Biochemical characterization of human eosinophil Charcot-Leyden crystal protein (lysophospholipase)

The Pathology of Asthma: What Is Obstructing Our View?

Despite the advent of sophisticated and efficient new biologics to treat inflammation in asthma, the disease persists. Even following treatment, many patients still experience the well-known symptoms of wheezing, shortness of breath, and coughing. What are we missing? Here we examine the evidence that mucus plugs contribute to a substantial portion of disease, not only by physically obstructing the airways but also by perpetuating inflammation. In this way, mucus plugs may act as an immunogenic stimulus even in the absence of allergen or with the use of current therapeutics. The alterations of several parameters of mucus biology, driven by type 2 inflammation, result in sticky and tenacious sputum, which represents a potent threat, first due to the difficulties in expectoration and second by acting as a platform for viral, bacterial, or fungal colonization that allows exacerbations. Therefore, in this way, mucus plugs are an overlooked but critical feature of asthmatic airway disease.

Can (We Make) Bacillus thuringiensis Crystallize More Than Its Toxins?

The development of finely tuned and reliable crystallization processes to obtain crystalline formulations of proteins has received growing interest from different scientific fields, including toxinology and structural biology, as well as from industry, notably for biotechnological and medical applications. As a natural crystal-making bacterium, Bacillus thuringiensis (Bt) has evolved through millions of years to produce hundreds of highly structurally diverse pesticidal proteins as micrometer-sized crystals. The long-term stability of Bt protein crystals in aqueous environments and their specific and controlled dissolution are characteristics that are particularly sought after. In this article, we explore whether the crystallization machinery of Bt can be hijacked as a means to produce (micro)crystalline formulations of proteins for three different applications: (i) to develop new bioinsecticidal formulations based on rationally improved crystalline toxins, (ii) to functionalize crystals with specific characteristics for biotechnological and medical applications, and (iii) to produce microcrystals of custom proteins for structural biology. By developing the needs of these different fields to figure out if and how Bt could meet each specific requirement, we discuss the already published and/or patented attempts and provide guidelines for future investigations in some underexplored yet promising domains.

Charcot-Leyden crystals and other protein crystals driving type 2 immunity and allergy

Protein crystals derived from innate immune cells have been synonymous with a Type-2 immune response in both mouse and man for over 150 years. Eosinophilic Galectin-10 (Charcot-Leyden) crystals in humans, and Ym1/Ym2 crystals in mice are frequently found in the context of parasitic infections, but also in diseases such as asthma and chronic rhinosinusitis. Despite their notable presence, these crystals are often overlooked as trivial markers of Type-2 inflammation. Here, we discuss the source, context, and role of protein crystallization. We focus on similarities observed between Galectin-10 and Ym1/2 crystals in driving immune responses; the subsequent benefit to the host during worm infection, and conversely the detrimental exacerbation of inflammation and mucus production during asthma.

The Charcot-Leyden crystal protein revisited-A lysopalmitoylphospholipase and more

The Charcot-Leyden crystal protein (CLC-P), a constituent of human and not mouse eosinophils, is one of the most abundant proteins within human eosinophils. It has a propensity to form crystalline structures, Charcot-Leyden crystals, which are hallmarks in their distinctive extracellular crystalline forms as markers of eosinophilic inflammation. The functions of CLC-P within eosinophils have been uncertain. Although the action of CLC-P as a lysophospholipase has been questioned, assays of chromatographically purified CLC-P and crystal-derived CLC-P as well as studies of transfected recombinant CLC-P have consistently documented that CLC-P endogenously expresses lysophospholipase activity, releasing free palmitate from substrate lysopalmitoylphosphatidylcholine. Rather than acting solely as a hydrolytic enzyme to release palmitate from a lysolipid substrate, some other lysophospholipases function more dominantly as acyl-protein thioesterases (APTs), enzymes that catalyze the removal of thioester-linked, long chain fatty acids, such as palmitate, from cysteine residues of proteins. As such APTs participate in palmitoylation, a post-translational modification that can affect membrane localization, vesicular transport, and secretion. CLC-P has attributes of an APT. Thus, whereas CLC-P expresses inherent lysophospholipase activity, like some other lysophospholipase enzymes, it likely also functions in regulating the dynamic palmitoylation cycle, including, given its dominant subplasmalemmal location, at the human eosinophil's plasma membrane.

Charcot-Leyden crystal protein/galectin-10 interacts with cationic ribonucleases and is required for eosinophil granulogenesis

BACKGROUND

The human eosinophil Charcot-Leyden crystal (CLC) protein is a member of the Galectin superfamily and is also known as galectin-10 (Gal-10). CLC/Gal-10 forms the distinctive hexagonal bipyramidal crystals that are considered hallmarks of eosinophil participation in allergic responses and related inflammatory reactions; however, the glycan-containing ligands of CLC/Gal-10, its cellular function(s), and its role(s) in allergic diseases are unknown.

OBJECTIVE

We sought to determine the binding partners of CLC/Gal-10 and elucidate its role in eosinophil biology.

METHODS

Intracellular binding partners were determined by ligand blotting with CLC/Gal-10, followed by coimmunoprecipitation and coaffinity purifications. The role of CLC/Gal-10 in eosinophil function was determined by using enzyme activity assays, confocal microscopy, and short hairpin RNA knockout of CLC/Gal-10 expression in human CD34⁺ cord blood hematopoietic progenitors differentiated to eosinophils.

RESULTS

CLC/Gal-10 interacts with both human eosinophil granule cationic ribonucleases (RNases), namely, eosinophil-derived neurotoxin (RNS2) and eosinophil cationic protein (RNS3), and with murine eosinophil-associated RNases. The interaction is independent of glycosylation and is not inhibitory toward endoRNase activity. Activation of eosinophils with INF-γ induces the rapid colocalization of CLC/Gal-10 with eosinophil-derived neurotoxin/RNS2 and CD63. Short hairpin RNA knockdown of CLC/Gal-10 in human cord blood-derived CD34⁺ progenitor cells impairs eosinophil granulogenesis.

