Conformational states of the microtubule nucleator, the γ-tubulin ring complex

Microtubules (MTs) perform essential functions in the cell, and it is critical that they are made at the correct cellular location and cell cycle stage. This nucleation process is catalyzed by the γ-tubulin ring complex (γ-TuRC), a cone-shaped protein complex composed of over 30 subunits. Despite recent insight into the structure of vertebrate γ-TuRC, which shows that its diameter is wider than that of a MT, and that it exhibits little of the symmetry expected for an ideal MT template, the question of how γ-TuRC achieves MT nucleation remains open. Here, we utilized single particle cryo-EM to identify two conformations of γ-TuRC. The helix composed of 14 γ-tubulins at the top of the γ-TuRC cone undergoes substantial deformation, which is predominantly driven by bending of the hinge between the GRIP1 and GRIP2 domains of the γ-tubulin complex proteins. However, surprisingly, this deformation does not remove the inherent asymmetry of γ-TuRC. To further investigate the role of γ-TuRC conformational change, we used cryo electron-tomography (cryo-ET) to obtain a 3D reconstruction of γ-TuRC bound to a nucleated MT, providing insight into the post-nucleation state. Rigid-body fitting of our cryo-EM structures into this reconstruction suggests that the MT lattice is nucleated by spokes 2 through 14 of the γ-tubulin helix, which entails spokes 13 and 14 becoming more structured than what is observed in apo γ-TuRC. Together, our results allow us to propose a model for conformational changes in γ-TuRC and how these may facilitate MT formation in a cell.

Integrated model of the vertebrate augmin complex

Accurate segregation of chromosomes is required to maintain genome integrity during cell division. This feat is accomplished by the microtubule-based spindle. To build a spindle rapidly and with high fidelity, cells take advantage of branching microtubule nucleation, which rapidly amplifies microtubules during cell division. Branching microtubule nucleation relies on the hetero-octameric augmin complex, but lack of structure information about augmin has hindered understanding how it promotes branching. In this work, we combine cryo-electron microscopy, protein structural prediction, and visualization of fused bulky tags via negative stain electron microscopy to identify the location and orientation of each subunit within the augmin structure. Evolutionary analysis shows that augmin's structure is highly conserved across eukaryotes, and that augmin contains a previously unidentified microtubule binding site. Thus, our findings provide insight into the mechanism of branching microtubule nucleation.

The conserved centrosomin motif, γTuNA, forms a dimer that directly activates microtubule nucleation by the γ-tubulin ring complex (γTuRC)

To establish the microtubule cytoskeleton, the cell must tightly regulate when and where microtubules are nucleated. This regulation involves controlling the initial nucleation template, the γ-tubulin ring complex (γTuRC). Although γTuRC is present throughout the cytoplasm, its activity is restricted to specific sites including the centrosome and Golgi. The well-conserved γ-tubulin nucleation activator (γTuNA) domain has been reported to increase the number of microtubules (MTs) generated by γTuRCs. However, previously we and others observed that γTuNA had a minimal effect on the activity of antibody-purified Xenopus γTuRCs in vitro (Thawani et al., eLife, 2020; Liu et al., 2020). Here, we instead report, based on improved versions of γTuRC, γTuNA, and our TIRF assay, the first real-time observation that γTuNA directly increases γTuRC activity in vitro, which is thus a bona fide γTuRC activator. We further validate this effect in Xenopus egg extract. Via mutation analysis, we find that γTuNA is an obligate dimer. Moreover, efficient dimerization as well as γTuNA's L70, F75, and L77 residues are required for binding to and activation of γTuRC. Finally, we find that γTuNA's activating effect opposes inhibitory regulation by stathmin. In sum, our improved assays prove that direct γTuNA binding strongly activates γTuRCs, explaining previously observed effects of γTuNA expression in cells and illuminating how γTuRC-mediated microtubule nucleation is regulated.

How Microtubules Build the Spindle Branch by Branch

The microtubule (MT) cytoskeleton provides the architecture that governs intracellular organization and the regulated motion of macromolecules through the crowded cytoplasm. The key to establishing a functioning cytoskeletal architecture is regulating when and where new MTs are nucleated. Within the spindle, the vast majority of MTs are generated through a pathway known as branching MT nucleation, which exponentially amplifies MT number in a polar manner. Whereas other MT nucleation pathways generally require a complex organelle such as the centrosome or Golgi apparatus to localize nucleation factors, the branching site is based solely on a simple, preformed MT, making it an ideal system to study MT nucleation. In this review, we address recent developments in characterizing branching factors, the branching reaction, and its regulation, as well as branching MT nucleation in systems beyond the spindle and within human disease. Expected final online publication date for the Annual Review of Cell and Developmental Biology Volume 38 is October 2022. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

Biophysical Characterization of Cancer-Related Carbonic Anhydrase IX

Upregulation of carbonic anhydrase IX (CA IX) is associated with several aggressive forms of cancer and promotes metastasis. CA IX is normally constitutively expressed at low levels in selective tissues associated with the gastrointestinal tract, but is significantly upregulated upon hypoxia in cancer. CA IX is a multi-domain protein, consisting of a cytoplasmic region, a single-spanning transmembrane helix, an extracellular CA catalytic domain, and a proteoglycan-like (PG) domain. Considering the important role of CA IX in cancer progression and the presence of the unique PG domain, little information about the PG domain is known. Here, we report biophysical characterization studies to further our knowledge of CA IX. We report the 1.5 Å resolution crystal structure of the wild-type catalytic domain of CA IX as well as small angle X-ray scattering and mass spectrometry of the entire extracellular region. We used matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrometry to characterize the spontaneous degradation of the CA IX PG domain and confirm that it is only the CA IX catalytic domain that forms crystals. Small angle X-ray scattering analysis of the intact protein indicates that the PG domain is not randomly distributed and adopts a compact distribution of shapes in solution. The observed dynamics of the extracellular domain of CA IX could have physiological relevance, including observed cleavage and shedding of the PG domain.

Structural comparison of protiated, H/D-exchanged and deuterated human carbonic anhydrase IX

In this work, the X-ray crystal structures of four different deuterium-labelled versions of a surface variant of human carbonic anhydrase IX are compared and discussed. The results show that the overall structure and active-site organization of each version are essentially the same, paving the way for future neutron protein crystallography studies.

Human carbonic anhydrase IX (CA IX) expression is upregulated in hypoxic solid tumours, promoting cell survival and metastasis. This observation has made CA IX a target for the development of CA isoform-selective inhibitors. To enable structural studies of CA IX–inhibitor complexes using X-ray and neutron crystallography, a CA IX surface variant (CA IX_SV; the catalytic domain with six surface amino-acid substitutions) has been developed that can be routinely crystallized. Here, the preparation of protiated (H/H), H/D-exchanged (H/D) and deuterated (D/D) CA IX_SV for crystallographic studies and their structural comparison are described. Four CA IX_SV X-ray crystal structures are compared: two H/H crystal forms, an H/D crystal form and a D/D crystal form. The overall active-site organization in each version is essentially the same, with only minor positional changes in active-site solvent, which may be owing to deuteration and/or resolution differences. Analysis of the crystal contacts and packing reveals different arrangements of CA IX_SV compared with previous reports. To our knowledge, this is the first report comparing three different deuterium-labelled crystal structures of the same protein, marking an important step in validating the active-site structure of CA IX_SV for neutron protein crystallography.

