Structure of the Fungal Beta-Glucan-Binding Immune Receptor Dectin-1: Implications for Function.
TL;DR: Several dectin‐1 crystal structures are reported, including a high‐resolution structure and a 2.8 Å resolution structure in which a short soaked natural β‐glucan is trapped in the crystal lattice, which suggest potential mechanisms of defense against fungal pathogens.
Abstract: The murine molecule dectin-1 (known as the β-glucan receptor in humans) is an immune cell surface receptor implicated in the immunological defense against fungal pathogens. Sequence analysis has indicated that the dectin-1 extracellular domain is a C-type lectin-like domain, and functional studies have established that it binds fungal β-glucans. We report several dectin-1 crystal structures, including a high-resolution structure and a 2.8 A resolution structure in which a short soaked natural β-glucan is trapped in the crystal lattice. In vitro characterization of dectin-1 in the presence of its natural ligand indicates higher-order complex formation between dectin-1 and β-glucans. These combined structural and biophysical data considerably extend the current knowledge of dectin-1 structure and function, and suggest potential mechanisms of defense against fungal pathogens.
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TL;DR: This review explores what is currently known about β‐glucan recognition and how this recognition stimulates immune responses, and special emphasis is placed on Dectin‐1, as the authors know the most about how this key β‐ glucan receptor translates recognition into intracellular signaling, stimulates cellular responses,and participates in orchestrating the adaptive immune response.
Abstract: Beta-glucans are recognized by the innate immune system. This recognition plays important roles in host defense and presents specific opportunities for clinical modulation of the host immune response. Neutrophils, macrophages, and dendritic cells among others express several receptors capable of recognizing beta-glucan in its various forms. This review explores what is currently known about beta-glucan recognition and how this recognition stimulates immune responses. Special emphasis is placed on Dectin-1, as we know the most about how this key beta-glucan receptor translates recognition into intracellular signaling, stimulates cellular responses, and participates in orchestrating the adaptive immune response.
515 citations
Cites background from "Structure of the Fungal Beta-Glucan..."
...The crystal structure of the lectin domain suggested that while individual Dectin-1 molecules can bind b-glucans, cooperative binding as dimers may be more efficient (33)....
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TL;DR: Mincle, a C-type lectin, is expressed predominantly on macrophages, and is here shown to play a role in macrophage responses to the yeast Candida albicans.
Abstract: The recognition of carbohydrate moieties by cells of the innate immune system is emerging as an essential element in antifungal immunity, but despite the number and diversity of lectins expressed by innate immune cells, few carbohydrate receptors have been characterized. Mincle, a C-type lectin, is expressed predominantly on macrophages, and is here shown to play a role in macrophage responses to the yeast Candida albicans. After exposure to the yeast in vitro, Mincle localized to the phagocytic cup, but it was not essential for phagocytosis. In the absence of Mincle, production of TNF-alpha by macrophages was reduced, both in vivo and in vitro. In addition, mice lacking Mincle showed a significantly increased susceptibility to systemic candidiasis. Thus, Mincle plays a novel and nonredundant role in the induction of inflammatory signaling in response to C. albicans infection.
387 citations
Cites background or methods from "Structure of the Fungal Beta-Glucan..."
...Briefly, Mincle protein was found to be insoluble, so it was refolded as previously described for the C-type lectin Dectin-1, using a dilution protocol (15, 28)....
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...signaling cascade via spleen tyrosine kinase (14, 15)....
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01 Jan 2008
TL;DR: In this paper, the c-type lectin Mincle was observed to localise in the phagocytic cup of macrophages in response to a range of stimuli.
Abstract: The recognition of carbohydrate moieties by cells of the innate immune system is emerging as an essential element in anti-fungal immunity, but few carbohydrate receptors have been characterised, despite the number and diversity of lectins expressed by innate immune cells. We demonstrate a novel role for the c-type lectin Mincle in macrophage responses to C. albicans. Mincle was observed to localise in the phagocytic cup of macrophages in response to a range of stimuli. Loss of Mincle reduced macrophage TNF production both in vivo and in vitro, but did not alter the number of Candida yeast phagocytised. Mice lacking Mincle showed a significantly increased susceptibility to systemic candidiasis. Thus Mincle contributes a novel and non-redundant role in the induction of inflammatory signalling in response to C. albicans infection.
358 citations
TL;DR: A comprehensive understanding of the interactions between the host membrane receptors and the fungal cell wall components is still lacking and thefungal adhesins playing a role in adhesion to host have been only explored in yeasts.
