization, thus supporting the holistic antitumor effect of the D1XE-Hsp90 formulation. Over all our results establish the GR-targeted D1XE-Hsp90 formulation as potent anti-colon cancer therapeutics.

Normal and Delayed Fracture Healing: Symphony and Cacophony

The incidence of any fracture in the US is estimated to be 2 704 fractures per 100,000 person-years. Approximately 10 percent of these fractures develop complications of healing. The processes that occur during fracture healing mimic the processes that take place in the growth plate during development. The study of fracture healing represents a window to enhance our understanding of the processes of growth and development of bones and its reparative biology. This review is aimed for clinicians evaluating non-unions as an overview of different factors that inhibit fracture healing.

Efficacy of radical radiotherapy alone for functional preservation of larynx in laryngeal carcinoma: a retrospective analysis

PURPOSE

Concurrent chemoradiation is the current standard of care in locally advanced head and neck cancer. But, in our setup, many patients of carcinoma larynx are treated with only radical radiotherapy because of poor general condition of the patients. This study was performed to assess the influence radical radiotherapy alone on functional preservation of larynx.

MATERIALS AND METHODS

110 previously untreated patients with invasive squamous cell carcinoma of larynx were treated with radical radiotherapy alone between January 2006 and June 2009. Conventional one daily fraction of 2 Gy with total doses of 60-66 Gy was used. Voice preservation and local control at median follow-up period of 2 years were analyzed. Several host, tumor, and treatment parameters were also analyzed.

RESULTS

Among 110 patients, preservation of larynx was possible in 78 patients (71%). With radical radiotherapy alone, excellent preservation of larynx was achieved in stage I (88.9%) and stage II (75%) disease, while in advanced stages, results were not so encouraging. In stage III and stage IVA, larynx preservation was only 72.4% and 65.3%, respectively. Patients without any cartilage invasion had significantly better laryngeal preservation rate as compared to patients with cartilage invasion. (78.9% vs. 35.3%; P = 0.008).

CONCLUSION

Though concurrent chemoradiation is the standard of care in preservation of voice in laryngeal cancer, definitive radiotherapy alone may also be a good option in terms of preservation of larynx in patients of laryngeal cancer in community practice in the developing world where most of the patients cannot tolerate concurrent chemoradiation.

Competing risk: An illustration with aspiration pneumonia in head and neck cancer patients undergoing radical radiotherapy: A biostatistician's perspective

Interest in survival analysis is to look and capture the information about the occurrence of events, i.e., death. In human life different types of events may happen at the same time. Sometimes, few events completely interrupt or make subtle changes on the occurrence of an event of interest. The method to capture information about the specific event of interest along with other events is known as competing risk modeling. This paper is dedicated to explore the application of competing risk model in oncology practice. It is aimed in near future that more and more survival analysis will be performed through application of competing risk modeling instead of traditional survival analysis to generate robust statistical inference.

Adherence to oral bisphosphonates and the risk of subtrochanteric and femoral shaft fractures among female medicare beneficiaries

Previous studies have shown an association between duration of bisphosphonate use and atypical femur fractures. This cohort study showed an increasingly higher risk of subtrochanteric and femoral shaft fractures among those who were more adherent to oral bisphosphonates.

INTRODUCTION

Long-term use of oral bisphosphonates has been implicated in an increased risk of atypical femur fractures located in subtrochanteric and femoral shaft regions. Another measure of drug exposure, medication adherence, however, has not been investigated.

METHODS

Among all Medicare fee-for-service female beneficiaries from 2006-2010, we followed 522,287 new bisphosphonate users from their index prescription until being censored or having a primary diagnosis of closed subtrochanteric/femoral shaft or intertrochanteric/femoral neck fractures. Data about radiographs of fracture site and features were not available. Adherence was classified according to the medication possession ratio (MPR) as the following: MPR < 1/3 as less compliant, MPR ≥ 1/3- < 2/3 as compliant, and MPR ≥ 2/3 as highly compliant. Alternative cutoff points at 50 and 80% were also used. Survival analysis was used to determine the cumulative incidence and hazard of subtrochanteric/femoral shaft or intertrochanteric/femoral neck fractures.

RESULTS

There was a graded increase in incidence of subtrochanteric/femoral shaft fractures as the level of adherence increased (Gray's test, P < 0.001). The adjusted hazard ratio (HR) for the highly compliant vs. the less compliant was 1.23 (95% Confidence Interval [CI] 1.06-1.43) overall, became significant after 2 years of follow-up (HR = 1.51, 95% CI 1.06-2.15) and reached the highest risk in the fifth year (HR = 4.06, 95% CI 1.47-11.19). However, age-adjusted incidence rates of intertrochanteric/femoral neck fractures were significantly lower among highly compliant beneficiaries, compared to less compliant users (HR = 0.69, 95% CI 0.66-0.73). Similar results were obtained when the cutoff points for being compliant and highly compliant were set at 50 and 80 %, respectively.