Carbonic anhydrase II microcrystals suitable for XFEL studies

Recent advances in X-ray free-electron laser (XFEL) sources have permitted the study of protein dynamics. Femtosecond X-ray pulses have allowed the visualization of intermediate states in enzyme catalysis. In this study, the growth of carbonic anhydrase II microcrystals (40-80 µm in length) suitable for the collection of XFEL diffraction data at the Pohang Accelerator Laboratory is demonstrated. The crystals diffracted to 1.7 Å resolution and were indexed in space group P21, with unit-cell parameters a = 42.2, b = 41.2, c = 72.0 Å, β = 104.2°. These preliminary results provide the necessary framework for time-resolved experiments to study carbonic anhydrase catalysis at XFEL beamlines.

Carbonic Anhydrases: Role in pH Control and Cancer

The pH of the tumor microenvironment drives the metastatic phenotype and chemotherapeutic resistance of tumors. Understanding the mechanisms underlying this pH-dependent phenomenon will lead to improved drug delivery and allow the identification of new therapeutic targets. This includes an understanding of the role pH plays in primary tumor cells, and the regulatory factors that permit cancer cells to thrive. Over the last decade, carbonic anhydrases (CAs) have been shown to be important mediators of tumor cell pH by modulating the bicarbonate and proton concentrations for cell survival and proliferation. This has prompted an effort to inhibit specific CA isoforms, as an anti-cancer therapeutic strategy. Of the 12 active CA isoforms, two, CA IX and XII, have been considered anti-cancer targets. However, other CA isoforms also show similar activity and tissue distribution in cancers and have not been considered as therapeutic targets for cancer treatment. In this review, we consider all the CA isoforms and their possible role in tumors and their potential as targets for cancer therapy.

Crystal Structure of Cleaved Serp-1, a Myxomavirus-Derived Immune Modulating Serpin: Structural Design of Serpin Reactive Center Loop Peptides with Improved Therapeutic Function

The Myxomavirus-derived protein Serp-1 has potent anti-inflammatory activity in models of vasculitis, lupus, viral sepsis, and transplant. Serp-1 has also been tested successfully in a Phase IIa clinical trial in unstable angina, representing a "first-in-class" therapeutic. Recently, peptides derived from the reactive center loop (RCL) have been developed as stand-alone therapeutics for reducing vasculitis and improving survival in MHV68-infected mice. However, both Serp-1 and the RCL peptides lose activity in MHV68-infected mice after antibiotic suppression of intestinal microbiota. Here, we utilize a structure-guided approach to design and test a series of next-generation RCL peptides with improved therapeutic potential that is not reduced when the peptides are combined with antibiotic treatments. The crystal structure of cleaved Serp-1 was determined to 2.5 Å resolution and reveals a classical serpin structure with potential for serpin-derived RCL peptides to bind and inhibit mammalian serpins, plasminogen activator inhibitor 1 (PAI-1), anti-thrombin III (ATIII), and α-1 antitrypsin (A1AT), and target proteases. Using in silico modeling of the Serp-1 RCL peptide, S-7, we designed several modified RCL peptides that were predicted to have stronger interactions with human serpins because of the larger number of stabilizing hydrogen bonds. Two of these peptides (MPS7-8 and -9) displayed extended activity, improving survival where activity was previously lost in antibiotic-treated MHV68-infected mice (P < 0.0001). Mass spectrometry and kinetic assays suggest interaction of the peptides with ATIII, A1AT, and target proteases in mouse and human plasma. In summary, we present the next step toward the development of a promising new class of anti-inflammatory serpin-based therapeutics.

Active-site solvent replenishment observed during human carbonic anhydrase II catalysis

Human carbonic anhydrase II (hCA II) is a zinc metalloenzyme that catalyzes the reversible hydration/dehydration of CO2/HCO3-. Although hCA II has been extensively studied to investigate the proton-transfer process that occurs in the active site, its underlying mechanism is still not fully understood. Here, ultrahigh-resolution crystallographic structures of hCA II cryocooled under CO2 pressures of 7.0 and 2.5 atm are presented. The structures reveal new intermediate solvent states of hCA II that provide crystallographic snapshots during the restoration of the proton-transfer water network in the active site. Specifically, a new intermediate water (WI') is observed next to the previously observed intermediate water WI, and they are both stabilized by the five water molecules at the entrance to the active site (the entrance conduit). Based on these structures, a water network-restructuring mechanism is proposed, which takes place at the active site after the nucleophilic attack of OH- on CO2. This mechanism explains how the zinc-bound water (WZn) and W1 are replenished, which are directly responsible for the reconnection of the His64-mediated proton-transfer water network. This study provides the first 'physical' glimpse of how a water reservoir flows into the hCA II active site during its catalytic activity.

Exploring Heteroaryl-pyrazole Carboxylic Acids as Human Carbonic Anhydrase XII Inhibitors

We report the synthesis, biological evaluation, and structural study of a series of substituted heteroaryl-pyrazole carboxylic acid derivatives. These compounds have been developed as inhibitors of specific isoforms of carbonic anhydrase (CA), with potential as prototypes of a new class of chemotherapeutics. Both X-ray crystallography and computational modeling provide insights into the CA inhibition mechanism. Results indicate that this chemotype produces an indirect interference with the zinc ion, thus behaving differently from other related nonclassical inhibitors. Among the tested compounds, 2c with K_i = 0.21 μM toward hCA XII demonstrated significant antiproliferative activity against hypoxic tumor cell lines. Taken together, the results thus provide the basis of structural determinants for the development of novel anticancer agents.

Abstract 2931: Targeting membrane-bound carbonic anhydrases in breast cancer to intervene in the metastatic phenotype

Breast cancer is the second leading cause of cancer related deaths among women in the United States. Despite the tremendous progress that has been made towards treating localized tumors, nearly 40,000 women die each year, predominantly from metastatic drug resistance. The tumor microenvironment plays a pivotal role in determining tumor growth, invasion, metastasis, and therapeutic success or failure. Therefore, a therapy targeting the tumor microenvironment is needed to sufficiently preserve the quality of life of cancer patients, by inhibiting metastasis. Elevated levels of Carbonic anhydrase IX (CAIX) expression in primary breast cancers is a marker for highly aggressive and metastatic tumors, especially of the triple negative subtype (TNBC). It is also associated with hypoxia, extracellular acidification, and poor prognosis. Low pH (values of ~6.5-6.8) is toxic to normal cells in the tumor microenvironment while enhancing cancer cell proliferation and tumor growth. Our goal was to compare the structure of a CAIX-mimic bound to ureidosulfonamide inhibitors with the biological activity of these inhibitors in triple negative and estrogen receptor positive (ER+) breast cancer cell lines. CAIX is a reversible enzyme and at low pH (high proton concentration), the enzyme will consume protons, raising pH. Our hypothesis is that CAIX inhibition, in the context of an acidic microenvironment, will dysregulate its ability to maintain the acidic pH preferred by cancer cells which favors their growth and migration. In this study, we have shown the interaction of sulfonamide-based inhibitors with a CAIX-mimic using X-ray crystallography. These structures show that the inhibitors make multiple contacts within the active site cavity. This is consistent with the inhibitor-induced decrease in CAIX activity and to some extent expression. We have also investigated the effect of CA inhibition on breast cancer cell growth, proliferation, activation of cell death pathways and migration. This reveals that, although CA inhibition with the sulfonamide-based compounds inhibits cell growth and migration, it does not activate apoptotic pathways. In total, these observations indicate that CAIX is a viable small molecular drug target for the treatment of metastatic breast cancer.

