Specific and comprehensive genetic targeting reveals brain-wide distribution and synaptic input patterns of GABAergic axo-axonic interneurons

Axo-axonic cells (AACs), also called chandelier cells (ChCs) in the cerebral cortex, are the most distinctive type of GABAergic interneurons described in the neocortex, hippocampus, and basolateral amygdala (BLA). AACs selectively innervate glutamatergic projection neurons (PNs) at their axon initial segment (AIS), thus may exert decisive control over PN spiking and regulate PN functional ensembles. However, the brain-wide distribution, synaptic connectivity, and circuit function of AACs remains poorly understood, largely due to the lack of specific and reliable experimental tools. Here, we have established an intersectional genetic strategy that achieves specific and comprehensive targeting of AACs throughout the mouse brain based on their lineage (Nkx2.1) and molecular (Unc5b, Pthlh) markers. We discovered that AACs are deployed across essentially all the pallium-derived brain structures, including not only the dorsal pallium-derived neocortex and medial pallium-derived hippocampal formation, but also the lateral pallium-derived claustrum-insular complex, and the ventral pallium-derived extended amygdaloid complex and olfactory centers. AACs are also abundant in anterior olfactory nucleus, taenia tecta and lateral septum. AACs show characteristic variations in density across neocortical areas and layers and across subregions of the hippocampal formation. Neocortical AACs comprise multiple laminar subtypes with distinct dendritic and axonal arborization patterns. Retrograde monosynaptic tracing from AACs across neocortical, hippocampal and BLA regions reveal shared as well as distinct patterns of synaptic input. Specific and comprehensive targeting of AACs facilitates the study of their developmental genetic program and circuit function across brain structures, providing a ground truth platform for understanding the conservation and variation of a bona fide cell type across brain regions and species.

Occipital Nocardia Abscess Presenting With Positive Visual Phenomenon and Quadrantanopsia

ABSTRACT

A 74-year-old man with chronic obstructive pulmonary disease, glaucoma, and Stage IIIB squamous cell lung cancer experienced several minutes of flashing lights in his right visual hemifield, followed by onset of a right visual field defect. On examination, the patient had a right homonymous hemianopsia that was most dense inferiorly by confrontation testing. Emergent CT scan of the head revealed a 2.5 × 3 cm hypodensity in the left occipital lobe, which was interpreted as an acute stroke. Continuous EEG monitoring captured left posterior quadrant seizures that were temporally correlated to the positive visual phenomena. Subsequent MRI of the brain with and without contrast revealed a conglomerate of centrally necrotic and peripherally enhancing mass lesions. On biopsy, a thick purulent material was drained and Gram stain of the sample revealed gram-positive beaded rods, which speciated to Nocardia farcinica . The patient was treated with a six-week course of intravenous meropenem and a one-year course of oral trimethroprim-sulfamethoxazole. On follow-up, the patient experienced resolution of the right visual field deficit.

Single-dose combination nanovaccine induces both rapid and durable humoral immunity and toxin neutralizing antibody responses against Bacillus anthracis

Bacillus anthracis, the causative agent of anthrax, continues to be a prominent biological warfare and bioterrorism threat. Vaccination is likely to remain the most effective and user-friendly public health measure to counter this threat in the foreseeable future. The commercially available AVA BioThrax vaccine has a number of shortcomings where improvement would lead to a more practical and effective vaccine for use in the case of an exposure event. Identification of more effective adjuvants and novel delivery platforms is necessary to improve not only the effectiveness of the anthrax vaccine, but also enhance its shelf stability and ease-of-use. Polyanhydride particles have proven to be an effective platform at adjuvanting the vaccine-associated adaptive immune response as well as enhancing stability of encapsulated antigens. Another class of adjuvants, the STING pathway-targeting cyclic dinucleotides, have proven to be uniquely effective at inducing a beneficial inflammatory response that leads to the rapid induction of high titer antibodies post-vaccination capable of providing protection against bacterial pathogens. In this work, we evaluate the individual contributions of cyclic di-GMP (CDG), polyanhydride nanoparticles, and a combination thereof towards inducing neutralizing antibody (nAb) against the secreted protective antigen (PA) from B. anthracis. Our results show that the combination nanovaccine elicited rapid, high titer, and neutralizing IgG anti-PA antibody following single dose immunization that persisted for at least 108 DPI.

HIV-Risk Behavior Among Adults with Opioid Use Disorder During 12 Months Following Pre-trial Detention: Results from a Randomized Trial of Methadone Treatment

This was a three group randomized clinical trial of interim methadone and patient navigation involving 225 pre-trial detainees with opioid use disorder in Baltimore. The HIV Risk Assessment Battery (RAB) was administered at baseline (in jail), and at 6 and 12 months post-release. Generalized linear mixed model analyses indicated the condition × time interaction effect failed to reach significance (ps > .05) for both the drug risk and sex risk subscale scores. Therefore, findings suggest that there were no intervention effects on drug or sex risk behaviors. However, increased use of cocaine at baseline was associated with increases in drug- (b = .04, SE = .02) and sex-risk (b = .01, SE = .003) behaviors. These results suggest that interventions targeting cocaine use among pre-trial detainees may serve as a means of reducing HIV risk associated with drug- and sex-risk behaviors.Clinical Trials Registration: Clinicaltrials.gov NCT02334215.

Polymeric Nanoparticle-Based Vaccine Adjuvants and Delivery Vehicles

As vaccine formulations have progressed from including live or attenuated strains of pathogenic components for enhanced safety, developing new adjuvants to more effectively generate adaptive immune responses has become necessary. In this context, polymeric nanoparticles have emerged as a promising platform with multiple advantages, including the dual capability of adjuvant and delivery vehicle, administration via multiple routes, induction of rapid and long-lived immunity, greater shelf-life at elevated temperatures, and enhanced patient compliance. This comprehensive review describes advances in nanoparticle-based vaccines (i.e., nanovaccines) with a particular focus on polymeric particles as adjuvants and delivery vehicles. Examples of the nanovaccine approach in respiratory infections, biodefense, and cancer are discussed.