CONCLUSIONS

CLC/Gal-10 functions as a carrier for the sequestration and vesicular transport of the potent eosinophil granule cationic RNases during both differentiation and degranulation, enabling their intracellular packaging and extracellular functions in allergic inflammation.

Protein crystallization promotes type 2 immunity and is reversible by antibody treatment

Although spontaneous protein crystallization is a rare event in vivo, Charcot-Leyden crystals (CLCs) consisting of galectin-10 (Gal10) protein are frequently observed in eosinophilic diseases, such as asthma. We found that CLCs derived from patients showed crystal packing and Gal10 structure identical to those of Gal10 crystals grown in vitro. When administered to the airways, crystalline Gal10 stimulated innate and adaptive immunity and acted as a type 2 adjuvant. By contrast, a soluble Gal10 mutein was inert. Antibodies directed against key epitopes of the CLC crystallization interface dissolved preexisting CLCs in patient-derived mucus within hours and reversed crystal-driven inflammation, goblet-cell metaplasia, immunoglobulin E (IgE) synthesis, and bronchial hyperreactivity (BHR) in a humanized mouse model of asthma. Thus, protein crystals may promote hallmark features of asthma and are targetable by crystal-dissolving antibodies.

Charcot-Leyden Crystals in Eosinophilic Inflammation: Active Cytolysis Leads to Crystal Formation

PURPOSE OF REVIEW

Charcot-Leyden crystals (CLCs), slender bipyramidal hexagonal crystals, were first described by Jean-Martin Charcot in 1853, predating Paul Ehrlich's "discovery" of eosinophils by 26 years. To date, CLCs are known as a classical hallmark of eosinophilic inflammation. CLC protein expresses palmitate cleaving lysophospholipase activity and is a member of the family of S-type lectins, galectin-10. We summarize current knowledge regarding the pathological observations of CLCs and their mechanism of generation focusing on eosinophil cell death.

RECENT FINDINGS

The presence of CLCs in vivo has been consistently associated with lytic eosinophils. Recent evidence revealed that cytolysis represents the occurrence of extracellular trap cell death (ETosis), an active non-apoptotic cell death process releasing filamentous chromatin structure. Galectin-10 is a predominant protein present within the cytoplasm of eosinophils but not stored in secretory granules. Activated eosinophils undergo ETosis and loss of galectin-10 cytoplasmic localization results in intracellular CLC formation. Free galectin-10 released following plasma membrane disintegration forms extracellular CLCs. Of interest, galectin-10-containing extracellular vesicles are also released during ETosis. Mice models indicated that CLCs could be a novel therapeutic target for Th2-type airway inflammation. The concept of ETosis, which represents a major fate of activated eosinophils, expands our current understanding by which cytoplasmic galectin-10 is crystalized/externalized. Besides CLCs and free galectin-10, cell-free granules, extracellular chromatin traps, extracellular vesicles, and other alarmins, all released through the process of ETosis, have novel implications in various eosinophilic disorders.

Protein crystallization in living cells

Protein crystallization in living cells has been observed surprisingly often as a native assembly process during the past decades, and emerging evidence indicates that this phenomenon is also accessible for recombinant proteins. But only recently the advent of high-brilliance synchrotron sources, X-ray free-electron lasers, and improved serial data collection strategies has allowed the use of these micrometer-sized crystals for structural biology. Thus, in cellulo crystallization could offer exciting new possibilities for proteins that do not crystallize applying conventional approaches. In this review, we comprehensively summarize the current knowledge of intracellular protein crystallization. This includes an overview of the cellular functions, the physical properties, and, if known, the mode of regulation of native in cellulo crystal formation, complemented with a discussion of the reported crystallization events of recombinant proteins and the current method developments to successfully collect X-ray diffraction data from in cellulo crystals. Although the intracellular protein self-assembly mechanisms are still poorly understood, regulatory differences between native in cellulo crystallization linked to a specific function and accidently crystallizing proteins, either disease associated or recombinantly introduced, become evident. These insights are important to systematically exploit living cells as protein crystallization chambers in the future.

A Brief History of Charcot-Leyden Crystal Protein/Galectin-10 Research

Eosinophils are present in tissues, such as the respiratory tract, spleen, lymph nodes and blood vessels. The significant presence of eosinophils in these tissues are associated with various diseases, including asthma, allergies, acute myeloid leukemia, etc. Charcot-Leyden crystal protein/galectin-10 is overexpressed in eosinophils and has also been identified in basophils and macrophages. In human body, this protein could spontaneously form Charcot-Leyden crystal in lymphocytes or in the lysates of lymphocytes. At present, the role of Charcot-Leyden crystal protein/galectin-10 in lymphocytes is not fully understood. This review summarizes research progress on Charcot-Leyden crystal protein/galectin-10, with emphasis on its history, cellular distributions, relations to diseases, structures and ligand binding specificity.