Citation Format: Mam Y. Mboge, Zhijuan Chen, Brian P. Mahon, Chingkkuang Tu, Alyssa S. Wolff, John V. Mathias, Fabrizio Carta, Claudiu T. Supuran, Rob McKenna, Susan C. Frost. Targeting membrane-bound carbonic anhydrases in breast cancer to intervene in the metastatic phenotype [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 2931. doi:10.1158/1538-7445.AM2017-2931

Structure activity study of carbonic anhydrase IX: Selective inhibition with ureido-substituted benzenesulfonamides

Ureido-substituted benzenesulfonamides (USBs) show great promise as selective and potent inhibitors for human carbonic anhydrase hCA IX and XII, with one such compound (SLC-0111/U-F) currently in clinical trials (clinical trials.gov, NCT02215850). In this study, the crystal structures of both hCA II (off-target) and an hCA IX-mimic (target) in complex with selected USBs (U-CH3, U-F, and U-NO2), at resolutions of 1.9 Å or better, are presented, and demonstrate differences in the binding modes within the two isoforms. The presence of residue Phe 131 in hCA II causes steric hindrance (U-CH3, 1765 nM; U-F, 960 nM; U-NO2, 15 nM) whereas in hCA IX (U-CH3, 7 nM; U-F, 45 nM; U-NO2, 1 nM) and hCA XII (U-CH3, 6 nM; U-F, 4 nM; U-NO2, 6 nM), 131 is a Val and Ala, respectively, allows for more favorable binding. Our results provide insight into the mechanism of USB selective inhibition and useful information for structural design and drug development, including synthesis of hybrid USB compounds with improved physiochemical properties.

The influence of macrophages on mesenchymal stromal cell therapy: passive or aggressive agents?

Mesenchymal stromal cells (MSC) have emerged as promising cell therapies for multiple conditions based on demonstrations of their potent immunomodulatory and regenerative capacities in models of inflammatory disease. Understanding the effects of MSC on T cells has dominated the majority of work carried out in this field to date; recently, however, a number of studies have shown that the therapeutic effect of MSC requires the presence of macrophages. It is timely to review the mechanisms and manner by which MSC modulate macrophage populations in order to design more effective MSC therapies and clinical studies. A complex cross-talk exists through which MSC and macrophages communicate, a communication that is not controlled exclusively by MSC. Here, we examine the evidence that suggests that MSC not only respond to inflammatory macrophages and adjust their secretome accordingly, but also that macrophages respond to encounters with MSC, creating a feedback loop which contributes to the immune regulation observed following MSC therapy. Future studies examining the effects of MSC on macrophages should consider the antagonistic role that macrophages play in this exchange.

Structure-Activity Relationships of Benzenesulfonamide-Based Inhibitors towards Carbonic Anhydrase Isoform Specificity

Carbonic anhydrases (CAs) are implicated in a wide range of diseases, including the upregulation of isoforms CA IX and XII in many aggressive cancers. However, effective inhibition of disease-implicated CAs should minimally affect the ubiquitously expressed isoforms, including CA I and II, to improve directed distribution of the inhibitors to the cancer-associated isoforms and reduce side effects. Four benzenesulfonamide-based inhibitors were synthesized by using the tail approach and displayed nanomolar affinities for several CA isoforms. The crystal structures of the inhibitors bound to a CA IX mimic and CA II are presented. Further in silico modeling was performed with the inhibitors docked into CA I and XII to identify residues that contributed to or hindered their binding interactions. These structural studies demonstrated that active-site residues lining the hydrophobic pocket, especially positions 92 and 131, dictate the positional binding and affinity of inhibitors, whereas the tail groups modulate CA isoform specificity. Geometry optimizations were performed on each ligand in the crystal structures and showed that the energetic penalties of the inhibitor conformations were negligible compared to the gains from active-site interactions. These studies further our understanding of obtaining isoform specificity when designing small molecule CA inhibitors.

Effects of Hinge-region Natural Polymorphisms on Human Immunodeficiency Virus-Type 1 Protease Structure, Dynamics, and Drug Pressure Evolution

Multidrug resistance to current Food and Drug Administration-approved HIV-1 protease (PR) inhibitors drives the need to understand the fundamental mechanisms of how drug pressure-selected mutations, which are oftentimes natural polymorphisms, elicit their effect on enzyme function and resistance. Here, the impacts of the hinge-region natural polymorphism at residue 35, glutamate to aspartate (E35D), alone and in conjunction with residue 57, arginine to lysine (R57K), are characterized with the goal of understanding how altered salt bridge interactions between the hinge and flap regions are associated with changes in structure, motional dynamics, conformational sampling, kinetic parameters, and inhibitor affinity. The combined results reveal that the single E35D substitution leads to diminished salt bridge interactions between residues 35 and 57 and gives rise to the stabilization of open-like conformational states with overall increased backbone dynamics. In HIV-1 PR constructs where sites 35 and 57 are both mutated (e.g. E35D and R57K), x-ray structures reveal an altered network of interactions that replace the salt bridge thus stabilizing the structural integrity between the flap and hinge regions. Despite the altered conformational sampling and dynamics when the salt bridge is disrupted, enzyme kinetic parameters and inhibition constants are similar to those obtained for subtype B PR. Results demonstrate that these hinge-region natural polymorphisms, which may arise as drug pressure secondary mutations, alter protein dynamics and the conformational landscape, which are important thermodynamic parameters to consider for development of inhibitors that target for non-subtype B PR.

The Structure of Carbonic Anhydrase IX Is Adapted for Low-pH Catalysis

Human carbonic anhydrase IX (hCA IX) expression in many cancers is associated with hypoxic tumors and poor patient outcome. Inhibitors of hCA IX have been used as anticancer agents with some entering Phase I clinical trials. hCA IX is transmembrane protein whose catalytic domain faces the extracellular tumor milieu, which is typically associated with an acidic microenvironment. Here, we show that the catalytic domain of hCA IX (hCA IX-c) exhibits the necessary biochemical and biophysical properties that allow for low pH stability and activity. Furthermore, the unfolding process of hCA IX-c appears to be reversible, and its catalytic efficiency is thought to be correlated directly with its stability between pH 3.0 and 8.0 but not above pH 8.0. To rationalize this, we determined the X-ray crystal structure of hCA IX-c to 1.6 Å resolution. Insights from this study suggest an understanding of hCA IX-c stability and activity in low-pH tumor microenvironments and may be applicable to determining pH-related effects on enzymes.