Development of a subcutaneous ear implant to deliver an anaplasmosis vaccine to dairy steers

Bovine anaplasmosis is the most prevalent tick-transmitted disease of cattle worldwide and a major obstacle to profitable beef production. Use of chlortetracycline-medicated feed to control active anaplasmosis infections during the vector season has raised concerns about the potential emergence of antimicrobial resistance in bacteria that may pose a risk to human health. Furthermore, the absence of effectiveness data for a commercially available, conditionally licensed anaplasmosis vaccine is a major impediment to implementing anaplasmosis control programs. The primary objective of this study was to develop a single-dose vaccine delivery platform to produce long-lasting protective immunity against anaplasmosis infections. Twelve Holstein steers, aged 11 to 12 wk, were administered a novel 3-stage, single-dose vaccine against Anaplasma marginale, a major surface protein 1a. The vaccine consisted of a soluble vaccine administered subcutaneously (s.c.) for immune priming, a vaccine depot of a biodegradable polyanhydride rod with intermediate slow release of the vaccine for boosting immune response, and an immune-isolated vaccine platform for extended antigen release (VPEAR implant) deposited s.c. in the ear. Six calves were randomly assigned to 2 vaccine constructs (n = 3) that featured rods and implants containing a combination of 2 different adjuvants, diethylaminoethyl (DEAE)-Dextran and Quil-A (Group A). The remaining 6 calves were randomly assigned to 2 vaccine constructs (n = 3) that featured rods and implants containing the same adjuvant (either DEAE-Dextran or Quil A) (Group B). Twenty-one months post-implantation, calves were challenged intravenously with A. marginale stabilate and were monitored weekly for signs of fever, decreased packed cell volume (PCV) and bacteremia. Data were analyzed using a mixed-effects model and chi-squared tests (SAS v9.04.01, SAS Institute, Cary, NC). Calves in Group A had higher PCV than calves in Group B (P = 0.006) at day 35 post-infection. Calves in Group A were less likely to require antibiotic intervention compared with calves in Group B (P = 0.014). Results indicate that calves exhibited diminished clinical signs of anaplasmosis when antigen was delivered with a combination of adjuvants as opposed to a single adjuvant. This demonstrates the feasibility of providing long-lasting protection against clinical bovine anaplasmosis infections using a subcutaneous ear implant vaccine construct.

Synthesis and Characterization of Rapidly Degrading Polyanhydrides as Vaccine Adjuvants

There is a currently a need to develop adjuvants that are best suited to simultaneously enhance immune responses, induce immunologic memory, improve patient compliance (i.e., reduce doses and inflammation), and provide vaccine shelf stability for stockpiling and global deployment to challenging environments. Biodegradable polyanhydrides have been investigated extensively to overcome such challenges. It has been shown that controlling copolymer composition can result in chemistry-dependent immunomodulatory capabilities. These studies have revealed that copolymers rich in sebacic acid (SA) are highly internalized by antigen presenting cells and confer improved shelf stability of encapsulated proteins, while copolymers rich in 1,8-bis(p-carboxyphenoxy)-3,6-dioxaoctane (CPTEG) also exhibit enhanced internalization by and activation of antigen presenting cells (APCs), in addition to providing superior retention of protein stability following encapsulation and release. However, to date, CPTEG:SA copolymers have not been synthesized and described. In this work, we hypothesized that new copolymers composed of CPTEG and SA would combine the advantages of both monomers in terms of enhanced thermal properties, maintaining antigenicity of encapsulated proteins following nanoparticle synthesis, and superior cellular internalization and activation by APCs, demonstrated by the upregulation of costimulatory markers CD80, CD86, and CD40, as well as the secretion of proinflammatory cytokines IL-6, IL-1β, and TNF-α. Herein, we describe the synthesis and design of novel CPTEG:SA nanoparticles with improved thermal properties, payload stability, and internalization by antigen presenting cells for applications in vaccine delivery. The performance of these new CPTEG:SA formulations was compared to that of traditional polyanhydride copolymers.

Single-dose combination nanovaccine induces both rapid and long-lived protection against pneumonic plague

Yersinia pestis, the causative agent of pneumonic plague, induces a highly lethal infection if left untreated. Currently, there is no FDA-approved vaccine against this pathogen; however, USAMRIID has developed a recombinant fusion protein, F1-V, that has been shown to induce protection against pneumonic plague. Many F1-V-based vaccine formulations require prime-boost immunization to achieve protective immunity, and there are limited reports of rapid induction of protective immunity (≤ 14 days post-immunization (DPI)). The STimulator of INterferon Genes agonists cyclic dinucleotides (CDNs) have been shown to be promising vaccine adjuvants. Polyanhydride nanoparticle-based vaccines (i.e., nanovaccines) have also shown to enhance immune responses due to their dual functionality as adjuvants and delivery vehicles. In this work, a combination nanovaccine was designed that comprised F1-V-loaded nanoparticles combined with the CDN, dithio-RP,RP-cyclic di-guanosine monophosphate, to induce rapid and long-lived protective immunity against pneumonic plague. All mice immunized with a single dose combination nanovaccine were protected from Y. pestis lethal challenge within 14 DPI and demonstrated enhanced protection over F1-V adjuvanted with CDNs alone at challenge doses ≥7000 CFU Y. pestis CO92. In addition, 75% of mice receiving the single dose of the combination nanovaccine were protected from challenge at 182 DPI, while maintaining high levels of antigen-specific serum IgG. ELISPOT analysis of vaccinated animals at 218 DPI revealed F1-V-specific long-lived plasma cells in bone marrow in mice vaccinated with CDN adjuvanted F1-V or the combination nanovaccine. Microarray analysis of serum from these vaccinated mice revealed the presence of serum antibody that bound to a broad range of F1 and V linear epitopes. These results demonstrate that combining the adjuvanticity of CDNs with a nanovaccine delivery system enables induction of both rapid and long-lived protective immunity against Y. pestis. STATEMENT OF SIGNIFICANCE: • Yersinia pestis, the causative agent of pneumonic plague, induces a highly lethal infection if left untreated. Currently, there is no FDA-approved vaccine against this biodefense pathogen. • We designed a combination nanovaccine comprising of F1-V antigen-loaded polyanhydride nanoparticles and a cyclic dinucleotide adjuvant to induce both rapid and long-lived protective immunity against pneumonic plague. • Animals immunized with the combination nanovaccine maintained high levels of antigen-specific serum IgG and long-lived plasma cells in bone marrow and the serum antibody showed a high affinity for a broad range of F1 and V linear epitopes. • The combination nanovaccine is a promising next-generation vaccine platform against weaponized Y. pestis based on its ability to induce both rapid and long-lived protective immunity.