Charcot-Leyden crystals: do they exist in veterinary species? A case report and literature review

The Charcot-Leyden crystal (CLC) is a major human eosinophil protein that readily crystallizes; these crystals are common in eosinophilic diseases. Although anecdotal existence of these crystals is known in veterinary pathology, definitive reports do not exist, to our knowledge. We identified eosinophilic crystals in a laryngeal myxosarcoma from a 2-y-old, spayed female, Labrador Retriever dog that were tentatively interpreted as CLCs. However, Ziehl-Neelsen acid-fast stain was negative, arguing against CLCs. The crystals stained red with Masson trichrome, precluding collagen. Periodic acid-Schiff and alcian blue were negative. The crystals stained positively with Okajima, and no myoglobin immunoreactivity was detected, supporting their identity as hemoglobin crystals. In the absence of a hematologic abnormality, these crystals were interpreted to be abnormal hemoglobin breakdown products. Protein sequence comparison was pursued to determine whether a protein similar to CLC exists in mammals. Only 3 nonhuman primate species, the Sumatran orangutan ( Pongo abelii), rhesus macaque ( Macaca mulatta), and cynomolgus monkey ( Macaca fascicularis), had a sequence similarity of >80%. Of the crystal-forming residues, 12 of 54 (22%) were different in the Sumatran orangutan and 15 of 54 (28%) were different in the Macaca spp., which may affect the crystallization process. The lack of reports of CLCs in nonhuman species and our results collectively suggest that CLCs are human-specific.

Glycobiology of Eosinophilic Inflammation: Contributions of Siglecs, Glycans, and Other Glycan-Binding Proteins

The historical focus on protein-protein interactions in biological systems, at the expense of attention given to interactions between other classes of molecules, has overlooked important and clinically relevant processes and points of potential clinical intervention. For example, the significance of protein-carbohydrate interactions, especially in the regulation of immune responses, has recently received greater recognition and appreciation. This review discusses several ways by which cell-surface lectin-glycan interactions can modulate eosinophil function, particularly at the levels of eosinophil recruitment and survival, and how such interactions can be exploited therapeutically. A primary focus is on discoveries concerning Siglec-8, a glycan-binding protein selectively expressed on human eosinophils, and its closest functional paralog in the mouse, Siglec-F. Recent advances in the synthesis of polymeric ligands, the identification of physiological ligands for Siglec-8 and Siglec-F in the airway, and the determination of the basis of glycan ligand discrimination of Siglec-8 are discussed. Important similarities and differences between these siglecs are outlined. Eosinophil expression of additional glycan-binding proteins or their glycan ligands, including interactions involving members of the selectin, galectin, and siglec families, is summarized. The roles of these molecules in eosinophil recruitment, survival, and inflammation are described. Finally, the modulation of these interactions and potential therapeutic exploitation of glycan-binding proteins and their ligands to ameliorate eosinophil-associated diseases are considered.

Tissue- and Condition-Specific Isoforms of Mammalian Cytochrome c Oxidase Subunits: From Function to Human Disease

Cytochrome c oxidase (COX) is the terminal enzyme of the electron transport chain and catalyzes the transfer of electrons from cytochrome c to oxygen. COX consists of 14 subunits, three and eleven encoded, respectively, by the mitochondrial and nuclear DNA. Tissue- and condition-specific isoforms have only been reported for COX but not for the other oxidative phosphorylation complexes, suggesting a fundamental requirement to fine-tune and regulate the essentially irreversible reaction catalyzed by COX. This article briefly discusses the assembly of COX in mammals and then reviews the functions of the six nuclear-encoded COX subunits that are expressed as isoforms in specialized tissues including those of the liver, heart and skeletal muscle, lung, and testes: COX IV-1, COX IV-2, NDUFA4, NDUFA4L2, COX VIaL, COX VIaH, COX VIb-1, COX VIb-2, COX VIIaH, COX VIIaL, COX VIIaR, COX VIIIH/L, and COX VIII-3. We propose a model in which the isoforms mediate the interconnected regulation of COX by (1) adjusting basal enzyme activity to mitochondrial capacity of a given tissue; (2) allosteric regulation to adjust energy production to need; (3) altering proton pumping efficiency under certain conditions, contributing to thermogenesis; (4) providing a platform for tissue-specific signaling; (5) stabilizing the COX dimer; and (6) modulating supercomplex formation.

Biomarkers of the involvement of mast cells, basophils and eosinophils in asthma and allergic diseases

Biomarkers of disease activity have come into wide use in the study of mechanisms of human disease and in clinical medicine to both diagnose and predict disease course; as well as to monitor response to therapeutic intervention. Here we review biomarkers of the involvement of mast cells, basophils, and eosinophils in human allergic inflammation. Included are surface markers of cell activation as well as specific products of these inflammatory cells that implicate specific cell types in the inflammatory process and are of possible value in clinical research as well as within decisions made in the practice of allergy-immunology.

Eosinophil granule proteins: form and function

Experimental and clinical data strongly support a role for the eosinophil in the pathogenesis of asthma, allergic and parasitic diseases, and hypereosinophilic syndromes, in addition to more recently identified immunomodulatory roles in shaping innate host defense, adaptive immunity, tissue repair/remodeling, and maintenance of normal tissue homeostasis. A seminal finding was the dependence of allergic airway inflammation on eosinophil-induced recruitment of Th2-polarized effector T-cells to the lung, providing a missing link between these innate immune effectors (eosinophils) and adaptive T-cell responses. Eosinophils come equipped with preformed enzymatic and nonenzymatic cationic proteins, stored in and selectively secreted from their large secondary (specific) granules. These proteins contribute to the functions of the eosinophil in airway inflammation, tissue damage, and remodeling in the asthmatic diathesis. Studies using eosinophil-deficient mouse models, including eosinophil-derived granule protein double knock-out mice (major basic protein-1/eosinophil peroxidase dual gene deletion) show that eosinophils are required for all major hallmarks of asthma pathophysiology: airway epithelial damage and hyperreactivity, and airway remodeling including smooth muscle hyperplasia and subepithelial fibrosis. Here we review key molecular aspects of these eosinophil-derived granule proteins in terms of structure-function relationships to advance understanding of their roles in eosinophil cell biology, molecular biology, and immunobiology in health and disease.