CONCLUSIONS

Subtrochanteric/femoral shaft fractures, unlike intertrochanteric/femoral neck fractures, are positively associated with higher adherence to long-term (≥3 years) oral bisphosphonates in the elderly female Medicare population.

Possible approach for serodiagnosis of ascariasis by evaluation of immunoglobulin G4 response using Ascaris lumbricoides somatic antigen

Somatic antigen of Ascaris lumbricoides was purified to homogeneity (molecular mass, 34 kDa) by ammonium sulfate fractionation and successive chromatographic procedures, namely, gel permeation, ion exchange, and high-performance gel permeation liquid chromatographies. The antigen showed strong binding with immunoglobulin G (IgG) in Ascaris-infested patients and was cross-reactive with IgE and IgG in patients infested with other nematodes. It reacted specifically with IgG4 (P < 0.001) in 63 Ascaris-infested patients, which represented 65% of the total IgG response, though cross-reactivity with IgG1, IgG2, and IgG3 subclasses was observed, indicating the unique specificity of this test system and its potential utility in the serodiagnosis of ascariasis.

Relationship between weather and seasonal factors and trauma admission volume at a Level I trauma center

BACKGROUND

We sought to determine whether trauma patient admission volume to our Level I trauma center was correlated with observable weather or seasonal phenomena.

METHODS

Trauma registry data and national weather service data for the period between September 1, 1992, and August 31, 1998, were combined into a common data set containing trauma admission data and weather data for each day. Sequential linear regression models were constructed to determine relationships between variables in the data set.

RESULTS

There is a highly significant relationship (p < 0.00001) between maximum daily temperature and trauma admissions (R = 0.22). Rain is associated with a decrease in overall trauma volume. Rain had no effect on the number of admissions because of motor vehicle crash, however. Neither humidity nor snowfall affects trauma admission volume. Trauma admissions are significantly more frequent in July and August, and on Saturdays and Sundays (p < 0.05). Linear regression analysis identified maximum temperature, precipitation, day of week, and month as independent predictors of trauma admission volume (p < 0.001, R = 0.328).

CONCLUSION

There is a significant relationship between weather and trauma center activity; temperature and precipitation are independently associated with trauma admission volume at our institution. Statistical models of trauma incidence should consider these phenomena. Evaluation of a larger, population-based data set is needed to confirm these relationships.

Determination of the immunodominant part in the O-antigenic polysaccharide from Escherichia coli O128 by ELISA-inhibition study

The immunodominant part in the O-antigenic polysaccharide from Escherichia coli O128 was immunologically characterized by an enzyme-linked immunosorbent assay (ELISA). The antibody specificity was determined by the inhibitory effects of the methyl glycosides of constituent mono- and oligosaccharides synthesized related to the O-antigenic polysaccharide from E. coli O128. It was found that methyl alpha-L-fucopyranoside was the most effective inhibitor amongst the monosaccharides while the highest antibody specificity was directed towards the trisaccharide with the structure: beta-D-GalpNAc-(1-->6)-[alpha-L-Fucp-(1-->2)]-beta-D-Galp-1-->OMe suggesting that the monospecific antibody has the extended combining site.

Extracellular acidity potentiates AMPA receptor-mediated cortical neuronal death

The extracellular acidity that accompanies brain hypoxia-ischemia is known to reduce both NMDA and AMPA-kainate receptor-mediated currents and NMDA receptor-mediated neurotoxicity. Although a protective effect of acidic pH on AMPA-kainate receptor-mediated excitotoxicity has been assumed, such has not been demonstrated. Paradoxically, we found that lowering extracellular pH selectively increased AMPA-kainate receptor-mediated neurotoxicity in neocortical cell cultures, despite reducing peak elevations in intracellular free Ca2+. This injury potentiation may, at least in part, be related to a slowed recovery of intracellular Ca2+ homeostasis, observed after AMPA-kainate receptor activation, but not after NMDA receptor activation or exposure to high K+. The ability of acidic pH to selectively augment AMPA-kainate receptor-mediated excitotoxicity may contribute to the prominent role that these receptors play in selective neuronal death after transient global ischemia.