Stereocontrolled Synthesis of Arylomycin-Based Gram-Negative Antibiotic GDC-5338

We report herein an efficient, stereocontrolled, and chromatography-free synthesis of the novel broad spectrum antibiotic GDC-5338. The route features the construction of a functionalized tripeptide backbone, a high-yielding macrocyclization via a Pd-catalyzed Suzuki-Miyaura reaction, and the late-stage elaboration of key amide bonds with minimal stereochemical erosion. Through extensive reaction development and analytical understanding, these key advancements allowed the preparation of GDC-5338 in 17 steps, 15% overall yield, >99 A % HPLC, and >99:1 dr.

Sustained antigen release polyanhydride-based vaccine platform for immunization against bovine brucellosis

Brucellosis is a bacterial zoonosis and a significant source of economic loss and a major public health concern, worldwide. Bovine brucellosis, as caused primarily by Brucella abortus, is an important cause of reproductive loss in cattle. Vaccination has been the most effective way to reduce disease prevalence contributing to the success of control and eradication programs. Currently, there are no human vaccines available, and despite the success of commercial vaccines for livestock, such as B. abortus strain RB51 (RB51), there is need for development of novel and safer vaccines against brucellosis. In the current study, we report the fabrication of and immune responses to an implantable single dose polyanhydride-based, methanol-killed RB51 antigen containing delivery platform (VPEAR) in cattle. In contrast to animals vaccinated with RB51, we did not observe measurable RB51-specific IFN-γ or IgG responses in the peripheral blood, following initial vaccination with VPEAR. However, following a subsequent booster vaccination with RB51, we observed an anamnestic response in both vaccination treatments (VPEAR and live RB51). The magnitude and kinetics of CD4+ IFN-γ-mediated responses and circulating memory T cell subpopulations were comparable between the two vaccination treatments. Additionally, IgG titers were significantly increased in animals vaccinated with VPEAR as compared to live RB51- vaccinated animals. These data demonstrate that killed antigen may be utilized to generate and sustain memory, IFN-γ-mediated, CD4+ T cell and humoral responses against Brucella in a natural host. To our knowledge, this novel approach to vaccination against intracellular bacteria, such as Brucella, has not been reported before.

STING pathway stimulation results in a differentially activated innate immune phenotype associated with low nitric oxide and enhanced antibody titers in young and aged mice

BACKGROUND

One of the most concerning public health issues, related to vaccination and disease prevention, is the inability to induce durable immune responses following a single-dose immunization. In this regard, the nature of the inflammatory environment induced by vaccine adjuvants can negatively impact the resulting immune response. To address these concerns, new strategies to vaccine design are needed in order to improve the outcomes of immune responses, particularly in immunologically disadvantaged populations.

METHODS

Comparisons of the scope of innate immune activation induced by TLR agonists versus cyclic dinucleotides (CDNs) was performed. Their effects on the activation characteristics (e.g., metabolism, cytokine secretion) of bone marrow derived dendritic cells (BMDCs) were studied. In addition, the differential effects on in vivo induction of antibody responses were measured.

RESULTS

As compared to TLR ligands, the stimulation of BMDCs with CDNs induced distinctly different metabolic outcomes. Marked differences were observed in the production of nitric oxide (NO) and the cytokine BAFF. These distinct differences were correlated with improved (i.e., more rapid and persistent) vaccine antibody responses in both aged and young mice.

CONCLUSIONS

Our results illustrate that the innate immune pathway targeted by adjuvants can critically impact the outcome of the immune response post-vaccination. Specifically, CDN stimulation of APCs induced an activation phenotype that was characterized by decreased innate effector molecule production (e.g., NO) and increased BAFF. This was attributed to the induction of an innate inflammatory environment that enabled the host to make the most of the existing B lymphocyte potential. The use of adjuvants that differentially engage mechanisms of innate immune activation would be particularly advantageous for the generation of robust, single dose vaccines. The results of this study demonstrated that CDNs induced differential innate activation and enhanced vaccine induced antibody responses in both young and aged mice.

Radial Glial Lineage Progression and Differential Intermediate Progenitor Amplification Underlie Striatal Compartments and Circuit Organization

The circuitry of the striatum is characterized by two organizational plans: the division into striosome and matrix compartments, thought to mediate evaluation and action, and the direct and indirect pathways, thought to promote or suppress behavior. The developmental origins of these organizations and their developmental relationships are unknown, leaving a conceptual gap in understanding the cortico-basal ganglia system. Through genetic fate mapping, we demonstrate that striosome-matrix compartmentalization arises from a lineage program embedded in lateral ganglionic eminence radial glial progenitors mediating neurogenesis through two distinct types of intermediate progenitors (IPs). The early phase of this program produces striosomal spiny projection neurons (SPNs) through fate-restricted apical IPs (aIPSs) with limited capacity; the late phase produces matrix SPNs through fate-restricted basal IPs (bIPMs) with expanded capacity. Notably, direct and indirect pathway SPNs arise within both aIPS and bIPM pools, suggesting that striosome-matrix architecture is the fundamental organizational plan of basal ganglia circuitry.

Room Temperature Stable PspA-Based Nanovaccine Induces Protective Immunity

Streptococcus pneumoniae is a major causative agent of pneumonia, a debilitating disease particularly in young and elderly populations, and is the leading worldwide cause of death in children under the age of five. While there are existing vaccines against S. pneumoniae, none are protective across all serotypes. Pneumococcal surface protein A (PspA), a key virulence factor of S. pneumoniae, is an antigen that may be incorporated into future vaccines to address the immunological challenges presented by the diversity of capsular antigens. PspA has been shown to be immunogenic and capable of initiating a humoral immune response that is reactive across approximately 94% of pneumococcal strains. Biodegradable polyanhydrides have been studied as a nanoparticle-based vaccine (i.e., nanovaccine) platform to stabilize labile proteins, to provide adjuvanticity, and enhance patient compliance by providing protective immunity in a single dose. In this study, we designed a room temperature stable PspA-based polyanhydride nanovaccine that eliminated the need for a free protein component (i.e., 100% encapsulated within the nanoparticles). Mice were immunized once with the lead nanovaccine and upon challenge, presented significantly higher survival rates than animals immunized with soluble protein alone, even with a 25-fold reduction in protein dose. This lead nanovaccine formulation performed similarly to protein adjuvanted with Alum, however, with much less tissue reactogenicity at the site of immunization. By eliminating the free PspA from the nanovaccine formulation, the lead nanovaccine was efficacious after being stored dry for 60 days at room temperature, breaking the need for maintaining the cold chain. Altogether, this study demonstrated that a single dose PspA-based nanovaccine against S. pneumoniae induced protective immunity and provided thermal stability when stored at room temperature for at least 60 days.