Abstract: The search for common host mechanisms that recognize human fungal pathogens as non-self has led to an increased interest in cell wall polysaccharides since they are absent from mammals and at least for some of them, common to all fungal species. Even though the receptors recognizing mannans and beta-1,3-glucans have been extensively studied to date, the epitope of the polysaccharide ligand is often not well defined. In addition, receptors recognizing other cell wall major components such as chitin, alpha-1,3-glucan or galactose polymers remain to be identified. Moreover, the fungal adhesins playing a role in adhesion to host have been only explored in yeasts. Eventhough progresses have been made in the last 10 years, a comprehensive understanding of the interactions between the host membrane receptors and the fungal cell wall components is still lacking.
266 citations
Cites background from "Structure of the Fungal Beta-Glucan..."
...The recent analysis of the Dectin-1 crystal structure (Brown et al., 2007) confirmed that the conformation does not resemble the one seen in classical calcium-dependent carbohydrate binding C-type lectinlike domains....
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...crystal structure (Brown et al., 2007) confirmed that the...
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TL;DR: This study examined the effect of glucan structure on recognition and binding by murine recombinant Dectin-1 with a library of natural product and synthetic (1→3)-β/(1→6)-β-glucans as well as nonglucan polymers and found that glucan derived from a saprophytic yeast was recognized with higher affinity than glucanderived from the pathogen Candida albicans.
Abstract: Glucans are structurally diverse fungal biopolymers that stimulate innate immunity and are fungal pathogen-associated molecular patterns. Dectin-1 is a C-type lectin-like pattern recognition receptor that binds glucans and induces innate immune responses to fungal pathogens. We examined the effect of glucan structure on recognition and binding by murine recombinant Dectin-1 with a library of natural product and synthetic (1-->3)-beta/(1-->6)-beta-glucans as well as nonglucan polymers. Dectin-1 is highly specific for glucans with a pure (1-->3)-beta-linked backbone structure. Although Dectin-1 is highly specific for (1-->3)-beta-d-glucans, it does not recognize all glucans equally. Dectin-1 differentially interacted with (1-->3)-beta-d-glucans over a very wide range of binding affinities (2.6 mM-2.2 pM). One of the most striking observations that emerged from this study was the remarkable high-affinity interaction of Dectin-1 with certain glucans (2.2 pM). These data also demonstrated that synthetic glucan ligands interact with Dectin-1 and that binding affinity increased in synthetic glucans containing a single glucose side-chain branch. We also observed differential recognition of glucans derived from saprophytes and pathogens. We found that glucan derived from a saprophytic yeast was recognized with higher affinity than glucan derived from the pathogen Candida albicans. Structural analysis demonstrated that glucan backbone chain length and (1-->6)-beta side-chain branching strongly influenced Dectin-1 binding affinity. These data demonstrate: 1) the specificity of Dectin-1 for glucans; 2) that Dectin-1 differentiates between glucan ligands based on structural determinants; and 3) that Dectin-1 can recognize and interact with both natural product and synthetic glucan ligands.
248 citations
Cites background from "Structure of the Fungal Beta-Glucan..."
...Adachi et al. (2004) have identified Trp221 and His223 as critical for the interaction of -glucans with Dectin-1....
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...In a recent study, Brown et al. (2007) have elucidated the crystal structure of Dectin-1....
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...We speculate that the helical nature of glucan polymers may facilitate the interaction of glucans with the Trp221/His223 groove in Dectin-1 (Adachi et al., 2004)....
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...Our results suggest that (133)- -D-glucans with a polymer backbone composed of seven or more glucose repeat subunits can interact with the Trp221/His223 groove in Dectin-1....
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...Their model revealed a shallow groove running between Trp221 and His223 (Brown et al., 2007)....
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References
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TL;DR: The methods presented in the chapter have been applied to solve a large variety of problems, from inorganic molecules with 5 A unit cell to rotavirus of 700 A diameters crystallized in 700 × 1000 × 1400 A cell.
Abstract: Publisher Summary X-ray data can be collected with zero-, one-, and two-dimensional detectors, zero-dimensional (single counter) being the simplest and two-dimensional the most efficient in terms of measuring diffracted X-rays in all directions. To analyze the single-crystal diffraction data collected with these detectors, several computer programs have been developed. Two-dimensional detectors and related software are now predominantly used to measure and integrate diffraction from single crystals of biological macromolecules. Macromolecular crystallography is an iterative process. To monitor the progress, the HKL package provides two tools: (1) statistics, both weighted (χ2) and unweighted (R-merge), where the Bayesian reasoning and multicomponent error model helps obtain proper error estimates and (2) visualization of the process, which helps an operator to confirm that the process of data reduction, including the resulting statistics, is correct and allows the evaluation of the problems for which there are no good statistical criteria. Visualization also provides confidence that the point of diminishing returns in data collection and reduction has been reached. At that point, the effort should be directed to solving the structure. The methods presented in the chapter have been applied to solve a large variety of problems, from inorganic molecules with 5 A unit cell to rotavirus of 700 A diameters crystallized in 700 × 1000 × 1400 A cell.