Cytochrome c oxidase subunit 4 isoform 2-knockout mice show reduced enzyme activity, airway hyporeactivity, and lung pathology

Cytochrome c oxidase (COX) is the terminal enzyme of the mitochondrial electron transport chain. The purpose of this study was to analyze the function of lung-specific cytochrome c oxidase subunit 4 isoform 2 (COX4i2) in vitro and in COX4i2-knockout mice in vivo. COX was isolated from cow lung and liver as control and functionally analyzed. COX4i2-knockout mice were generated and the effect of the gene knockout was determined, including COX activity, tissue energy levels, noninvasive and invasive lung function, and lung pathology. These studies were complemented by a comprehensive functional screen performed at the German Mouse Clinic (Neuherberg, Germany). We show that isolated cow lung COX containing COX4i2 is about twice as active (88 and 102% increased activity in the presence of allosteric activator ADP and inhibitor ATP, respectively) as liver COX, which lacks COX4i2. In COX4i2-knockout mice, lung COX activity and cellular ATP levels were significantly reduced (-50 and -29%, respectively). Knockout mice showed decreased airway responsiveness (60% reduced P(enh) and 58% reduced airway resistance upon challenge with 25 and 100 mg methacholine, respectively), and they developed a lung pathology deteriorating with age that included the appearance of Charcot-Leyden crystals. In addition, there was an interesting sex-specific phenotype, in which the knockout females showed reduced lean mass (-12%), reduced total oxygen consumption rate (-8%), improved glucose tolerance, and reduced grip force (-14%) compared to wild-type females. Our data suggest that high activity lung COX is a central determinant of airway function and is required for maximal airway responsiveness and healthy lung function. Since airway constriction requires energy, we propose a model in which reduced tissue ATP levels explain protection from airway hyperresponsiveness, i.e., absence of COX4i2 leads to reduced lung COX activity and ATP levels, which results in impaired airway constriction and thus reduced airway responsiveness; long-term lung pathology develops in the knockout mice due to impairment of energy-costly lung maintenance processes; and therefore, we propose mitochondrial oxidative phosphorylation as a novel target for the treatment of respiratory diseases, such as asthma.

Galectin 15 (LGALS15): A Gene Uniquely Expressed in the Uteri of Sheep and Goats that Functions in Trophoblast Attachment1

Galectins are a family of secreted animal lectins with biological roles in cell adhesion and migration. In sheep, galectin 15 (LGALS15) is expressed specifically in the endometrial luminal (LE) and superficial glandular (sGE) epithelia of the uterus in concert with blastocyst elongation during the peri-implantation period. The present study examined LGALS15 expression in the uterus of cattle, goats, and pigs. Although the bovine genome contains an LGALS15-like gene, expressed sequence tags encoding LGALS15 mRNA were found only for sheep, and full-length LGALS15 cDNAs were cloned only from endometrial total RNA isolated from pregnant sheep and goats, but not pregnant cattle or pigs. Ovine and caprine LGALS15 were highly homologous at the mRNA (95%) and protein (91%) levels, and all contained a conserved carbohydrate recognition domain and RGD recognition sequence for integrin binding. Endometrial LGALS15 mRNA levels increased after Day 11 of both the estrous cycle and pregnancy, and were considerably increased after Day 15 of pregnancy in goats. In situ hybridization detected abundant LGALS15 mRNA in endometrial LE and sGE of early pregnant goats, but not in cattle or pigs. Immunoreactive LGALS15 protein was present in endometrial epithelia and conceptus trophectoderm of goat uteri and detected within intracellular crystal structures in trophectoderm and LE. Recombinant ovine and caprine LGALS15 proteins elicited a dose-dependent increase in ovine trophectoderm cell attachment in vitro that was comparable to bovine fibronectin. These results support the hypothesis that LGALS15 is uniquely expressed in Caprinae endometria and functions as an attachment factor important for peri-implantation blastocyst elongation.

Galectin 15 (LGALS15) functions in trophectoderm migration and attachment

Galectin 15 (LGALS15) is expressed specifically by the endometrial luminal epithelium (LE) of the ovine uterus in concert with blastocyst growth, elongation, and implantation. LGALS15 contains a predicted carbohydrate recognition domain (CRD) as well as LDV and RGD recognition sequences for integrin binding. Studies tested the hypothesis that LGALS15 is a secreted regulator of blastocyst development, as well as growth, migration, adhesion, and apoptosis of trophoblast. Bovine embryos were produced in vitro by standard conditions, and putative zygotes were cultured in the presence of recombinant ovine LGALS15. Rates of embryo cleavage and blastocyst formation were not affected by LGALS15. LGALS15 moderately increased proliferation of ovine trophectoderm (oTr) cells. Staurosporine elicited apoptosis of oTr cells, which could be partially inhibited by LGALS15. Migration of oTr cells was stimulated by LGALS15 that was dependent on Jun N-terminal kinase (JNK). A dose-dependent increase in oTr cell attachment to LGALS15 was found that could be inhibited by cyclic GRGDS, but not GRADS, peptides. Mutation of the LDVRGD integrin binding sequence of LGALS15 to LADRAD decreased its ability to promote oTr cell attachment, whereas mutation of the CRD had little effect. LGALS15 induced formation of robust focal adhesions in oTr cells that was abolished by mutation of the LDVRGD sequence. Collectively, these results support the hypothesis that LGALS15 stimulates trophectoderm cell migration and attachment via integrin binding and activation which are critical to blastocyst elongation and implantation.