Abstract B25: Characterization, targeting, and modulation of carbonic anhydrase IX activity for the development of small-molecule inhibitors to treat triple-negative breast cancer

The microenvironment within a solid tumor is usually heterogeneous with certain regions being acidic and hypoxic. These acidic and hypoxic regions arise from rapidly proliferating cells combined with poor tumor perfusion. Cancer cells cope with these hostile changes in their microenvironment by expressing genes that are essential for survival. One of the coping mechanisms is an upregulation of pH regulatory factors, including carbonic anhydrase IX (CAIX). The action of CAIX helps to maintain physiological pH inside the cell (pHi) while regulating extracellular acidification (pHe). Extracellular acidification of the tumor microenvironment promotes local invasion, metastasis and decreases the effectiveness of adjuvant therapies, thus contributing to poor clinical outcome. Our goal was to compare the structure of a CAIX-mimic bound to ureidosulfonamide inhibitors with the biological activity of these inhibitors in a triple negative breast cancer cell line. CAIX is a reversible enzyme and at low pH (high proton concentration), the enzyme will consume protons, raising pH. Our hypothesis is that CAIX inhibition, in the context of an acidic microenvironment, will dysregulate its ability to maintain the acidic pH preferred by cancer cells which favors their growth and migration. In this study, we have shown the interaction of sulfonamide-based inhibitors using X-ray crystallography methods. These structures show the inhibitors make multiple contacts within the active site cavity. This is consistent with the inhibitor-induced decrease in CAIX activity measured as 18O exchange between H2O16 and H13C18O3 . We have also investigated the effect CAIX inhibition on cancer cell metabolism and extracellular acidification using Seahorse technology. This reveals that CAIX may contribute to the “non-glycolytic” acidification process. In total, these observations indicate that CAIX is a viable small molecular drug target and contribute to our understanding of the function of CAIX in modulating pH in cancer cells.

Citation Format: Mam Y. Mboge, Zhijuan Chen, Brian P. Mahon, Nicole Lamas, Shingkuang Tu, Fabrizio Carta, Claudiu T. Superan, Robert McKenna, Susan C. Frost. Characterization, targeting, and modulation of carbonic anhydrase IX activity for the development of small-molecule inhibitors to treat triple-negative breast cancer. [abstract]. In: Proceedings of the AACR Special Conference: Function of Tumor Microenvironment in Cancer Progression; 2016 Jan 7–10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2016;76(15 Suppl):Abstract nr B25.

Kinetic and X-ray crystallographic investigations on carbonic anhydrase isoforms I, II, IX and XII of a thioureido analog of SLC-0111

SLC-0111 (4-(4-fluorophenylureido)-benzenesulfonamide) is the first carbonic anhydrase (CA, EC 4.2.1.1) IX inhibitor to reach phase I clinical trials as an antitumor/antimetastatic agent. Here we report a kinetic and X-ray crystallographic study of a congener of SLC-0111 which incorporates a thioureido instead of ureido linker between the two aromatic rings as inhibitor of four physiologically relevant CA isoforms. Similar to SLC-0111, the thioureido derivative was a weak hCA I and II inhibitor and a potent one against hCA IX and XII. X-ray crystallography of its adduct with hCA II and comparison of the structure with that of other five hCA II-sulfonamide adducts belonging to the SLC-0111 series, afforded us to understand the particular inhibition profile of the new sulfonamide. Similar to SLC-0111, the thioureido sulfonamide primarily interacted with the hydrophobic side of the hCA II active site, with the tail participating in van der Waals interactions with Phe131 and Pro202, in addition to the coordination of the deprotonated sulfonamide to the active site metal ion. On the contrary, the tail of other sulfonamides belonging to the SLC-0111 series (2-isopropyl-phenyl; 3-nitrophenyl) were orientated towards the hydrophilic half of the active site, which was correlated with orders of magnitude better inhibitory activity against hCA II, and a loss of selectivity for the inhibition of the tumor-associated CAs.

Sulfonamide inhibition studies of the α-carbonic anhydrase from the gammaproteobacterium Thiomicrospira crunogena XCL-2, TcruCA

We report a sulfonamide/sulfamate inhibition study of the α-carbonic anhydrase (CA, EC 4.2.1.1) present in the gammaproteobacterium Thiomicrospira crunogena XCL-2, a mesophilic hydrothermal vent-isolate organism, TcruCA. As Thiomicrospira crunogena is one of thousands of marine organisms that uses CA for metabolic regulation, the effect of sulfonamide inhibition has been considered. Sulfonamide-based drugs have been widely used in a variety of antibiotics, and bioelimination of these compounds results in exposure of these compounds to marine life. The enzyme was highly inhibited, with Ki values ranging from 2.5 to 40.7nM by a variety of sulfonamides including acetazolamide, methazolamide, ethoxzolamide, dichlorophenamide, dorzolamide, brinzolamide, benzolamide and benzenesulfonamides incorporating 4-hydroxyalkyl moieties. Less effective inhibitors were topiramate, zonisamide, celecoxib, saccharin and hydrochlorothiazide as well as simple benzenesulfonamides incorporating amino, halogeno, alkyl, aminoalkyl and other moieties in the ortho- or para-positions of the aromatic ring (Kis of 202-933nM). The active site interactions between TcruCA and three clinically-used CA inhibitors, acetazolamide (Diamox®), dorzolamide (Trusopt®), and brinzolamide (Azopt®) are studied using molecular docking to provide insight into the reported Ki values. Comparison between various enzymes belonging to this family may also bring interesting hints in these fascinating phenomena.

Activity and anion inhibition studies of the α-carbonic anhydrase from Thiomicrospira crunogena XCL-2 Gammaproteobacterium

Thiomicrospira crunogena XCL-2 expresses an α-carbonic anhydrase (TcruCA). Sequence alignments reveal that TcruCA displays a high sequence identity (>30%) relative to other α-CAs. This includes three conserved histidines that coordinate the active site zinc, a histidine proton shuttling residue, and opposing hydrophilic and hydrophobic sides that line the active site. The catalytic efficiency of TcruCA is considered moderate relative to other α-CAs (k(cat)/K(M)=1.1×10(7) M(-1) s(-1)), being a factor of ten less efficient than the most active α-CAs. TcruCA is also inhibited by anions with Cl(-), Br(-), and I(-), all showing Ki values in the millimolar range (53-361 mM). Hydrogen sulfide (HS(-)) revealed the highest affinity for TcruCA with a Ki of 1.1 μM. It is predicted that inhibition of TcruCA by HS(-) (an anion commonly found in the environment where Thiomicrospira crunogena is located) is a way for Thiomicrospira crunogena to regulate its carbon-concentrating mechanism (CCM) and thus the organism's metabolic functions. Results from this study provide preliminary insights into the role of TcruCA in the general metabolism of Thiomicrospira crunogena.

A sucrose-binding site provides a lead towards an isoform-specific inhibitor of the cancer-associated enzyme carbonic anhydrase IX

Human carbonic anhydrase (CA; EC 4.2.1.1) isoform IX (CA IX) is an extracellular zinc metalloenzyme that catalyzes the reversible hydration of CO2 to HCO3(-), thereby playing a role in pH regulation. The majority of normal functioning cells exhibit low-level expression of CA IX. However, in cancer cells CA IX is upregulated as a consequence of a metabolic transition known as the Warburg effect. The upregulation of CA IX for cancer progression has drawn interest in it being a potential therapeutic target. CA IX is a transmembrane protein, and its purification, yield and crystallization have proven challenging to structure-based drug design, whereas the closely related cytosolic soluble isoform CA II can be expressed and crystallized with ease. Therefore, we have utilized structural alignments and site-directed mutagenesis to engineer a CA II that mimics the active site of CA IX. In this paper, the X-ray crystal structure of this CA IX mimic in complex with sucrose is presented and has been refined to a resolution of 1.5 Å, an Rcryst of 18.0% and an Rfree of 21.2%. The binding of sucrose at the entrance to the active site of the CA IX mimic, and not CA II, in a non-inhibitory mechanism provides a novel carbohydrate moiety binding site that could be further exploited to design isoform-specific inhibitors of CA IX.