Nucleophilic Aromatic Substitution Reactions in Water Enabled by Micellar Catalysis

Given the huge dependence on dipolar, aprotic solvents such as DMF, DMSO, DMAc, and NMP in nucleophilic aromatic substitution reactions (SNAr), a simple and environmentally friendly alternative is reported. Use of a "benign-by-design" nonionic surfactant, TPGS-750-M, in water enables nitrogen, oxygen, and sulfur nucleophiles to participate in SNAr reactions. Aromatic and heteroaromatic substrates readily participate in this micellar catalysis, which takes place at or near ambient temperatures.

Daclatasvir inhibits hepatitis C virus NS5A motility and hyper-accumulation of phosphoinositides

Combinations of direct-acting antivirals (DAAs) against the hepatitis C virus (HCV) have the potential to revolutionize the HCV therapeutic regime. An integral component of DAA combination therapies is HCV NS5A inhibitors. It has previously been proposed that NS5A DAAs inhibit two functions of NS5A: RNA replication and virion assembly. In this study, we characterize the impact of a prototype NS5A DAA, daclatasvir (DCV), on HCV replication compartment formation. DCV impaired HCV replicase localization and NS5A motility. In order to characterize the mechanism behind altered HCV replicase localization, we examined the impact of DCV on the interaction of NS5A with its essential cellular cofactor, phosphatidylinositol-4-kinase III α (PI4KA). We observed that DCV does not inhibit PI4KA directly, nor does it impair early events of the NS5A-PI4KA interaction that can occur when NS5A is expressed alone. NS5A functions that are unaffected by DCV include PI4KA binding, as determined by co-immunoprecipitation, and a basal accumulation of the PI4KA product, PI4P. However, DCV impairs late steps in PI4KA activation that requires NS5A expressed in the context of the HCV polyprotein. These NS5A functions include hyper-stimulation of PI4P levels and appropriate replication compartment formation. The data are most consistent with a model wherein DCV inhibits conformational changes in the NS5A protein or protein complex formations that occur in the context of HCV polyprotein expression and stimulate PI4P hyper-accumulation and replication compartment formation.

Chemoselective reductions of nitroaromatics in water at room temperature

A robust and green protocol for the reduction of functionalized nitroarenes to the corresponding primary amines has been developed. It relies on inexpensive zinc dust in water containing nanomicelles derived from the commercially available designer surfactant TPGS-750-M. This mild process takes place at room temperature and tolerates a wide range of functionalities. Highly selective reductions can also be achieved in the presence of common protecting groups.

Antibacterial effects of theaflavin and synergy with epicatechin against clinical isolates of Acinetobacter baumannii and Stenotrophomonas maltophilia

Stenotrophomonas maltophilia and Acinetobacter baumannii are recognised as important nosocomial pathogens; however, due to their intrinsic resistance to multiple antibiotics, treatment options are limited. Polyphenols from black tea have been shown to possess antibacterial action. In this study, the antibacterial effects of various concentrations of theaflavin as well as combinations of theaflavin and epicatechin were determined using the disk diffusion assay. The results showed strong antibacterial activity of theaflavin against eight clinical isolates of S. maltophilia and A. baumannii. Significant synergy (P≤0.05) was also observed between theaflavin and epicatechin against all isolates. Although the mechanisms for this activity and synergy are not well understood, the clinical potential is clear and further research is recommended to determine the modes of action.

Dinoxin B, a withanolide from Datura inoxia leaves with specific cytotoxic activities

A new withanolide, dinoxin B (12,21-dihydroxy-1-oxowitha-2,5,24-trienolide-27-O-β-D-glucopyranoside, 1), was isolated from a methanol extract of Datura inoxia leaves, using bioassay-guided fractionation. The structure was determined by spectroscopic techniques, including (1)H, (13)C, and 2D NMR experiments as well as by HRMS. Extracts and the purified compound were tested for their antiproliferative activities toward a panel of human normal and cancer cell lines. Dinoxin B (1) and its aglycone (2) exhibited submicromolar IC(50) values against multiple human cancer cell lines. Among the most sensitive were several breast cancer cell lines. Dinoxin B (1) was found only in D. inoxia and was not detected in D. metel or D. stramonium. The accumulation of this compound was limited largely to leaf tissue, with little to none detected in extracts from the flowers, fruits, roots, or stems of D. inoxia.

SMAD signaling drives heart and muscle dysfunction in a Drosophila model of muscular dystrophy

Loss-of-function mutations in the genes encoding dystrophin and the associated membrane proteins, the sarcoglycans, produce muscular dystrophy and cardiomyopathy. The dystrophin complex provides stability to the plasma membrane of striated muscle during muscle contraction. Increased SMAD signaling due to activation of the transforming growth factor-β (TGFβ) pathway has been described in muscular dystrophy; however, it is not known whether this canonical TGFβ signaling is pathogenic in the muscle itself. Drosophila deleted for the γ/δ-sarcoglycan gene (Sgcd) develop progressive muscle and heart dysfunction and serve as a model for the human disorder. We used dad-lacZ flies to demonstrate the signature of TGFβ activation in response to exercise-induced injury in Sgcd null flies, finding that those muscle nuclei immediately adjacent to muscle injury demonstrate high-level TGFβ signaling. To determine the pathogenic nature of this signaling, we found that partial reduction of the co-SMAD Medea, homologous to SMAD4, or the r-SMAD, Smox, corrected both heart and muscle dysfunction in Sgcd mutants. Reduction in the r-SMAD, MAD, restored muscle function but interestingly not heart function in Sgcd mutants, consistent with a role for activin but not bone morphogenic protein signaling in cardiac dysfunction. Mammalian sarcoglycan null muscle was also found to exhibit exercise-induced SMAD signaling. These data demonstrate that hyperactivation of SMAD signaling occurs in response to repetitive injury in muscle and heart. Reduction of this pathway is sufficient to restore cardiac and muscle function and is therefore a target for therapeutic reduction.