A cognate tRNA specific conformational change in glutaminyl-tRNA synthetase and its implication for specificity

Conformational changes that occur upon substrate binding are known to play crucial roles in the recognition and specific aminoacylation of cognate tRNA by glutaminyl-tRNA synthetase. In a previous study we had shown that glutaminyl-tRNA synthetase labeled selectively in a nonessential sulfhydryl residue by an environment sensitive probe, acrylodan, monitors many of the conformational changes that occur upon substrate binding. In this article we have shown that the conformational change that occurs upon tRNA(Gln) binding to glnRS/ATP complex is absent in a noncognate tRNA tRNA(Glu)-glnRS/ATP complex. CD spectroscopy indicates that this cognate tRNA(Gln)-induced conformational change may involve only a small change in secondary structure. The Van't Hoff plot of cognate and noncognate tRNA binding in the presence of ATP is similar, suggesting similar modes of interaction. It was concluded that the cognate tRNA induces a local conformational change in the synthetase that may be one of the critical elements that causes enhanced aminoacylation of the cognate tRNA over the noncognate ones.

Colonization of living skin equivalents by Malassezia furfur

Initial colonization events and yeast-hyphal transformation by Malassezia furfur were observed using living skin equivalent (LSE) models for growth. Yeast cells were inoculated onto the LSEs which were incubated in CO2-independent media at 37 degreesC for variable lengths of time. Assessment of fungal growth and invasion was by light- and scanning electron microscopy (SEM). Viability counts of M. furfur were determined by a method of washing and serial dilution. Yeast cells had retained their viability and increased in number approximately twofold over a 4-day period of incubation. Yeast-to-hyphal transition was not achieved in this model. Random destruction of the uppermost layers of the stratum corneum was observed in the presence of M. furfur. LSEs therefore appear to be a promising model for mechanisms of growth of cutaneous organisms.

Peripheral nerve regeneration: comparison of laminin and acidic fibroblast growth factor

PURPOSE

In an effort to show the differences between neurotrophic factors, laminin and acidic fibroblast growth factor (aFGF) were compared in terms of their abilities to regenerate axons in vivo over an extended distance.

MATERIALS AND METHODS

The sciatic nerve was transected in 15 Sprague-Dawley rats. A 15-mm Silastic tube (Dow Corning, Midland, MI) was placed between the ends of the cut nerve and filled with either laminin, aFGF, or buffer applied to collagen sponges.

RESULTS

Ten weeks postimplantation, mean axon counts showed that both laminin (2432) and aFGF (1612) produced significantly higher numbers of axons than controls (1009) (P < .05) and that laminin showed significantly more nerve regeneration than aFGF (P < .05).

CONCLUSION

These results indicate that laminin and aFGF enhance peripheral nerve regeneration across a large gap, presumably through their neurotrophic effects and mitogenic properties on supporting cells. Furthermore, it is concluded that the transient nature of aFGF's effect on the regenerative environment limits its effectiveness at regenerating axons over a prolonged period of time.

Relationship between patient-based descriptions of sinusitis and paranasal sinus computed tomographic findings

OBJECTIVE

To evaluate the relationship of paranasal sinus symptoms with coronal computed tomographic (CT) findings.

DESIGN

Prospective comparison of patient-based symptoms with imaging findings.

SETTING

Primary care and referral center office and hospital practices.

PATIENTS

Of 586 consecutive patients referred by otolaryngologists and primary care physicians for CT of the paranasal sinuses, 221 (151 women and 70 men; age range, 13-82 years; mean age, 44 years) participated by completing the Sino-Nasal Outcome Test-20 (SNOT-20) clinical questionnaire immediately before undergoing CT.

MAIN OUTCOME MEASURES

Radiologists blinded to the patients' responses scored the degree of mucosal thickening at each of 12 sites on CT scans using a staged scale of severity (0-2 points). Bivariate analysis was performed to assess the relationship between patients' symptoms and CT findings.

RESULTS

The SNOT-20 scores ranged from 0 (normal) to 78 (mean, 34). The most commonly reported symptom was fatigue. The CT scores ranged from 0 (normal) to 24 (mean, 4.07). Seventy-five patients (34%) had normal findings on the CT scan. The maxillary sinus was the most commonly involved site (96 patients, or 43%). The SNOT-20 and CT scores failed to significantly correlate (r = 0.11, P < or = .09). When the subset of patients with "positive" or "very positive" CT scans were considered, no significant correlation was observed (r = 0.12, P < or = .16). For the 132 patients reporting facial pain, the mean CT score was lower than for patients without facial pain (3.78 vs 4.78, P = .21).

CONCLUSION

Patient-based reports of paranasal sinus symptoms failed to correlate with findings on CT scans; therefore, CT should be reserved for delineating the anatomy and pattern of inflammatory paranasal disease prior to surgical intervention.