Discovery and characterization of an epithelial-specific galectin in the endometrium that forms crystals in the trophectoderm

Secretions of the uterus support survival and growth of the conceptus (embryo/fetus and associated membranes) during pregnancy. Galectin-15, also known as OVGAL11 and a previously uncharacterized member of the galectin family of secreted beta-galactoside lectins containing a conserved carbohydrate recognition domain and a separate putative integrin binding domain, was discovered in the uterus of sheep. In endometria of cyclic and pregnant sheep, galectin-15 mRNA was expressed specifically in the endometrial luminal epithelium but not in the conceptus. In pregnant sheep, galectin-15 mRNA expression appeared in the epithelia between days 10 and 12 and increased between days 12 and 16. Progesterone induced and IFN-tau stimulated galectin-15 mRNA in the endometrial epithelium. Galectin-15 protein was concentrated near and on the apical surface of the endometrial luminal epithelia and localized within discrete cytoplasmic crystalline structures of conceptus trophectoderm (Tr). In the uterine lumen, secreted galectin-15 protein increased between days 14 and 16 of pregnancy. Galectin-15 protein was functional in binding lactose and mannose sugars and immunologically identical to the unnamed Mr 14,000 (14K) protein from the ovine uterus that forms crystalline inclusion bodies in endometrial epithelia and conceptus Tr. Based on the functional studies of other galectins, galectin-15 is hypothesized to function extracellularly to regulate Tr migration and adhesion to the endometrial epithelium and intracellularly to regulate Tr cell survival, growth, and differentiation. Galectins may be useful as cellular and molecular markers for endometrial function and receptivity, to enhance conceptus survival and development, and to evaluate and enhance fertility.

Charcot-Leyden crystal protein (galectin-10) is not a dual function galectin with lysophospholipase activity but binds a lysophospholipase inhibitor in a novel structural fashion

Charcot-Leyden crystal (CLC) protein, initially reported to possess weak lysophospholipase activity, is still considered to be the eosinophil's lysophospholipase, but it shows no sequence similarities to any known lysophospholipases. In contrast, CLC protein has moderate sequence similarity, conserved genomic organization, and near structural identity to members of the galectin superfamily, and it has been designated galectin-10. To definitively determine whether or not CLC protein is a lysophospholipase, we reassessed its enzymatic activity in peripheral blood eosinophils and an eosinophil myelocyte cell line (AML14.3D10). Antibody affinity chromatography was used to fully deplete CLC protein from eosinophil lysates. The CLC-depleted lysates retained their full lysophospholipase activity, and this activity could be blocked by sulfhydryl group-reactive inhibitors, N-ethylmaleimide and p-chloromercuribenzenesulfonate, previously reported to inhibit the eosinophil enzyme. In contrast, the affinity-purified CLC protein lacked significant lysophospholipase activity. X-ray crystallographic structures of CLC protein in complex with the inhibitors showed that p-chloromercuribenzenesulfonate bound CLC protein via disulfide bonds with Cys(29) and with Cys(57) near the carbohydrate recognition domain (CRD), whereas N-ethylmaleimide bound to the galectin-10 CRD via ring stacking interactions with Trp(72), in a manner highly analogous to mannose binding to this CRD. Antibodies to rat pancreatic lysophospholipase identified a protein in eosinophil and AML14.3D10 cell lysates, comparable in size with human pancreatic lysophospholipase, which co-purifies in small quantities with CLC protein. Ligand blotting of human and murine eosinophil lysates with CLC protein as probe showed that it binds proteins also recognized by antibodies to pancreatic lysophospholipase. Our results definitively show that CLC protein is not one of the eosinophil's lysophospholipases but that it does interact with eosinophil lysophospholipases and known inhibitors of this lipolytic activity.

Charcot-Leyden crystals within a periapical lesion

Transmission electron microscopy revealed the presence of Charcot-Leyden crystals within a periapical lesion, which was assessed histopathologically as consistent with a periapical granuloma that failed to resolve after conventional endodontic treatment. This paper presents the clinical, radiographic, histological, and ultrastructural findings of this case and discusses their potential clinical significance.

Selective recognition of mannose by the human eosinophil Charcot-Leyden crystal protein (galectin-10): a crystallographic study at 1.8 A resolution

The role(s) of the eosinophil Charcot-Leyden crystal (CLC) protein in eosinophil or basophil function or associated inflammatory processes is yet to be established. Although the CLC protein has been reported to exhibit weak lysophospholipase activity, it shows virtually no sequence homology to any known member of this family of enzymes. The X-ray crystal structure of the CLC protein is very similar to the structure of the galectins, members of a beta-galactoside-specific animal lectin family, including a partially conserved galectin carbohydrate recognition domain (CRD). In the absence of any known natural carbohydrate ligand for this protein, the functional role of the CLC protein (galectin-10) has remained speculative. Here we describe structural studies on the carbohydrate binding properties of the CLC protein and report the first structure of a carbohydrate in complex with the protein. Interestingly, the CLC protein demonstrates no affinity for beta-galactosides and binds mannose in a manner very different from those of other related galectins that have been shown to bind lactosamine. The partial conservation of residues involved in carbohydrate binding led to significant changes in the topology and chemical nature of the CRD, and has implications for carbohydrate recognition by the CLC protein in vivo and its functional role in the biology of inflammation.

Cloning and expression of cDNA encoding rat liver 60-kDa lysophospholipase containing an asparaginase-like region and ankyrin repeat

Mammalian tissues contain small form and large form lysophospholipases. Here we report the cloning, sequence, and expression of cDNA encoding the latter form of lysophospholipase using antibody raised against the enzyme purified from rat liver supernatant (Sugimoto, H., and Yamashita, S. (1994) J. Biol. Chem. 269, 6252-6258). The 2,539-base pair cDNA encoded 564 amino acid residues with a calculated Mr of 60,794. The amino-terminal two-thirds of the deduced amino acid sequence significantly resembled Escherichia coli asparaginase I with the putative asparaginase catalytic triad Thr-Asp-Lys and was followed by leucine zipper motif. The carboxyl-terminal region carried ankyrin repeat. When the cDNA was transfected into HEK293 cells, not only lysophospholipase activity but also asparaginase and platelet-activating factor acetylhydrolase activities were expressed. Reverse transcription-polymerase chain reaction revealed that the transcript occurred at high levels in liver and kidney but was hardly detectable in lung and heart from which large form lysophospholipases had been purified, suggesting the presence of multiple forms of large form lysophospholipase in mammalian tissues.