Ultrasensitive detection and characterization of biomolecules using superchiral fields

The spectroscopic analysis of large biomolecules is important in applications such as biomedical diagnostics and pathogen detection, and spectroscopic techniques can detect such molecules at the nanogram level or lower. However, spectroscopic techniques have not been able to probe the structure of large biomolecules with similar levels of sensitivity. Here, we show that superchiral electromagnetic fields, generated by the optical excitation of plasmonic planar chiral metamaterials, are highly sensitive probes of chiral supramolecular structure. The differences in the effective refractive indices of chiral samples exposed to left- and right-handed superchiral fields are found to be up to 10(6) times greater than those observed in optical polarimetry measurements, thus allowing picogram quantities of adsorbed molecules to be characterized. The largest differences are observed for biomolecules that have chiral planar sheets, such as proteins with high β-sheet content, which suggests that this approach could form the basis for assaying technologies capable of detecting amyloid diseases and certain types of viruses.

Interdomain mobility and conformational stability of type III fibronectin domain pairs control surface adsorption, desorption and unfolding

The 9th-10th type III fibronectin domain pair (9-10FNIII) has found widespread use as a biomimetic surface for cell adhesion. However, the effect of mutations to 9-10FNIII on its surface adsorption characteristics have not been investigated. Here we address this issue using total internal reflection fluorescence (TIRF) and circular dichroism spectroscopy, comparing two conformationally stable 9-10FNIII mutants against the wild type. Desorption of the 9-10FNIII mutants from the silica surface was minimal in comparison to desorption of 9-10FNIII. The extent and rate of protein desorption from silica was empirically matched by loss of secondary structure upon adsorption, with only the spectrum for 9-10FNIII showing extensive loss of the beta-sandwich fold. For the proteins adsorbed to hydrophobic surfaces, only the CD spectra for the 9-10FNIII mutant constrained via an interdomain disulphide bridge showed similarity with the corresponding solution structure. Since the binding of 9-10FNIII to integrin alpha5beta1 is highly dependent on the relative spatial arrangement of the two domains, we suggest that the observed differences in cell adhesion and spreading on wild type 9-10FNIII and mutants may in part be attributed to the extent of protein desorption and unfolding at the surface.

Solution formulation and lyophilisation of a recombinant fibronectin fragment

The 9th-10th type III fibronectin domain pair shows promise in tissue engineering and tumour vasculature targeting. Calorimetry and structure-function analysis were used to investigate the effects of solution formulation and lyophilisation of a mutant ((9-10)FNIII-P). A single endothermic transition for (9-10)FNIII-P in solution was observed at pH<8, irrespective of addition of sucrose or PEG. The temperature at the maximum heat capacity (T(m)) and enthalpy (deltaH) of the transition increased for increasing sucrose concentrations but decreased for increasing PEG concentrations. The transition was fitted to a single two-state unfolding mechanism (in contrast to unfolding in guanidine. x HCl) and was partially reversible only at pH 4, with increasing concentrations of sucrose causing a marked fall in deltaH between scans. Circular dichroism spectra for the thermal unfolding of (9-10)FNIII-P at pH 4 showed loss of native beta-sheet structure and loss of aromatic contributions to the peak centred around 226 nm yielding an intermediate conformation, which in the presence of sucrose was more disordered. Despite a glass transition (T(g)') for (9-10)FNIII-P(aq) of -70 degrees C, primary drying at -30 degrees C did not perturb its conformation upon reconstitution or its biological activity following lyophilisation; the addition of sucrose or PEG had no influence on structure or activity. The main consideration in the formulation of (9-10)FNIII-P was therefore pH.

Regulation of ubiquitin-proteasome system mediated degradation by cytosolic stress

ER-associated, ubiquitin-proteasome system (UPS)-mediated degradation of the wild-type (WT) gap junction protein connexin32 (Cx32) is inhibited by mild forms of cytosolic stress at a step before its dislocation into the cytosol. We show that the same conditions (a 30-min, 42 degrees C heat shock or oxidative stress induced by arsenite) also reduce the endoplasmic reticulum (ER)-associated turnover of disease-causing mutants of Cx32 and the cystic fibrosis transmembrane conductance regulator (CFTR), as well as that of WT CFTR and unassembled Ig light chain. Stress-stabilized WT Cx32 and CFTR, but not the mutant/unassembled proteins examined, could traverse the secretory pathway. Heat shock also slowed the otherwise rapid UPS-mediated turnover of the cytosolic proteins myoD and GFPu, but not the degradation of an ubiquitination-independent construct (GFP-ODC) closely related to the latter. Analysis of mutant Cx32 from cells exposed to proteasome inhibitors and/or cytosolic stress indicated that stress reduces degradation at the level of substrate polyubiquitination. These findings reveal a new link between the cytosolic stress-induced heat shock response, ER-associated degradation, and polyubiquitination. Stress-denatured proteins may titer a limiting component of the ubiquitination machinery away from pre-existing UPS substrates, thereby sparing the latter from degradation.

Tight junction modulation and biochemical characterisation of the zonula occludens toxin C-and N-termini

The ZOT N-terminal domain was expressed and refolded, yielding a soluble protein with defined secondary structure. Although distantly related to protein I of filamentous phages, no evidence of ATPase activity was found. It is therefore unlikely that the ZOT N-terminal domain is involved in cholera toxin phage packaging in Vibrio cholerae. The ZOT C-terminal domain caused delocalisation of occludin and ZO-1 from Caco-2 cell-cell contacts, irrespective of disulfide bridge formation in its putative binding domain. However, the C-terminal domain did not cause actin reorganisation and this may explain the absence of a concomitant reduction in the transepithelial electrical resistance across cell monolayers.

A Full-Color Electroluminescent Device and Patterned Photoalignment Using Light-Emitting Liquid Crystals

Blue, green, and red polymerizable light-emitting liquid crystals have been patterned photolithographically in a full-color liquid-crystal electroluminescent display. A new hole-transporting photoalignment copolymer is also reported and the spatial patterning of the polarization direction of emission is demonstrated.

Rifaximin-ciprofloxacin combination therapy is effective in chronic active refractory pouchitis

OBJECTIVE

Treatment of chronic refractory pouchitis is often difficult and disappointing and some of the affected pouches subsequently fail. This study was conducted to evaluate the efficacy and tolerability of treatment with rifaximin, a nonabsorbable oral antibiotic with immunomdulatory functions, in combination with ciprofloxacin for chronic active refractory pouchitis.

PATIENTS AND METHODS

Eight patients with chronic active refractory pouchitis were treated orally with a combination of rifaximin 1 g b.d and ciprofloxacin 500 mg b.d. for two weeks. Clinical assessment, endoscopic and histological evaluations were performed before and after therapy using the Pouchitis Disease Activity Index (PDAI) score. Improvement was defined as a decrease of at least three points in the PDAI score and remission as a PDAI score of 0. The Wilcoxon signed rank test was used to compare pre- and post-treatment PDAI scores. The long-term outcome of the treated patients was prospectively monitored.