Observed surface lysine acetylation of human carbonic anhydrase II expressed in Escherichia coli

Acetylation of surface lysine residues of proteins has been observed in Escherichia coli (E. coli), an organism that has been extensively utilized for recombinant protein expression. This post-translational modification is shown to be important in various processes such as metabolism, stress-response, transcription, and translation. As such, utilization of E. coli expression systems for protein production may yield non-native acetylation events of surface lysine residues. Here we present the crystal structures of wild-type and a variant of human carbonic anhydrase II (hCA II) that have been expressed in E. coli and exhibit surface lysine acetylation and we speculate on the effect this has on the conformational stability of each enzyme. Both structures were determined to 1.6 Å resolution and show clear electron density for lysine acetylation. The lysine acetylation does not distort the structure and the surface lysine acetylation events most likely do not interfere with the biological interpretation. However, there is a reduction in conformational stability in the hCA II variant compared to wild type (∼ 4°C decrease). This may be due to other lysine acetylation events that have occurred but are not visible in the crystal structure due to intrinsic disorder. Therefore, surface lysine acetylation events may affect overall protein stability and crystallization, and should be considered when using E. coli expression systems.

Structural and biophysical characterization of the α-carbonic anhydrase from the gammaproteobacterium Thiomicrospira crunogena XCL-2: insights into engineering thermostable enzymes for CO2 sequestration

Biocatalytic CO2 sequestration to reduce greenhouse-gas emissions from industrial processes is an active area of research. Carbonic anhydrases (CAs) are attractive enzymes for this process. However, the most active CAs display limited thermal and pH stability, making them less than ideal. As a result, there is an ongoing effort to engineer and/or find a thermostable CA to fulfill these needs. Here, the kinetic and thermal characterization is presented of an α-CA recently discovered in the mesophilic hydrothermal vent-isolate extremophile Thiomicrospira crunogena XCL-2 (TcruCA), which has a significantly higher thermostability compared with human CA II (melting temperature of 71.9°C versus 59.5°C, respectively) but with a tenfold decrease in the catalytic efficiency. The X-ray crystallographic structure of the dimeric TcruCA shows that it has a highly conserved yet compact structure compared with other α-CAs. In addition, TcruCA contains an intramolecular disulfide bond that stabilizes the enzyme. These features are thought to contribute significantly to the thermostability and pH stability of the enzyme and may be exploited to engineer α-CAs for applications in industrial CO2 sequestration.

Saccharin: a lead compound for structure-based drug design of carbonic anhydrase IX inhibitors

Carbonic anhydrase IX (CA IX) is a key modulator of aggressive tumor behavior and a prognostic marker and target for several cancers. Saccharin (SAC) based compounds may provide an avenue to overcome CA isoform specificity, as they display both nanomolar affinity and preferential binding, for CA IX compared to CA II (>50-fold for SAC and >1000-fold when SAC is conjugated to a carbohydrate moiety). The X-ray crystal structures of SAC and a SAC-carbohydrate conjugate bound to a CA IX-mimic are presented and compared to CA II. The structures provide substantial new insight into the mechanism of SAC selective CA isoform inhibition.

Targeting carbonic anhydrase IX activity and expression

Metastatic tumors are often hypoxic exhibiting a decrease in extracellular pH (~6.5) due to a metabolic transition described by the Warburg Effect. This shift in tumor cell metabolism alters the tumor milieu inducing tumor cell proliferation, angiogenesis, cell motility, invasiveness, and often resistance to common anti-cancer treatments; hence hindering treatment of aggressive cancers. As a result, tumors exhibiting this phenotype are directly associated with poor prognosis and decreased survival rates in cancer patients. A key component to this tumor microenvironment is carbonic anhydrase IX (CA IX). Knockdown of CA IX expression or inhibition of its activity has been shown to reduce primary tumor growth, tumor proliferation, and also decrease tumor resistance to conventional anti-cancer therapies. As such several approaches have been taken to target CA IX in tumors via small-molecule, anti-body, and RNAi delivery systems. Here we will review recent developments that have exploited these approaches and provide our thoughts for future directions of CA IX targeting for the treatment of cancer.

Defective hydrophobic sliding mechanism and active site expansion in HIV-1 protease drug resistant variant Gly48Thr/Leu89Met: mechanisms for the loss of saquinavir binding potency

HIV drug resistance continues to emerge; consequently, there is an urgent need to develop next generation antiretroviral therapeutics.1 Here we report on the structural and kinetic effects of an HIV protease drug resistant variant with the double mutations Gly48Thr and Leu89Met (PR_G48T/L89M), without the stabilizing mutations Gln7Lys, Leu33Ile, and Leu63Ile. Kinetic analyses reveal that PR_G48T/L89M and PR_WT share nearly identical Michaelis–Menten parameters; however, PR_G48T/L89M exhibits weaker binding for IDV (41-fold), SQV (18-fold), APV (15-fold), and NFV (9-fold) relative to PR_WT. A 1.9 Å resolution crystal structure was solved for PR_G48T/L89M bound with saquinavir (PR_{G48T/L89M-SQV}) and compared to the crystal structure of PR_WT bound with saquinavir (PR_WT-SQV). PR_{G48T/L89M-SQV} has an enlarged active site resulting in the loss of a hydrogen bond in the S3 subsite from Gly48 to P3 of SQV, as well as less favorable hydrophobic packing interactions between P1 Phe of SQV and the S1 subsite. PR_{G48T/L89M-SQV} assumes a more open conformation relative to PR_WT-SQV, as illustrated by the downward displacement of the fulcrum and elbows and weaker interatomic flap interactions. We also show that the Leu89Met mutation disrupts the hydrophobic sliding mechanism by causing a redistribution of van der Waals interactions in the hydrophobic core in PR_{G48T/L89M-SQV}. Our mechanism for PR_{G48T/L89M-SQV} drug resistance proposes that a defective hydrophobic sliding mechanism results in modified conformational dynamics of the protease. As a consequence, the protease is unable to achieve a fully closed conformation that results in an expanded active site and weaker inhibitor binding.

Structural insights into carbonic anhydrase IX isoform specificity of carbohydrate-based sulfamates

Carbonic anhydrase IX (CA IX) is an extracellular transmembrane homodimeric zinc metalloenzyme that has been validated as a prognostic marker and therapeutic target for several types of aggressive cancers. CA IX shares a close homology with other CA isoforms, making the design of CA IX isoform selective inhibitors challenging. In this paper, we describe the development of a new class of CA IX inhibitors that comprise a sulfamate as the zinc binding group, a variable linker, and a carbohydrate “tail” moiety. Seven compounds inhibited CA IX with low nM K_i values of 1–2 nM and also exhibited permeability profiles to preferentially target the binding of extracellular CA IX over cytosolic CAs. The crystal structures of two of these compounds in complex with a CA IX-mimic (a variant of CA II, with active site residues that mimic CA IX) and one compound in complex with CA II have been determined to 1.7 Å resolution or better and demonstrate a selective mechanism of binding between the hydrophilic and hydrophobic pockets of CA IX versus CA II. These compounds present promising candidates for anti-CA IX drugs and the treatment for several aggressive cancer types.