Cell biology of the basophil

The cell biology of basophils, based on published studies spanning 1990-1997, is reviewed. These rarest cells of granulocyte lineages are now available in sufficient numbers for such studies to be done, based on new methods for isolating and purifying the cells from peripheral blood and organ sources and for their derivation in growth factor-containing cultures from their precursors de novo. These studies are dependent on electron microscopy for the accurate identification of basophils, studies which have recently established the presence of basophils in two new species--mice and monkeys. Secretory, endocytotic and storage properties of basophils constitute their mechanistic role(s) in human disease; their role(s) in health is, however, obscure. Development of immunoaffinity and enzyme-affinity ultrastructural labeling techniques to image the Charcot-Leyden crystal protein and histamine in human basophils, coupled with ultrastructural analysis of kinetic samples of cells obtained after stimulation with diverse secretogogues, has provided insight into the role of vesicles in secretory transport mechanisms in human basophils as well as the definition of key ultrastructural phenotypes of secreting basophils.

The genomic structure of the human Charcot-Leyden crystal protein gene is analogous to those of the galectin genes

The Charcot-Leyden crystal (CLC) protein, or eosinophil lysophospholipase, is a characteristic protein of human eosinophils and basophils; recent work has demonstrated that the CLC protein is both structurally and functionally related to the galectin family of beta-galactoside binding proteins. The galectins as a group share a number of features in common, including a linear ligand binding site encoded on a single exon. In this work, we demonstrate that the intron-exon structure of the gene encoding CLC is analogous to those encoding the galectins. The coding sequence of the CLC gene is divided into four exons, with the entire beta-galactoside binding site encoded by exon III. We have isolated CLC beta-galactoside binding sites from both orangutan (Pongo pygmaeus) and murine (Mus musculus) genomic DNAs, both encoded on single exons, and noted conservation of the amino acids shown to interact directly with the beta-galactoside ligand. The most likely interpretation of these results suggest the occurrence of one or more exon duplication and insertion events, resulting in the distribution of this lectin domain to CLC as well as to the multiple galectin genes.

Ultrastructural localization of Charcot-Leyden crystal protein in human eosinophils and basophils

The Charcot-Leyden crystal (CLC) protein with lysophospholipase activity and carbohydrate-binding properties is a characteristic constituent of eosinophils and basophils. We investigated its subcellular distribution using immunoelectron microscopy. Eosinophil progenitors, mature eosinophils and basophils all contained CLC protein in their cytosol and in the euchromatin of the nucleus. A minor population of granules in eosinophils, increasing in number with maturation, and a more abundant granule-population in basophils, were found to contain CLC protein. Double-labeling experiments showed, in eosinophils, that CLC protein-containing granules contain also eosinophil peroxidase, a characteristic specific granule protein. This suggests a relationship between the CLC protein-containing organelle and the specific granule. In basophils both the CLC protein positive and the negative granules showed the same characteristic particulate-like structure of the granular matrix and both share the same membrane marker CD63. In nasal polyps, macrophages were observed phagocytosing necrotic eosinophils. In these macrophages CLC protein-containing vesicles were observed, probably representing late endosomes. The dual (cytosolic/nuclear and granular) localization of CLC protein suggests that this protein enters both a secretory and a nonsecretory pathway during its biosynthesis, indicating functional roles for this protein both within the cell and extracellularly.

Eosinophil Charcot-Leyden crystal protein binds to beta-galactoside sugars

The Charcot-Leyden crystal protein (CLC) found in human eosinophils and basophils has 43-48% amino acid sequence similarity to the galectin family of beta-galactoside binding proteins. We show here that enzymatically active recombinant CLC binds to a lactose-conjugated agarose resin, and that binding is inhibited in a dose dependent fashion by both lactose (IC50 = 41 mM) and fucose (IC50 = 380 mM), but not by arabinose. These results demonstrate that CLC has functional as well as structural homology to the galectins, and suggest that CLC may also participate, as do the galectins, in mediating cell-cell and cell-matrix interactions, and in activating the cellular immune response.

Purification, cDNA cloning, and regulation of lysophospholipase from rat liver

A lysophospholipase was purified 506-fold from rat liver supernatant. The preparation gave a single 24-kDa protein band on SDS-polyacrylamide gel electrophoresis. The enzyme hydrolyzed lysophosphatidylcholine, lysophosphatidylethanolamine, lysophosphatidylinositol, lysophosphatidylserine, and 1-oleoyl-2-acetyl-sn-glycero-3-phosphocholine at pH 6-8. The purified enzyme was used for the preparation of antibody and peptide sequencing. A cDNA clone was isolated by screening a rat liver lambda gt11 cDNA library with the antibody, followed by the selection of further extended clones from a lambda gt10 library. The isolated cDNA was 2,362 base pairs in length and contained an open reading frame encoding 230 amino acids with a Mr of 24,708. The peptide sequences determined were found in the reading frame. When the cDNA was expressed in Escherichia coli cells as the beta-galactosidase fusion, lysophosphatidylcholine-hydrolyzing activity was markedly increased. The deduced amino acid sequence showed significant similarity to Pseudomonas fluorescence esterase A and Spirulina platensis esterase. The three sequences contained the GXSXG consensus at similar positions. The transcript was found in various tissues with the following order of abundance: spleen, heart, kidney, brain, lung, stomach, and testis = liver. In contrast, the enzyme protein was abundant in the following order: testis, liver, kidney, heart, stomach, lung, brain, and spleen. Thus the mRNA abundance disagreed with the level of the enzyme protein in liver, testis, and spleen. When HL-60 cells were induced to differentiate into granulocytes with dimethyl sulfoxide, the 24-kDa lysophospholipase protein increased significantly, but the mRNA abundance remained essentially unchanged. Thus a posttranscriptional control mechanism is present for the regulation of 24-kDa lysophospholipase.