RESULTS

Seven of the eight patients either went into remission (n = 5) or improved (n = 2). The median (range) PDAI scores before and after therapy were 12 (9-18) and 0 (0-15), respectively, (P = 0.018). All patients were compliant and no side effects were reported. Pouchitis recurred in two of the seven responding patients but returned into remission after further courses of the same combination. After a median follow-up of 30 months, the seven responding patients still had satisfactory pouch function.

CONCLUSION

Rifaximin-ciprofloxacin combination therapy is safe and objectively effective in chronic active refractory pouchitis and may salvage a significant percentage of 'at risk pouches'.

The cryobiology of assisted reproduction

Cryopreservation of human gametes and embryos has become an integral part of assisted reproduction. The major developments in cryopreservation technology have mirrored the rapid expansion of reproductive technology over the past 2 decades. It is now possible to cryopreserve sperm, oocytes and embryos at their various stages of development. The introduction of vitrification and rapid freezing techniques is gaining widespread recognition and may become the method of choice over traditional slow freezing methods. Ovarian tissue cryopreservation offers the hope of fertility preservation for women who are faced with potentially sterilizing medical or surgical treatments. Paralleling the introduction of cryobiology to assisted reproduction has been the realization of a number of moral and ethical issues related to gamete and/or embryo storage.

Arteriovenous malformation of the uterus associated with secondary postpartum hemorrhage

We present the case of a young woman with persistent secondary postpartum hemorrhage. Transvaginal imaging demonstrated an irregular pulsatile lesion in the anterior myometrium. Color Doppler analysis revealed the presence of abnormal vessels consistent with an arteriovenous malformation. Typically this vascular abnormality had a turbulent pattern of arterial and venous flow with high peak velocities and low resistance. The patient was treated with selective arterial embolization leading to a full recovery.

Modulation of smooth muscle phenotype in vitro by homologous cell substrate

We have developed a novel cell culture system that supports the shortening of smooth muscle cells. Primary rat airway smooth muscle cells were plated on an ethanol-fixed, confluent monolayer of homologous smooth muscle cells (homologous cell substrate, HCS). Cells grown on HCS exhibited morphological and functional characteristics consistent with a differentiated phenotype. Cells on HCS were spindle shaped with a well-defined long axis, whereas cells grown on glass were larger and irregularly shaped. Smooth muscle-specific alpha-actin immunostained diffusely in cells on HCS, whereas it appeared as stress fibers in cells on glass. Agonists recruited a greater fraction of HCS cells to contract, resulting in greater changes in cell area or length on average, but the maximal capacity of shortening of individual cells was similar between the groups. Unlike cells on glass, cells on HCS shortened to methacholine. HCS was reversible and persisted over several passages. Agonists stimulated intracellular Ca(2+) oscillations in cells on HCS, whereas they elicited biphasic peak and plateau transients in cells on glass. HCS modulates smooth muscle cell phenotype in vitro.

N-linked glycosylation and sequence changes in a critical negative control region of the ASCT1 and ASCT2 neutral amino acid transporters determine their retroviral receptor functions

A widely dispersed interference group of retroviruses that includes the feline endogenous virus (RD114), baboon endogenous virus (BaEV), human endogenous virus type W (HERV-W), and type D primate retroviruses uses the human Na(+)-dependent neutral amino acid transporter type 2 (hASCT2; gene name, SLC1A5) as a common cell surface receptor. Although hamster cells are fully resistant to these viruses and murine cells are susceptible only to BaEV and HERV-W pseudotype viruses, these rodent cells both become highly susceptible to all of the viruses after treatment with tunicamycin, an inhibitor of protein N-linked glycosylation. A partial explanation for these results was recently provided by findings that the orthologous murine transporter mASCT2 is inactive as a viral receptor, that a related (ca. 55% identity) murine paralog (mASCT1; gene name, SLC1A4) mediates infections specifically of BaEV and HERV-W, and that N-deglycosylation of mASCT1 activates it as a receptor for all viruses of this interference group. Because the only two N-linked oligosaccharides in mASCT1 occur in the carboxyl-terminal region of extracellular loop 2 (ECL2), it was inferred that this region contributes in an inhibitory manner to infections by RD114 and type D primate viruses. To directly and more thoroughly investigate the receptor active sites, we constructed and analyzed a series of hASCT2/mASCT2 chimeras and site-directed mutants. Our results suggest that a hypervariable sequence of 21 amino acids in the carboxyl-terminal portion of ECL2 plays a critical role in determining the receptor properties of ASCT2 proteins for all viruses in this interference group. In addition, we analyzed the tunicamycin-dependent viral susceptibility of hamster cells. In contrast to mASCT1, which contains two N-linked oligosaccharides that partially restrict viral infections, hamster ASCT1 contains an additional N-linked oligosaccharide clustered close to the others in the carboxyl-terminal region of ECL2. Removal of this N-linked oligosaccharide by mutagenesis enabled hamster ASCT1 to function as a receptor for all viruses of this interference group. These results strongly suggest that combinations of amino acid sequence changes and N-linked oligosaccharides in a critical carboxyl-terminal region of ECL2 control retroviral utilization of both the ASCT1 and ASCT2 receptors.

A prospective, comparative study of the para-aminobenzoic acid test and faecal elastase 1 in the assessment of exocrine pancreatic function

BACKGROUND

The assessment of exocrine pancreatic insufficiency is part of the routine work-up of patients with persistent diarrhoea or suspected steatorrhoea. Direct and indirect tests for the diagnosis of exocrine pancreatic insufficiency have their drawbacks. Measurement of faecal elastase 1 by enzyme-linked immunoabsorbent assay is a simple, non-invasive, robust test for exocrine pancreatic insufficiency.

METHODS

We performed a prospective comparison of the para-aminobenzoic acid test and faecal elastase 1 test in 45 patients being investigated for diarrhoea or suspected steatorrhoea. Details of clinical suspicion, imaging and response to treatment were recorded.

