Glutathione S-transferases. The first enzymatic step in mercapturic acid formation.

Evolution by gene duplication

Signal transduction is initiated by complex protein-protein interactions between ligands, receptors and kinases, to name only a few. It is now becoming clear that lipid micro-environments on the cell surface -- known as lipid rafts -- also take part in this process. Lipid rafts containing a given set of proteins can change their size and composition in response to intra- or extracellular stimuli. This favours specific protein-protein interactions, resulting in the activation of signalling cascades.

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Lipid rafts and signal transduction

Authors Jan L. Brozek, MD, PhD – Department of Clinical Epidemiology & Biostatistics and Medicine, McMaster University, Hamilton, Canada Jean Bousquet, MD, PhD – Service des Maladies Respiratoires, Hopital Arnaud de Villeneuve, Montpellier, France, INSERM, CESP U1018, Respiratory and Environmental Epidemiology Team, France, and WHO Collaborating Center for Rhinitis and Asthma Carlos E. Baena-Cagnani, MD – Faculty of Medicine, Catholic University of Cordoba, Cordoba, Argentina Sergio Bonini, MD – Institute of Neurobiology and Molecular Medicine – CNR, Rome, Italy and Department of Medicine, Second University of Naples, Naples, Italy G. Walter Canonica, MD – Allergy & Respiratory Diseases, DIMI, Department of Internal Medicine, University of Genoa, Genoa, Italy Thomas B. Casale, MD – Division of Allergy and Immunology, Department of Medicine, Creighton University, Omaha, Nebraska, USA Roy Gerth van Wijk, MD, PhD – Section of Allergology, Department of Internal Medicine, Erasmus Medical Centre, Rotterdam, the Netherlands Ken Ohta, MD, PhD – Division of Respiratory Medicine and Allergology, Department of Medicine, Teikyo University School of Medicine, Tokyo, Japan Torsten Zuberbier, MD – Department of Dermatology and Allergy, Charite Universitatsmedizin Berlin, Berlin, Germany Holger J. Schunemann, MD, PhD, MSc – Department of Clinical Epidemiology & Biostatistics and Medicine, McMaster University, Hamilton, Canada

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Allergic Rhinitis and Its Impact on Asthma

S107, a phosphocholine-binding myeloma protein, has been cloned in soft agar, and an antigen-binding variant has been isolated and characterized. The variant does not bind phosphocholine attached to carrier or as free hapten in solution but does retain antigenic determinants (idiotypes) of the parent. Chain recombination experiments suggest that the defect in binding is entirely in the heavy chain. Amino acid sequence analysis showed a single substitution--glutamic acid to alanine at position 35--in the first hypervariable or complementarity-determining region. In terms of the three-dimensional model of the phosphocholine-binding site, glutamic acid-35 provides a hydrogen bond to tyrosine-94 of the light chain that appears to be critical for stability of this portion of the binding site. The removal of this bond and the presence of the smaller alanine side chain is thus consistent with the loss in binding activity. These results suggest that small numbers of substitutions in antibodies, such as those presumably introduced by somatic mutation, may in some situations be effective in altering antigen-binding specificity.

https://www.pnas.org/content/pnas/79/6/1979.full.pdf

Single amino acid substitution altering antigen-binding specificity

This review is about one of the physiologically important macromolecules that interact with the Fc domains of immunoglobulins. Such substances (complement, "immunoglobulin binding factors," Fc receptors) can convert the simp le binding of antigen to antibody into a biologically meaningful event. The protein we review he re-the Fc receptor with high affinity for monomeric immunoglobulin E (IgE}-is only one of several proteins that interact with IgE (1-5). In addition to high affinity, its special characteristic is its distribution on the plasma membrane of mast cells and basophils exclusively. Activation of this receptor initiates release of preformed mediators contained in int racellular granules and the biosynthesis of a variety of biologically active lipids such as the leukotrienes. Here we review what is known about the structure of this receptor and the early biochemical events that it initiates. We do not consider the conse quences of

The Receptor with High Affinity for Immunoglobulin E

The high-affinity receptor for immunoglobulin E, Fcɛ RI, is found exclusively on mast cells and basophils. When multivalent aller-gens bind to the receptor-bound IgE, the consequent aggregation of the receptors leads to the release of mediators responsible for allergic symptoms. In rodents Fcɛ RI is a tetrameric complex of non-covalently attached subunits: one IgE-binding α subunit, one β subunit and a dimer of disulphide-linked γ subunits1. Com-plementary DNA encoding the α and the β subunits has recently been isolated2–5, but expression of IgE-binding by transfected cells has not yet been achieved2–5. Here we report the cloning of cDNA for the γ subunit, and propose a model for the αβγ2 tetramer which accounts for many of the structural features of the receptor. The rodent receptor on the surface of COS 7 cells was expressed only when the cDNAs for all three subunits were cotransfected. Successful expression of human IgE receptors should now be possible, eventually to permit the detailed analysis of the human IgE-receptor interaction and assist the search for therapeutically effective inhibitors.

Complete structure and expression in transfected cells of high affinity IgE receptor

Rat immunoglobulin E (IgE) was treated with a crosslinking reagent, dimethyl suberimidate, and fractionated by gel filtration into monomers, dimers, trimers, and higher polymers The fractions retained substantial ability to bind specifically to mast cells About one-third of the cell-bound dimers appeared to bind bivalently The fractions were assayed in vivo by passive cutaneous anaphylaxis in rats, and for histamine or serotonin release in vitro using normal or tumor mouse mast cells The monomers showed no activity, while the dimers and higher polymers gave excellent and approximately equivalent responses We conclude that IgE that has been crosslinked to form dimers prior to the addition to mast cells can serve as a unit signal for triggering IgE-mediated exocytosis

https://www.pnas.org/content/pnas/74/7/2993.full.pdf

Dimeric immunoglobulin E serves as a unit signal for mast cell degranulation.

Affinity labeling of a phosphorylcholine binding mouse myeloma protein.

Previous studies indicated that cultured rat basophilic leukemia cells have surface receptors which bind IgE with high specificity. In this paper we describe some quantitative aspects of the phenomenon. The reaction mechanism appears to consist of a simple reversible binding reaction with k1 = 9.6 x 104 M–1 sec–1 and k–1 ⩽ 1.6 x 10–5 sec–1 at 37°C. The calculated KA is therefore ⩾ 6 x 109 M–1. The activation energy of binding was found to be 7.8 kcal/mol. The number of binding sites/cell varied between 3 x 105 to over 1 x 106. The binding was insensitive to pH's between 6–8 but at pH 3.0 complete dissociation of bound IgE occurred in ∼ 1 min at 0°C leaving the receptors for IgE intact. Ca++ plus EDTA and Mg++ plus EDTA produce a fairly marked reduction in binding capacity though these reagents alone produce much smaller effects.

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Henry Metzger

Papers

The Receptor with High Affinity for Immunoglobulin E

Complete structure and expression in transfected cells of high affinity IgE receptor

Dimeric immunoglobulin E serves as a unit signal for mast cell degranulation.

Affinity labeling of a phosphorylcholine binding mouse myeloma protein.

THE INTERACTION OF IgE WITH RAT BASOPHILIC LEUKEMIA CELLS : II. Quantitative Aspects of the Binding Reaction