Comparison of the bonding power of various autologous fibrin tissue adhesives

OBJECTIVE

Three known autologous fibrin tissue adhesives were evaluated for bonding power on Silastic and animal and human tissues. These adhesives were also injected into living tissue to determine if any of these fibrin glues cause inflammatory or deleterious reactions when kept in living tissue for a sustained period.

METHODS

In Part I of our study, blood was drawn from 59 healthy volunteers, and autologous fibrin tissue adhesives were manufactured using the cryoprecipitation (AFTA-C), ammonium sulfate (AFTA-A), and ethanol/freezing (AFTA-E) methods. Blocks were then prepared using Silastic, porcine dermis, and human dura mater and bonded together for 10 or 30 minutes using the three adhesives. The blocks were then separated while bonding power was measured. In Part II of our study, 0.01 mL AFTA-C, AFTA-A, or AFTA-E was injected subcutaneously into the auricles of 60 rats. The rats were then killed 3, 7, 14, or 21 days later, and the auricles were examined histologically for signs of toxicity.

RESULTS

The bonding powers of AFTA-E and AFTA-C were found to be statistically similar, and both were statistically stronger than AFTA-A. The injection of AFTA-A, AFTA-E, and AFTA-C into rat auricles did not cause any adverse effects.

CONCLUSIONS

All three methods for manufacturing AFTA are effective in producing a reliable, stable fibrin glue. However, AFTA-E and AFTA-C demonstrate stronger bonding power than AFTA-A. In addition, all three forms of AFTA produce no undesirable tissue changes when injected into rat auricles.

Susceptibility to apoptosis is enhanced in immature cortical neurons

The susceptibility of cortical neurons to two forms of apoptotic death was compared with susceptibility to excitotoxic death during development in vitro (DIV 4-21). Murine cortical cultures were exposed for 48 h to the phosphatase inhibitor cyclosporine, the protein kinase inhibitor staurosporine or the excitotoxin N-methyl-D-aspartate (NMDA). Susceptibility to apoptosis induced by staurosporine or cyclosporine was maximal between DIV 4-10 and declined from DIV 10 through 18. The opposite pattern was observed with susceptibility to NMDA receptor-mediated excitotoxic necrosis, which was minimal at DIV 6 and progressively increased through DIV 21.

Structure of the O-specific side chain of the Escherichia coli O128 lipopolysaccharide

The O-specific polysaccharide isolated from Escherichia coli O128 lipopolysaccharide contains D-galactose, L-fucose, and 2-acetamido-2-deoxy-D-galactose in the molar ratios 2:1:2. The primary structure of the O-specific polysaccharide from E. coli was established by compositional analysis, methylation analysis, together with 1H and 13C NMR spectroscopy including two-dimensional shift-correlated and one-dimensional NOE spectroscopy. The polysaccharide moiety was found to consist of a tetrasaccharide backbone containing D-galactose and 2-acetamido-2-deoxy-D-galactose, with L-fucose as a side chain in a branched pentasaccharide repeating unit having the following structure: [formula: see text]

Characterization of a urea induced molten globule intermediate state of glutaminyl-tRNA synthetase from Escherichia coli

The urea-induced unfolding of glutaminyl-tRNA synthetase, a multidomain protein, has been studied by equilibrium and kinetic methods, using chemical modification, fluorescence, and CD spectroscopy. The far-UV CD, fluorescence, and sulfhydryl reactivity clearly demonstrated the existence of a stable intermediate state at around 2 M urea. The intermediate showed higher binding of 1-anilino-8-naphthalenesulfonic acid. Furthermore, near-UV CD study of the intermediate showed significantly disrupted tertiary structure with only a small change in the secondary structure, which is a characteristic of molten globule states. The activation energies (delta G++) calculated from unfolding kinetics monitored by CD and fluorescence suggest that the intermediate state may be separated from the native and the unfolded state by high activation energy barriers.

Cloning and subcellular localization of human mitochondrial hsp70

We report the cloning, nucleotide sequence, and localization of mitochondrial hsp70, a member of the human hsp70 multi-gene family. The human mthsp75 gene was cloned by screening an expression library with monoclonal antibody 3A3 that recognizes three members of the human hsp70 family (hsp70, hsc70, and a 75-kDa protein with characteristics identical to that previously established for mitochondrial hsp70). The identity of the 75-kDa protein was confirmed by subcellular fraction of HeLa cells and the demonstration that the 3A3-reactive 75-kDa protein co-fractionates with mitochondrial localized proteins. The nucleotide sequence of the respective cDNA clone revealed an open reading frame of 679 amino acids with extensive sequence identity with members of the human hsp70 family. The derived amino-terminal pre-sequence shares features common to other mitochondrial targeting sequences. The identity of the cDNA was unequivocally established by introduction of an epitope-tag at the carboxyl terminus of the cloned gene, transfection and analysis by immunofluorescence. The tagged 75-kDa protein localizes to mitochondria, thus providing conclusive evidence that it corresponds to the human mitochondrial hsp70, referred to here as mthsp75.