RESULTS

Exocrine pancreatic function was normal in 20 patients with normal para-aminobenzoic acid and faecal elastase 1 levels. Eight patients had exocrine pancreatic insufficiency with low para-aminobenzoic acid and faecal elastase 1 levels, which improved with enzyme supplementation. In 14 of the 15 patients with low or borderline low para-aminobenzoic acid and normal faecal elastase 1 levels, a non-pancreatic cause was found; one patient had a false positive para-aminobenzoic acid test. Two had normal para-aminobenzoic acid but low faecal elastase 1 levels. One improved with pancreatic supplementation, and imaging revealed chronic pancreatitis. The other had a false positive faecal elastase 1 test related to profuse diarrhoea.

CONCLUSIONS

Faecal elastase 1 estimation is a simple, non-invasive, robust test of exocrine pancreatic insufficiency, performed on an out-patient stool sample. Its diagnostic performance is superior to that of the para-aminobenzoic acid test in investigating patients with diarrhoea or suspected steatorrhoea.

CdTe nanocrystals: synthesis, optical characterization, and pseudopotential calculation of the band gap

CdTe nanocrystals were synthesized in aqueous solution using 1-thioglycerol and 2-mercaptoethanol as surface stabilizers. The nanocrystals were characterized by means of X-ray powder diffraction and UV-vis absorption measurements. The UV-vis absorption spectra exhibit two distinct transition lines. Comparison of the experimental measurements with the results of the empirical pseudopotential calculations of the CdTe nanocrystals showed that the lower energy absorption line can be assigned to the heavy-hole exciton transition, whereas the higher energy absorption line can be attributed to the light-hole exciton transition.

Investigation of the infertile couple: a one-stop ultrasound-based approach

The appropriateness of many investigations for subfertility will continue to be of debate for some time yet. Of most benefit to the concerned couple would be a process that is diagnostically accurate, expeditious and reliable. It should be performed with a minimum of invasion and provide both patient and clinician with useful prognostic information regarding possible future treatment. This article is intended to illustrate the advantages of an ultrasound-based process of subfertility investigation. Discussed is the role of ultrasound compared with more invasive investigative methods such as laparoscopy and hysteroscopy. In addition, the potential capacity of newer advanced ultrasound technologies is reviewed.

The investigation of an equilibrium dependent reaction for the formation of enamines in a microchemical system

The paper describes the equilibrium dependant reaction for the formation of enamines in a microchemical system utilising electroosmotic flow (EOF) for fluid mobilisation. The authors have shown that the reaction can be carried out without the presence of a Lewis acid catalyst, in addition the enamine intermediate was synthesised at room temperature using mild solvent conditions. A 42% conversion of cyclohexanone into the enamine has been achieved to date.

Mutagenic and chemical modification of the ABA-1 allergen of the nematode Ascaris: consequences for structure and lipid binding properties

The polyprotein allergens/antigens of nematodes (NPAs) are the only lipid binding proteins known to be produced as polyproteins. Cleavage of the large polyprotein precursors at regularly spaced proteinase cleavage sites produces 10 or 11 individual protein units of approximately 15 kDa. The sequences of these units are highly diverse within and between species, but there are five absolutely or strongly conserved amino acid positions (Trp15, Gln20, Leu42, Cys64, and Cys120). We have tested the role of these signature amino acids by mutational or chemical alteration of the ABA-1 protein of Ascaris, and examined the resulting modified proteins for perturbations of their lipid binding activities and structural integrity. Substitution of Trp15 and Gln20 both affect the stability of the protein in terms of resistance to thermal or chemical denaturation, but the ligand binding function is unaffected. Mutation of Leu42, however, disrupts both the protein's structural stability and functional integrity, as does chemical disruption of the disulfide bridge formed between Cys64 and Cys120. We also find that the C-terminal, but not the N-terminal, half of the protein binds fatty acids, indicating that the binding site may be confined to this part of the protein. This also supports the idea that the NPA units are themselves derived from an ancient duplication event, and that they may comprise two functionally distinct domains.

Biochemical and X-ray crystallographic studies on shikimate kinase: the important structural role of the P-loop lysine

Shikimate kinase, despite low sequence identity, has been shown to be structurally a member of the nucleoside monophosphate (NMP) kinase family, which includes adenylate kinase. In this paper we have explored the roles of residues in the P-loop of shikimate kinase, which forms the binding site for nucleotides and is one of the most conserved structural features in proteins. In common with many members of the P-loop family, shikimate kinase contains a cysteine residue 2 amino acids upstream of the essential lysine residue; the side chains of these residues are shown to form an ion pair. The C13S mutant of shikimate kinase was found to be enzymatically active, whereas the K15M mutant was inactive. However, the latter mutant had both increased thermostability and affinity for ATP when compared to the wild-type enzyme. The structure of the K15M mutant protein has been determined at 1.8 A, and shows that the organization of the P-loop and flanking regions is heavily disturbed. This indicates that, besides its role in catalysis, the P-loop lysine also has an important structural role. The structure of the K15M mutant also reveals that the formation of an additional arginine/aspartate ion pair is the most likely reason for its increased thermostability. From studies of ligand binding it appears that, like adenylate kinase, shikimate kinase binds substrates randomly and in a synergistic fashion, indicating that the two enzymes have similar catalytic mechanisms.

Human balancing of an inverted pendulum: is sway size controlled by ankle impedance?

Using the ankle musculature, subjects balanced a large inverted pendulum. The equilibrium of the pendulum is unstable and quasi-regular sway was observed like that in quiet standing. Two main questions were addressed. Can subjects systematically change sway size in response to instruction and availability of visual feedback? If so, do subjects decrease sway size by increasing ankle impedance or by some alternative mechanism? The position of the pendulum, the torque generated at each ankle and the soleus and tibialis anterior EMG were recorded. Results showed that subjects could significantly reduce the mean sway size of the pendulum by giving full attention to that goal. With visual feedback sway size could be minimised significantly more than without visual feedback. In changing sway size, the frequency of the sways was not changed. Results also revealed that ankle impedance and muscle co-contraction were not significantly changed when the sway size was decreased. As the ankle impedance and sway frequency do not change when the sway size is decreased, this implies no change in ankle stiffness or viscosity. Increasing ankle impedance, stiffness or viscosity are not the only methods by which sway size could be reduced. A reduction in torque noise or torque inaccuracy via a predictive process which provides active damping could reduce sway size without changing ankle impedance and is plausible given the data. Such a strategy involving motion recognition and generation of an accurate motor response may require higher levels of control than changing ankle impedance by altering reflex or feedforward gain.