Crystal structure of human Charcot-Leyden crystal protein, an eosinophil lysophospholipase, identifies it as a new member of the carbohydrate-binding family of galectins

BACKGROUND

The Charcot-Leyden crystal (CLC) protein is a major autocrystallizing constituent of human eosinophils and basophils, comprising approximately 10% of the total cellular protein in these granulocytes. Identification of the distinctive hexagonal bipyramidal crystals of CLC protein in body fluids and secretions has long been considered a hallmark of eosinophil-associated allergic inflammation. Although CLC protein possesses lysophospholipase activity, its role(s) in eosinophil or basophil function or associated inflammatory responses has remained speculative.

RESULTS

The crystal structure of the CLC protein has been determined at 1.8 A resolution using X-ray crystallography. The overall structural fold of CLC protein is highly similar to that of galectins -1 and -2, members of an animal lectin family formerly classified as S-type or S-Lac (soluble lactose-binding) lectins. This is the first structure of an eosinophil protein to be determined and the highest resolution structure so far determined for any member of the galectin family.

CONCLUSIONS

The CLC protein structure possesses a carbohydrate-recognition domain comprising most, but not all, of the carbohydrate-binding residues that are conserved among the galectins. The protein exhibits specific (albeit weak) carbohydrate-binding activity for simple saccharides including N-acetyl-D-glucosamine and lactose. Despite CLC protein having no significant sequence or structural similarities to other lysophospholipase catalytic triad has also been identified within the CLC structure, making it a unique dual-function polypeptide. These structural findings suggest a potential intracellular and/or extracellular role(s) for the galectin-associated activities of CLC protein in eosinophil and basophil function in allergic diseases and inflammation.

Characteristics of lysophospholipase activity expressed by cytosolic phospholipase A2

Evidence has accumulated to suggest that a wide variety of mammalian cells and tissues express a cytosolic phospholipase A2 with arachidonoyl preference (cPLA2). Purified rabbit platelet-derived cPLA2, as well as the human recombinant enzyme originally identified in the monocytic leukemic cell line U937, exhibit significant lysophospholipase activity. Several series of experiments indicated that a single protein mediated both activities. Treatment of the purified enzyme with p-bromophenacylbromide or an anti-(rabbit platelet cPLA2) monoclonal antibody, RHY-5, suppressed the activity of phospholipase A2 without any appreciable effect on lysophospholipase activity, suggesting that the domain(s) required for phospholipase A2 activity may be located separately from that for lysophospholipase activity. Lysophospholipase activity was appreciably detected above the critical micellar concentration of the substrate. Lysophosphatidylcholine was also hydrolyzed efficiently when it was incorporated into liposomes made of dialkylphosphatidylcholine. The hydrolysis of lysophospholipid was dependent on the fatty acid bound at the sn1 position; the relative rates of hydrolysis of 1-oleoyllysophosphatidylcholine, 1-palmitoyllysophosphatidylcholine, and 1-stearoyllysophosphatidylcholine were 23, 8, and 1, respectively. A similar order of reactivity was observed with lysophospholipid incorporated into dialkylphosphatidylcholine liposomes. cPLA2 may function not only as an arachidonate liberation enzyme but also as an enzyme responsible for degradation of certain molecular species of lysophospholipids formed in membranes.

Isolation and characterization of three lysophospholipases from the murine macrophage cell line WEHI 265.1

Anion exchange chromatography of WEHI 265.1 cell homogenates resolved the lysophospholipase activity into three peaks, when assayed using lysophosphatidylcholine as a substrate. Peaks 1 and 2 were purified by sequential hydrophobic interaction and gel filtration chromatography. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis of the purified peaks 1 and 2 indicated homogeneous proteins with apparent masses of 28 and 27 kDa, respectively. Peak 3 lysophospholipases was partially purified by hydrophobic, hydroxyapatite and gel filtration chromatography. Peak 3 lysophospholipase also had calcium-dependent phospholipase A2 activity, which further co-purified with the lysophospholipase activity. The three lysophospholipases were characterized with respect to substrate specificity, additional enzymatic activities and the effects of lipids, metal ions and other compounds on enzymatic activity. Peaks 1, 2 and 3 hydrolyzed lysophosphatidylcholine most readily, but lysophosphatidylethanolamine also served as substrate for each enzyme. Furthermore, all three enzymes hydrolyzed platelet activating factor and acetylated lysophosphatidylcholine. Each lysophospholipase was inhibited by free fatty acids and by palmitoyl carnitine, although the relative sensitivities to these agents differed among the enzymes. The lysophospholipase activities of peaks 1 and 2, but not peak 3, were inhibited by phenylmethylsulfonyl fluoride, diisopropyl fluorophosphate and N-ethylmaleimide. Although they had similar masses, the amino acid compositions of peaks 1 and 2 differed, indicating that these are distinct proteins rather than posttranslational modifications of the same gene product.