Determination of specificities of rabbit antisera against the O-antigenic polysaccharide from Escherichia coli O126

Rabbit polyclonal antibodies against the lipopolysaccharide of Escherichia coli O126 were serologically characterized by ELISA. The antibody specificities were determined by studying the inhibitory effects of the methyl glycosides of both anomeric configurations of the constituent monosaccharides and the oligosaccharides derived from the O-antigenic polysaccharide of E. coli O126. It was found that, amongst the monosaccharides, beta-D-N-acetyl glucosamine was the most effective inhibitory sugar in the O126 polysaccharide and the major specificity of the polyclonal antibodies was found to be directed against the trisaccharide having the structure alpha-D-Galp (1-->3)-beta-D-GlcpNAc(1-->2)-D-Manp.

Structure of the O-specific side chain of the lipopolysaccharide from Escherichia coli O126

The polysaccharide isolated from Escherichia coli O126 lipopolysaccharide contains D-galactose, D-mannose, L-fucose, and 2-acetamido-2-deoxy-D-glucose in the molar ratios 1:1:1:1. The structure of the O-antigen of the lipopolysaccharide from E. coli O126 was established by compositional analysis, partial degradation, methylation analysis, and nuclear magnetic resonance spectroscopy. These studies revealed that the O-antigen is branched and built up of tetrasaccharide repeating units having the following structure: [formula: see text]

A fluorescence spectroscopic study of substrate-induced conformational changes in glutaminyl-tRNA synthetase

Glutaminyl-tRNA synthetase from Escherichia coli is a member of a subgroup of aminoacyl-tRNA synthetases that do not catalyze ATP-PPi exchange in the absence of the cognate tRNA. Such behavior suggests conformational changes upon substrate binding. Two different fluorescent probes, pyrenylmaleimide and acrylodan, were used to specifically label a nonessential sulfhydryl group of GlnRS. Conformational changes induced by substrates were studied using glutaminyl-tRNA synthetase labeled with these two environment-sensitive probes. ATP was shown to cause a significant conformational change that alters the mode of binding to tRNA(Gln) to GlnRS. The alteration of the salt sensitivity pattern of tRNA(Gln) binding to GlnRS by ATP supports this. Binding of tRNA(Gln) causes a conformational change that may be different in nature for the ATP/GlnRS complex and free GlnRS. Hydrodynamic parameters deduced from fluorescence polarization studies and the use of a noncovalent probe indicate that the ATP-induced conformational change may not be global in character.

A fluorescence spectroscopic study of glutaminyl-tRNA synthetase from Escherichia coli and its implications for the enzyme mechanism

Interaction between Escherichia coli glutaminyl-tRNA synthetase (GlnRS) and its substrates have been studied by fluorescence quenching. In the absence of other substrates, glutamine, tRNA(Gln) and ATP bind with dissociation constants of 460, 0.22 and 180 microM, respectively. The presence of other substrates has either no effect or, at best a weak effect, on binding of ligands. Attempts to isolate enzyme-bound aminoacyl adenylate did not succeed. Binding of the phosphodiester, 5'-(methyl)adenosine monophosphate (MeAMP), to GlnRS was studied by fluorescence quenching and radioactive-ligand binding. tRNA also only has a weak effect on phosphodiester binding. Selectively pyrene-labeled GlnRS was used to obtain shape and size information for free GlnRS. A comparison with the GlnRS shape in the GlnRS/tRNA(Gln) crystal structure indicates that no major change in shape and size occurs upon tRNA(Gln) binding to GlnRS. 5,5'-Bis(8-anilino-1-naphthalene sulfonate) (bis-ANS), a non-covalent fluorescent probe, was also used to probe for conformational changes in GlnRS. This probe also indicated that no major conformational change occurs upon tRNA(Gln) binding. We conclude that lack of tRNA-independent pyrophosphate-exchange activity in this enzyme is not a result of either lack of glutamine or ATP binding in the absence of tRNA, or formation of aminoacyl adenylate and slow release of pyrophosphate. A conformational change is implied upon tRNA binding, which promotes pyrophosphate exchange. Fluorescence studies indicate that this conformational change must be limited and local in nature.