Human mesenchymal stem cells suppress donor CD4(+) T cell proliferation and reduce pathology in a humanized mouse model of acute graft-versus-host disease

Acute graft-versus-host disease (aGVHD) is a life-threatening complication following allogeneic haematopoietic stem cell transplantation (HSCT), occurring in up to 30-50% of patients who receive human leucocyte antigen (HLA)-matched sibling transplants. Current therapies for steroid refractory aGVHD are limited, with the prognosis of patients suboptimal. Mesenchymal stem or stromal cells (MSC), a heterogeneous cell population present in many tissues, display potent immunomodulatory abilities. Autologous and allogeneic ex-vivo expanded human MSC have been utilized to treat aGVHD with promising results, but the mechanisms of therapeutic action remain unclear. Here a robust humanized mouse model of aGVHD based on delivery of human peripheral blood mononuclear cells (PBMC) to non-obese diabetic (NOD)-severe combined immunodeficient (SCID) interleukin (IL)-2rγ(null) (NSG) mice was developed that allowed the exploration of the role of MSC in cell therapy. MSC therapy resulted in the reduction of liver and gut pathology and significantly increased survival. Protection was dependent upon the timing of MSC therapy, with conventional MSC proving effective only after delayed administration. In contrast, interferon (IFN)-γ-stimulated MSC were effective when delivered with PBMC. The beneficial effect of MSC therapy in this model was not due to the inhibition of donor PBMC chimerism, as CD45(+) and T cells engrafted successfully in this model. MSC therapy did not induce donor T cell anergy, FoxP3(+) T regulatory cells or cause PBMC apoptosis in this model; however, it was associated with the direct inhibition of donor CD4(+) T cell proliferation and reduction of human tumour necrosis factor-α in serum.

Fabrication of CaO-NaO-SiO(2)/TiO (2) scaffolds for surgical applications

A series of titanium (Ti) based glasses were formulated (0.62 SiO(2)-0.14 Na(2)O-0.24 CaO, with 0.05 mol% TiO(2) substitutions for SiO(2)) to develop glass/ceramic scaffolds for bone augmentation. Glasses were initially characterised using X-ray diffraction (XRD) and particle size analysis, where the starting materials were amorphous with 4.5 μm particles. Hot stage microscopy and high temperature XRD were used to determine the sintering temperature (~700 °C) and any crystalline phases present in this region (Na(2)Ca(3)Si(6)O(16), combeite and quartz). Hardness testing revealed that the Ti-free control (ScC-2.4 GPa) had a significantly lower hardness than the Ti-containing materials (Sc1 and Sc2 ~6.6 GPa). Optical microscopy determined pore sizes ranging from 544 to 955 μm. X-ray microtomography calculated porosity from 87 to 93 % and surface area measurements ranging from 2.5 to 3.3 SA/mm(3). Cytotoxicity testing (using mesenchymal stem cells) revealed that all materials encouraged cell proliferation, particularly the higher Ti-containing scaffolds over 24-72 h.

Understanding Solvent Effects in the Solvolyses of 4-Fluorophenyl Chlorothionoformate

The solvolyses of 4-fluorophenyl chlorothionoformate (1) are studied in fifteen binary aqueous organic mixtures of widely varying nucleophilicity and ionizing power values. The specific rates of solvolyses of 1 are plotted against the specific rates of solvolysis observed for phenyl chloroformate (2) and deviations from the line-of-best-fit are observed in some of the highly ionizing aqueous fluoroalcohol mixtures. An analysis of the solvolytic data accumulated using the extended (two-term) Grunwald-Winstein equation confirms this deviant behavior and shows that dual bimolecular addition-elimination and unimolecular ionization channels occur in the solvolyses of 1.

Allogeneic mesenchymal stem cells prevent allergic airway inflammation by inducing murine regulatory T cells

BACKGROUND

Adult bone marrow-derived mesenchymal stem cells (MSC) possess potent immune modulatory effects which support their possible use as a therapy for immune-mediated disease. MSC induce regulatory T cells (T(reg)) in vitro although the in vivo relevance of this is not clear.

OBJECTIVE

This study addressed the hypothesis that adult bone marrow derived-MSC would prevent the pathology associated with allergen-driven airway inflammation, and sought to define the effector mechanism.

METHODS

The influence of allogeneic MSC was examined in a model system where T(reg) induction is essential to prevent pathology. This was tested using a combination of a model of ovalbumin-driven inflammation with allogeneic MSC cell therapy.

RESULTS

Systemic administration of allogeneic MSC protected the airways from allergen-induced pathology, reducing airway inflammation and allergen-specific IgE. MSC were not globally suppressive but induced CD4(+) FoxP3(+) T cells and modulated cell-mediated responses at a local and systemic level, decreasing IL-4 but increasing IL-10 in bronchial fluid and from allergen re-stimulated splenocytes. Moderate dose cyclophosphamide protocols were used to differentially ablate T(reg) responses; under these conditions the major beneficial effect of MSC therapy was lost, suggesting induction of T(reg) as the key mechanism of action by MSC in this model. In spite of the elimination of T(reg) , a significant reduction in airway eosinophilia persisted in those treated with MSC.

CONCLUSION

These data demonstrate that MSC induce T(reg) in vivo and reduce allergen-driven pathology. Multiple T(reg) dependent and independent mechanisms of therapeutic action are employed by MSC.

Zinc and silver glass polyalkenoate cements: an evaluation of their antibacterial nature

A biofilm is an accumulation of micro-organisms and their extracellular products forming a structured community on a surface. Biofilm formation on medical devices has severe health consequences as bacteria growing in this lifestyle are tolerant to both host defence mechanisms and antibiotic therapies. However, silver and zinc ions inhibit the attachment and proliferation of immature biofilms. The objective of this study is to evaluate whether silver and zinc ions eluted from novel glass polyalkenoate cement (GPC) coatings have the ability to inhibit Methicillin-resistant Staphylococcus aureus (MRSA) in vivo. A silver and zinc-containing GPC coating was synthesised, deposited onto Ti6Al4V discs and placed in a specified amount of analytical water for 1, 7 and 30 days. The resulting elutes were collected and Atomic absorption spectroscopy was used to measure ion release. The elutes were injected into Galleria mellonella larvae infected with MRSA and the antibacterial properties of these elutes were evaluated in vivo. The majority of the zinc and silver ions were released within the first 24 h; this corresponded with the greatest degree of protection observed in infected larvae. Results were compared to a conventional in vitro model where identical elutes were incubated with MRSA on nutrient agar. These results were consistent with those observed in the larval model, demonstrating a reduction in bacterial viability when co-cultured with elutes for 2 h. This work confirms the promise of the Galleria mellonella as a model for the assessment of antimicrobial agents and demonstrates the capacity of novel silver and zinc-containing GPCs to retard the colonisation of MRSA.

Analysis of the nucleophilic solvation effects in isopropyl chlorothioformate solvolysis

Correlation of the solvent effects through application of the extended Grunwald-Winstein equation to the solvolysis of isopropyl chlorothioformate results in a sensitivity value of 0.38 towards changes in solvent nucleophilicity (l) and a sensitivity value of 0.72 towards changes in solvent ionizing power (m). This tangible l value coupled with the negative entropies of activation observed indicates a favorable predisposition towards a modest rear-side nucleophilic solvation of a developing carbocation. Only in 100% ethanol was the bimolecular pathway dominant. These observations are very different from those obtained for the solvolysis of isopropyl chloroformate, where dual reaction channels were proposed, with the addition-elimination reaction favored in the more nucleophilic solvents and a unimolecular fragmentation-ionization mechanism favored in the highly ionizing solvents.