Variations in disparate regions of the murine coronavirus spike protein impact the initiation of membrane fusion

The prototype JHM strain of murine hepatitis virus (MHV) is an enveloped, RNA-containing coronavirus that has been selected in vivo for extreme neurovirulence. This virus encodes spike (S) glycoproteins that are extraordinarily effective mediators of intercellular membrane fusion, unique in their ability to initiate fusion even without prior interaction with the primary MHV receptor, a murine carcinoembryonic antigen-related cell adhesion molecule (CEACAM). In considering the possible role of this hyperactive membrane fusion activity in neurovirulence, we discovered that the growth of JHM in tissue culture selected for variants that had lost murine CEACAM-independent fusion activity. Among the collection of variants, mutations were identified in regions encoding both the receptor-binding (S1) and fusion-inducing (S2) subunits of the spike protein. Each mutation was separately introduced into cDNA encoding the prototype JHM spike, and the set of cDNAs was expressed using vaccinia virus vectors. The variant spikes were similar to that of JHM in their assembly into oligomers, their proteolysis into S1 and S2 cleavage products, their transport to cell surfaces, and their affinity for a soluble form of murine CEACAM. However, these tissue culture-adapted spikes were significantly stabilized as S1-S2 heteromers, and their entirely CEACAM-dependent fusion activity was delayed or reduced relative to prototype JHM spikes. The mutations that we have identified therefore point to regions of the S protein that specifically regulate the membrane fusion reaction. We suggest that cultured cells, unlike certain in vivo environments, select for S proteins with delayed, CEACAM-dependent fusion activities that may increase the likelihood of virus internalization prior to the irreversible uncoating process.

The use of circular dichroism in the investigation of protein structure and function

Circular Dichroism (CD) relies on the differential absorption of left and right circularly polarised radiation by chromophores which either possess intrinsic chirality or are placed in chiral environments. Proteins possess a number of chromophores which can give rise to CD signals. In the far UV region (240-180 nm), which corresponds to peptide bond absorption, the CD spectrum can be analysed to give the content of regular secondary structural features such as alpha-helix and beta-sheet. The CD spectrum in the near UV region (320-260 nm) reflects the environments of the aromatic amino acid side chains and thus gives information about the tertiary structure of the protein. Other non-protein chromophores such as flavin and haem moieties can give rise to CD signals which depend on the precise environment of the chromophore concerned. Because of its relatively modest resource demands, CD has been used extensively to give useful information about protein structure, the extent and rate of structural changes and ligand binding. In the protein design field, CD is used to assess the structure and stability of the designed protein fragments. Studies of protein folding make extensive use of CD to examine the folding pathway; the technique has been especially important in characterising molten globule intermediates which may be involved in the folding process. CD is an extremely useful technique for assessing the structural integrity of membrane proteins during extraction and characterisation procedures. The interactions between chromophores can give rise to characteristic CD signals. This is well illustrated by the case of the light harvesting complex from photosynthetic bacteria, where the CD spectra can be analysed to indicate the extent of orbital overlap between the rings of bacteriochlorophyll molecules. It is therefore evident that CD is a versatile technique in structural biology, with an increasingly wide range of applications.

Probing the NADPH-binding site of Escherichia coli flavodoxin oxidoreductase

The structure of the Escherichia coli flavodoxin NADP(+) oxidoreductase (FLDR) places three arginines (R144, R174 and R184) in the proposed NADPH-binding site. Mutant enzymes produced by site-directed mutagenesis, in which each arginine was replaced by neutral alanine, were characterized. All mutants exhibited decreased NADPH-dependent cytochrome c reductase activity (R144A, 241.6 min(-1); R174A, 132.1 min(-1); R184A, 305.5 min(-1) versus wild type, 338.9 min(-1)) and increased K(m) for NADPH (R144A, 5.3 microM; R174A, 20.2 microM; R184A, 54.4 microM versus wild type, 3.9 microM). The k(cat) value for NADH-dependent cytochrome c reduction was increased for R174A (42.3 min(-1)) and R184A (50.4 min(-1)) compared with the wild type (33.0 min(-1)), consistent with roles for R174 and R184 in discriminating between NADPH/NADH by interaction with the adenosine ribose 2'-phosphate. Stopped-flow studies indicated that affinity (K(d)) for NADPH was markedly reduced in mutants R144A (635 microM) and R184A (2.3 mM) compared with the wild type (<5 microM). Mutant R184A displays the greatest change in pyridine nucleotide preference, with the NADH/NADPH K(d) ratio >175-fold lower than for wild-type FLDR. The rate constant for hydride transfer from NADPH to flavin was lowest for R174A (k(red)=8.82 s(-1) versus 22.63 s(-1) for the wild type), which also exhibited tertiary structure perturbation, as evidenced by alterations in CD and fluorescence spectra. Molecular modelling indicated that movement of the C-terminal tryptophan (W248) of FLDR is necessary to permit close approach of the nicotinamide ring of NADPH to the flavin. The positions of NADPH phosphates in the modelled structure are consistent with the kinetic data, with R174 and R184 located close to the adenosine ribose 2'-phosphate group, and R144 likely to interact with the nicotinamide ribose 5'-phosphate group.

Characterization of active-site mutants of Schizosaccharomyces pombe phosphoglycerate mutase. Elucidation of the roles of amino acids involved in substrate binding and catalysis

The roles of a number of amino acids present at the active site of the monomeric phosphoglycerate mutase from the fission yeast Schizosaccharomyces pombe have been explored by site-directed mutagenesis. The amino acids examined could be divided broadly into those presumed from previous related structural studies to be important in the catalytic process (R14, S62 and E93) and those thought to be important in substrate binding (R94, R120 and R121). Most of these residues have not previously been studied by site-directed mutagenesis. All the mutants except R14 were expressed in an engineered null strain of Saccharomyces cerevisiae (S150-gpm:HIS) in good yield. The R14Q mutant was expressed in good yield in the transformed AH22 strain of S. cerevisiae. The S62A mutant was markedly unstable, preventing purification. The various mutants were purified to homogeneity and characterized in terms of kinetic parameters, CD and fluorescence spectra, stability towards denaturation by guanidinium chloride, and stability of phosphorylated enzyme intermediate. In addition, the binding of substrate (3-phosphoglycerate) to wild-type, E93D and R120,121Q enzymes was measured by isothermal titration calorimetry. The results provide evidence for the proposed roles of each of these amino acids in the catalytic cycle and in substrate binding, and will support the current investigation of the structure and dynamics of the enzyme using multidimensional NMR techniques.