Possible influence of lysophospholipase on the production of 1-acyl-2-acetylglycerophosphocholine in macrophages

The rate of production of 1-O-alkyl-2-acetyl-sn-glycero-3-phosphocholine (PAF) and 1-acyl-2-acetyl-sn-glycero-3-phosphocholine (acylPAF) was measured in macrophages following the incorporation of [3H]acetate. Upon activation by A23187, guinea pig alveolar macrophages incorporated [3H]acetate into PAF, but a little radioactivity was found in acylPAF. However, labeling of acylPAF and PAF with [3H]acetate was greatly enhanced in A23187-stimulated alveolar macrophages that had been pretreated with phenylmethanesulphonyl fluoride (PMSF). [3H]PAF was predominantly converted to 1-[3H]alkyl-2-acyl glycerophosphocholine, but [14C]acylPAF rapidly hydrolyzed to 14C-labeled free fatty acid by the incubation with lysates prepared from macrophages. The deacetylation of [14C]acylPAF and [3H]PAF by acetylhydrolase and also the hydrolysis of [14C]lysoPC by lysophospholipase were strongly inhibited in macrophages that had been pretreated with PMSF, while PMSF failed to inhibit the activities of acetyltransferase and acyltransferase. The relative proportions of PAF and acylPAF were quite different in different types of cells. In contrast to alveolar macrophages, peritoneal macrophages, neutrophils and spleen cells from guinea pigs incorporated 2-4 times more [3H]acetate into acylPAF than into PAF. The presence of high levels of acylPAF in peritoneal macrophages was confirmed by GLC-MS analysis. The activities of lysophospholipase, acetylhydrolase and acetyltransferase were measured in alveolar and peritoneal macrophages to determine whether the preferential formation of acylPAF as compared to PAF in peritoneal macrophages was due to differences in these activities between alveolar and peritoneal macrophages. The activity of acetylhydrolase of peritoneal macrophages was almost the same as that in alveolar macrophages. The activity of acetyltransferase in peritoneal macrophages was about half of that in alveolar macrophages. However, the activity of lysophospholipase in peritoneal macrophages was one-sixth of that in alveolar macrophages. These results suggest that lysophospholipase is one of the primary factors involved in the control of the production of acylPAF in activated cells, and that it acts by modulating the availability of lysoPC for the synthesis of acylPAF. Furthermore, high levels of activity of lysophospholipase allow the preferential formation of PAF, via the rapid hydrolysis of lysoPC which would act as a competitive inhibitor of the incorporation of acetate into lysoPAF.

The catabolism of exogenous lysophosphatidylcholine in isolated perfused rat and guinea pig hearts: a comparative study

Lysophosphatidylcholine (lysoPC) is an arrhythmogenic phospholipid metabolite which accumulates in the ischemic myocardium. Reduced catabolism of lysoPC has been proposed to be one of the biochemical mechanisms responsible for the increase in lysoPC content. In this investigation we compared the microsomal catabolism of exogenous labeled lysoPC in isolated perfused rat and guinea pig hearts. Analysis of the amount of radioactivity in microsomal phosphatidylcholine (PC) and free fatty acid (FFA) was used as an index of the participation in lysoPC clearance by acylation catalyzed by acyl-CoA:lysoPC acyltransferase and deacylation catalyzed by lysophospholipase, respectively. There was no significant difference in the incorporation of radioactivity into rat and guinea pig heart microsomes; however, the patterns of radioactivity in lysoPC metabolites were notably different. Equal participation by deacylation and reacylation was observed in rat microsomes, whereas deacylation was clearly the preferred route for lysoPC clearance in guinea pig microsomes. Modulation of enzyme activity by treatment of the isolated heart with pHMB, a sulfhydryl agent, was used to probe the relationship among acylation, deacylation and the extent of lysoPC clearance. In guinea pig microsomes impairment of lysoPC acylation was not associated with any change in the amount of radioactivity in lysoPC because of a compensatory increase in deacylation. In contrast, impaired deacylation in rat microsomes led to significant elevations in the amount of radioactivity in lysoPC. We conclude, therefore, that in intact perfused rat and guinea pig hearts the relative participation of acylation and deacylation in lysoPC clearance differs. Moreover, we propose that the level of deacylation by lysophospholipase is an important factor in the extent of clearance of lysoPC.

A current perspective on the role of eosinophils in dermatologic diseases

Eosinophils are frequently observed in cutaneous inflammation, but little is known of their significance in the pathophysiology of cutaneous disease. Recent studies of the structure, content, and activities of the eosinophil have shown that it has potent toxic proteins with the potential to mediate tissue damage. Furthermore, immunofluorescent localization of eosinophil granule proteins has shown that eosinophils disrupt in tissue and deposit toxic granule proteins. The deposition of granule proteins in several diseases is vastly out proportion to the number of identifiable cells and indicates that eosinophil involvement in cutaneous disease cannot be judged by the number of intact eosinophils in the tissue. Specifically, deposition of eosinophil granule proteins outside of eosinophils has been observed in eczematous lichenified disorders with elevated serum levels of immunoglobulin E, in urticarial and angioedematous disorders, and in bullous diseases. The structural, compositional, and functional characteristics of eosinophils are reviewed, and evidence of eosinophil degranulation in cutaneous diseases is presented. Mechanisms whereby eosinophil degranulation may mediate pathophysiologic effects are also discussed.

Lysophospholipase activity of Ascaris suum-induced mouse peritoneal neutrophils and eosinophils

Lysophospholipase activity of mouse peritoneal neutrophils and eosinophils was studied to determine if neutrophils and eosinophils have lysophospholipase activity when treated with Ascaris suum whole worm extract, if zymosan activated complement can induce increased lysophospholipase activity, or if the immune status of the host has an effect on lysophospholipase activity. Neutrophils from noninfected or infected (immunized) mice were found to have increased lysophospholipase activity when treated with A. suum whole worm extract or zymosan activated complement demonstrating neutrophils as a source of lysophospholipase activity in the presence or absence of an immune response. Eosinophils from immunized mice had increased lysophospholipase activity when treated with either A. suum whole worm extract or zymosan activated complement.