Attenuated Bordetella pertussis vaccine strain BPZE1 modulates allergen-induced immunity and prevents allergic pulmonary pathology in a murine model

BACKGROUND

Virulent Bordetella pertussis, the causative agent of whooping cough, exacerbates allergic airway inflammation in a murine model of ovalbumin (OVA) sensitization. A live genetically attenuated B. pertussis mucosal vaccine, BPZE1, has been developed that evokes full protection against virulent challenge in mice but the effect of this attenuated strain on the development of allergic responses is unknown.

OBJECTIVE

To assess the influence of attenuated B. pertussis BPZE1 on OVA priming in a murine model of allergic airway inflammation.

METHODS

Mice were challenged with virulent or attenuated strains of B. pertussis, and sensitized to allergen (OVA) at the peak of bacterial carriage. Subsequently, airway pathology, local inflammation and OVA-specific immunity were examined.

RESULTS

In contrast to virulent B. pertussis, live BPZE1 did not exacerbate but reduced the airway pathology associated with allergen sensitization. BPZE1 immunization before allergen sensitization did not have an adjuvant effect on allergen specific IgE but resulted in a statistically significant decrease in airway inflammation in tissue and bronchoalveolar lavage fluid. BPZE1 significantly reduced the levels of OVA-driven IL-4, IL-5 and IL-13 but induced a significant increase in IFN-gamma in response to OVA re-stimulation.

CONCLUSIONS

These data demonstrate that, unlike virulent strains, the candidate attenuated B. pertussis vaccine BPZE1 does not exacerbate allergen-driven airway pathology. BPZE1 may represent an attractive T-helper type 1 promoting vaccine candidate for eradication of whooping cough that is unlikely to promote atopic disease.

Cell contact, prostaglandin E(2) and transforming growth factor beta 1 play non-redundant roles in human mesenchymal stem cell induction of CD4+CD25(High) forkhead box P3+ regulatory T cells

Adult human mesenchymal stromal or stem cells (MSC) can differentiate into a variety of cell types and are candidate cellular therapeutics in regenerative medicine. Surprisingly, these cells also display multiple potent immunomodulatory capabilities, including allosuppression, making allogeneic cell therapy a possibility. The exact mechanisms involved in regulatory T cell induction by allogeneic human MSC was examined, using purified CD4+ populations and well-characterized bone marrow-derived adult human MSC. Allogeneic MSC were shown to induce forkhead box P3 (FoxP3)+ and CD25+ mRNA and protein expression in CD4+ T cells. This phenomenon required direct contact between MSC and purified T cells, although cell contact was not required for MSC induction of FoxP3 expression in an unseparated mononuclear cell population. In addition, through use of antagonists and neutralizing antibodies, MSC-derived prostaglandins and transforming growth factor (TGF)-beta1 were shown to have a non-redundant role in the induction of CD4+CD25+FoxP3+ T cells. Purified CD4+CD25+ T cells induced by MSC co-culture expressed TGF-beta1 and were able to suppress alloantigen-driven proliferative responses in mixed lymphocyte reaction. These data clarify the mechanisms of human MSC-mediated allosuppression, supporting a sequential process of regulatory T cell induction involving direct MSC contact with CD4+ cells followed by both prostaglandin E(2) and TGF-beta1 expression. Overall, this study provides a rational basis for ongoing clinical studies involving allogeneic MSC.

Interferon-gamma does not break, but promotes the immunosuppressive capacity of adult human mesenchymal stem cells

The ability of mesenchymal stem cells (MSC) to suppress alloresponsiveness is poorly understood. Herein, an allogeneic mixed lymphocyte response was used as a model to investigate the mechanisms of MSC-mediated immunomodulation. Human MSC are demonstrated to express the immunosuppressive cytokines hepatocyte growth factor (HGF), interleukin (IL)-10 and transforming growth factor (TGF)-beta1 at concentrations that suppress alloresponses in vitro. MSC also express cyclooxygenase 1 and 2 and produce prostaglandin E2 constitutively. Blocking studies with indomethacin confirmed that prostaglandins contribute to MSC-mediated allosuppression. The proinflammatory cytokine interferon (IFN)-gamma did not ablate MSC inhibition of alloantigen-driven proliferation but up-regulated HGF and TGF-beta1. IFN-gamma also induced expression of indoleamine 2,3, dioxygenase (IDO), involved in tryptophan catabolism. Use of an antagonist, 1-methyl-L-tryptophan, restored alloresponsiveness and confirmed an IDO contribution to IFN-gamma-induced immunomodulation by MSC. Addition of the tryptophan catabolite kynurenine to mixed lymphocyte reactions (MLR), blocked alloproliferation. These findings support a model where IDO exerts its effect through the local accumulation of tryptophan metabolites rather than through tryptophan depletion. Taken together, these data demonstrate that soluble factors, or products derived from MSC, modulate immune responses and suggest that MSC create an immunosuppressive microenvironment capable of modulating alloresponsiveness even in the presence of IFN-gamma.

gammadelta T cells regulate the early inflammatory response to bordetella pertussis infection in the murine respiratory tract

The role of gammadelta T cells in the regulation of pulmonary inflammation following Bordetella pertussis infection was investigated. Using a well-characterized murine aerosol challenge model, inflammatory events in mice with targeted disruption of the T-cell receptor delta-chain gene (gammadelta TCR-/- mice) were compared with those in wild-type animals. Early following challenge with B. pertussis, gammadelta TCR-/- mice exhibited greater pulmonary inflammation, as measured by intra-alveolar albumin leakage and lesion histomorphometry, yet had lower contemporaneous bacterial lung loads. The larger numbers of neutrophils and macrophages and the greater concentration of the neutrophil marker myeloperoxidase in bronchoalveolar lavage fluid from gammadelta TCR-/- mice at this time suggested that differences in lung injury were mediated through increased leukocyte trafficking into infected alveoli. Furthermore, flow cytometric analysis found the pattern of recruitment of natural killer (NK) and NK receptor+ T cells into airspaces differed between the two mouse types over the same time period. Taken together, these findings suggest a regulatory influence for gammadelta T cells over the early pulmonary inflammatory response to bacterial infection. The absence of gammadelta T cells also influenced the subsequent adaptive immune response to specific bacterial components, as evidenced by a shift from a Th1 to a Th2 type response against the B. pertussis virulence factor filamentous hemagglutinin in gammadelta TCR-/- mice. The findings are relevant to the study of conditions such as neonatal B. pertussis infection and acute respiratory distress syndrome where gammadelta T cell dysfunction has been implicated in the inflammatory process.

Prior Bordetella pertussis infection modulates allergen priming and the severity of airway pathology in a murine model of allergic asthma

BACKGROUND

It has been proposed that T helper (Th)2-driven immune deviation in early life can be countered by Th1 inducing childhood infections and that such counter-regulation can protect against allergic asthma.

OBJECTIVE

To test whether Th1-inducing infection with Bordetella pertussis protects against allergic asthma using well-characterized murine models.