31,667 citations
TL;DR: CCP4mg is a project that aims to provide a general-purpose tool for structural biologists, providing tools for X-ray structure solution, structure comparison and analysis, and publication-quality graphics.
Abstract: CCP4mg is a project that aims to provide a general-purpose tool for structural biologists, providing tools for X-ray structure solution, structure comparison and analysis, and publication-quality graphics. The map-fitting tools are available as a stand-alone package, distributed as `Coot'.
27,505 citations
"Structure of the Fungal Beta-Glucan..." refers methods in this paper
...Crystallographic refinement used CNS (Brünger et al. 1998) and REFMAC5 (Murshudov et al. 1997), with O (Jones et al. 1991) and Coot (Emsley and Cowtan 2004) used for manual checking and building with reference to 2Fo-Fc and Fo-Fc electron density maps....
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...1991) and Coot (Emsley and Cowtan 2004) used for manual checking and building with reference to 2Fo-Fc and Fo-Fc electron density maps....
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TL;DR: The Crystallography & NMR System (CNS) as mentioned in this paper is a software suite for macromolecular structure determination by X-ray crystallography or solution nuclear magnetic resonance (NMR) spectroscopy.
Abstract: A new software suite, called Crystallography & NMR System (CNS), has been developed for macromolecular structure determination by X-ray crystallography or solution nuclear magnetic resonance (NMR) spectroscopy. In contrast to existing structure-determination programs the architecture of CNS is highly flexible, allowing for extension to other structure-determination methods, such as electron microscopy and solid-state NMR spectroscopy. CNS has a hierarchical structure: a high-level hypertext markup language (HTML) user interface, task-oriented user input files, module files, a symbolic structure-determination language (CNS language), and low-level source code. Each layer is accessible to the user. The novice user may just use the HTML interface, while the more advanced user may use any of the other layers. The source code will be distributed, thus source-code modification is possible. The CNS language is sufficiently powerful and flexible that many new algorithms can be easily implemented in the CNS language without changes to the source code. The CNS language allows the user to perform operations on data structures, such as structure factors, electron-density maps, and atomic properties. The power of the CNS language has been demonstrated by the implementation of a comprehensive set of crystallographic procedures for phasing, density modification and refinement. User-friendly task-oriented input files are available for nearly all aspects of macromolecular structure determination by X-ray crystallography and solution NMR.
15,182 citations
TL;DR: The likelihood function for macromolecular structures is extended to include prior phase information and experimental standard uncertainties and the results derived are consistently better than those obtained from least-squares refinement.
Abstract: This paper reviews the mathematical basis of maximum likelihood The likelihood function for macromolecular structures is extended to include prior phase information and experimental standard uncertainties The assumption that different parts of a structure might have different errors is considered A method for estimating σA using `free' reflections is described and its effects analysed The derived equations have been implemented in the program REFMAC This has been tested on several proteins at different stages of refinement (bacterial α-amylase, cytochrome c′, cross-linked insulin and oligopeptide binding protein) The results derived using the maximum-likelihood residual are consistently better than those obtained from least-squares refinement
14,622 citations
"Structure of the Fungal Beta-Glucan..." refers methods in this paper
...Crystallographic refinement used CNS (Brünger et al. 1998) and REFMAC5 (Murshudov et al. 1997), with O (Jones et al. 1991) and Coot (Emsley and Cowtan 2004) used for manual checking and building with reference to 2Fo-Fc and Fo-Fc electron density maps....
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...1998) and REFMAC5 (Murshudov et al. 1997), with O (Jones et al....
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TL;DR: The MOLSCRIPT program as discussed by the authors produces plots of protein structures using several different kinds of representations, including simple wire models, ball-and-stick models, CPK models and text labels.
Abstract: The MOLSCRIPT program produces plots of protein structures using several different kinds of representations. Schematic drawings, simple wire models, ball-and-stick models, CPK models and text labels can be mixed freely. The schematic drawings are shaded to improve the illusion of three dimensionality. A number of parameters affecting various aspects of the objects drawn can be changed by the user. The output from the program is in PostScript format.
13,971 citations
"Structure of the Fungal Beta-Glucan..." refers methods in this paper
...Figures were produced using Bobscript (Esnouf 1999) and MolScript (Kraulis 1991)....
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