METHODS

Groups of mice were sensitized to ovalbumin (OVA) in the presence or absence of B. pertussis, a well-characterized Th1 inducing respiratory infection. Immunological, pathological and physiological parameters were measured to assess the impact of infection on immune deviation and airway function.

RESULTS

We demonstrate that OVA sensitization does not affect the development of B. pertussis-specific immune responses dominated by IgG2a and IFN-gamma and does not impair Th1-mediated clearance of airway infection. In contrast, B. pertussis infection at the time of sensitization modulated the response to OVA and significantly reduced total serum and OVA-specific IgE. The pattern of cytokine responses, in particular OVA-specific IL-5 responses in the spleen was also modulated. However, B. pertussis did not cause global suppression as IL-10 and IL-13 levels were enhanced in OVA-stimulated spleen cell cultures and in lavage fluid from infected co-sensitized mice. Histopathological examination revealed that B. pertussis infection prior to OVA sensitization resulted in increased inflammation of bronchiolar walls with accompanying hyperplasia and mucous metaplasia of lining epithelia. These pathological changes were accompanied by increased bronchial hyper-reactivity to methacholine exposure.

CONCLUSION

Contrary to the above premise, a Th1 response induced by a common childhood infection does not protect against bronchial hyper-reactivity, but rather exacerbates the allergic asthmatic response, despite modulation of immune mediators.

High-sensitivity PCR detection of parvovirus B19 in plasma

Parvovirus B19 (B19) is a human pathogen transmitted to susceptible individuals via respiratory secretions and contaminated blood or blood products. B19 levels in pooled plasma of less than 10(4) genome equivalents/ml may not be infectious, while those greater than 10(7)/ml are capable of transmitting infection. A World Health Organization (WHO) B19 DNA international standard has been recently introduced. The purpose of the present work was to develop a PCR-enzyme-linked immunosorbent assay (PCR-ELISA) calibrated against the WHO B19 DNA international standard which could easily and reliably detect B19 DNA levels in plasma above 10(4) IU/ml (6.5 x 10(3) genome equivalents/ml). A B19 PCR-ELISA system was developed which uses a dinitrophenylated oligonucleotide probe to detect immobilized biotinylated amplicons following single-round PCR amplification. The level of B19 DNA (in international units per milliliter) in individual and pooled plasma specimens was evaluated. Proteinase K treatment of plasma was found to be sufficient to quantitatively release B19 DNA. The B19 PCR-ELISA had a sensitivity of detection of 1.6 x 10(3) IU/ml B19 DNA and a dynamic range extending from 8 to 1,000 IU of B19 DNA (equivalent to 1.6 x 10(3) to 2 x 10(5) IU of B19 DNA/ml). Furthermore, the antibody profile of pooled plasma products was determined in terms of B19 immunoglobulin G (IgG) (in international units per milliliter). The B19 IgG level was found to be 64.7 +/- 17.5 IU/ml (mean +/- standard deviation). The B19 PCR-ELISA, which is calibrated against the B19 DNA international standard, may have an application for the rapid screening of plasma minipools for B19 DNA, thereby leading to an improvement in blood product safety.

Baculovirus expression of parvovirus B19 (B19V) NS1: utility in confirming recent infection

BACKGROUND

The presence of anti-parvovirus B19 (B19V) IgM against viral capsid proteins (VP1 and VP2) has long been used to detect recent infection. The utility of antibodies directed against B19V NS1 protein has received less attention as a serological indicator of recent infection, although anti-B19V NS1 IgG has been associated with persistent infection.

OBJECTIVES

To elucidate the role of anti-B19V NS1 antibody detection in recent infection, full-length B19V NS1 was expressed and purified. The resultant antigen was used to develop both Western blot assays and microplate ELISA for the detection of NS1 antibodies.

STUDY DESIGN

Serum specimens were obtained from individuals recently infected with B19V (children (n=16), adults (n=40)) and from 17 individuals with no evidence of recent B19V infection. All specimens were screened for anti-B19V NS1 IgG and IgM.

RESULTS

It was observed that 68.8% (11/16) of children recently infected with B19V were anti-B19V NS1 IgG seropositive. Furthermore, 27.5% (11/40) anti-B19V VP2 IgM positive specimens also contained anti-B19V NS1 IgM when tested by ELISA, while no reactivity was observed following Western blot analysis, possibly due to the absence of conformational epitopes.

CONCLUSIONS

Anti-B19V NS1 IgM detection may have utility in the confirmation of recent infection with B19V.

The rational design of vaccine adjuvants for mucosal and neonatal immunization

There is an urgent requirement for neonatal vaccines that induce effective and long-lasting immune responses at the mucosal surfaces of the gut and respiratory tract. The delay in their development has been due in part to a lack of understanding of the mucosal and neonatal immune systems. This work reviews recent advances in the understanding of the cells and molecules that mediate immunity, describing the importance of different T helper populations in determining the success of vaccination strategies. These advances have allowed the rational design of novel vaccine adjuvants and delivery systems that can selectively induce immunity at different anatomical sites mediated by distinct T cell populations. Five functional classes of adjuvant are described. These exploit mechanisms which a) create an antigen depot, b) preserve antigen conformation, c) direct antigen to specific immune cells, d) induce mucosal responses and e) induce cytotoxic T cell responses. Comparisons are made between the chemical structures of bacterial toxins and non-toxic derivatives that retain adjuvanticity. The concept of DNA immunization is introduced and the advantages and disadvantages of this novel approach are discussed. The specific problems relating to neonatal immunization are explored with particular reference to the functional immaturity of the neonatal immune system and interference by maternal antibody. Finally, recent work suggesting that there is no intrinsic barrier to designing effective neonatal vaccines deliverable by the mucosal route is discussed.

Impaired gamma interferon responses against parvovirus B19 by recently infected children

Parvovirus B19 is the causative agent of "fifth disease" of childhood. It has been implicated in a variety of conditions, including unsuccessful pregnancy and rheumatoid arthritis, and is a potential contaminant of blood products. There has been little study of immunity to parvovirus B19, and the exact nature of the protective humoral and cell-mediated immune response is unclear. Immune responses to purified virus capsid proteins, VP1 and VP2, were examined from a cohort of recently infected children and compared with responses from long-term convalescent volunteers. The results demonstrate that antibody reactivity is primarily maintained against conformational epitopes in VP1 and VP2. The unique region of VP1 appears to be a major target for cell-mediated immune responses, particularly in recently infected individuals. We confirm that antibody reactivity against linear epitopes of VP2 is lost shortly after infection but find no evidence of the proposed phenotypic switch in either the subclass of parvovirus B19-specific antibody or the pattern of cytokine production by antigen-specific T cells. The dominant subclass of specific antibody detected from both children and adults was immunoglobulin G1. No evidence was found for interleukin 4 (IL-4) or IL-5 production by isolated lymphocytes from children or adults. In contrast, lymphocytes from convalescent adults produced a typical type 1 response associated with high levels of IL-2 and gamma interferon (IFN-gamma). However, we observed a significant (P<0.001) deficit in the production of IFN-gamma in response to VP1 or VP2 from lymphocytes isolated from children. Taken together, these results imply that future parvovirus B19 vaccines designed for children will require the use of conformationally preserved capsid proteins incorporating Th1 driving adjuvants. Furthermore, these data suggest novel mechanisms whereby parvovirus B19 infection may contribute to rheumatoid arthritis and unsuccessful pregnancy.