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      Structural study of biologically significant ligands with major birch pollen allergen Betv1 by docking and molecular dynamics simulation

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          Abstract

          The major birch pollen allergen, Betv1 of Betula verrucosa is the main causative agent of birch pollen allergy in humans. Betv1 is capable of binding several physiological ligands including fatty acids, flavones, cytokinins and sterols. Until now, no structural information from crystallography or NMR is available regarding binding mode of any of these ligands into the binding pocket of Betv1. In the present study thirteen ligands have been successfully docked into the hydrophobic cavity of Betv1 and binding free energies of the complexes have been calculated using AutoDock 3.0.5. A linear relationship with correlation coefficient (R 2) of 0.6 is obtained between ΔG bs values plotted against their corresponding IC50 values. The complex formed between Betv1 and the best docking pose for each ligand has been optimized by molecular dynamics simulation. Here, we describe the ligand binding of Betv1, which provides insight into the biological function of this protein. This knowledge is required for structural alteration or inhibition of some of these ligands in order to modify the allergenic properties of this protein.

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          Most cited references16

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          Biochemical complementation of chalcone synthase mutants defines a role for flavonols in functional pollen.

          Chalcone synthase catalyzes the initial step of that branch of the phenylpropanoid pathway that leads to flavonoids. A lack of chalcone synthase activity has a pleiotropic effect in maize and petunia mutants: pollen fertility as well as flavonoid synthesis is disrupted. Both maize and petunia mutants are self-sterile due to a failure to produce a functional pollen tube. The finding that the mutant pollen is partially functional on wild-type stigmas led to the isolation and identification of kaempferol as a pollen germination-inducing constituent in wild-type petunia stigma extracts. We show that adding micromolar quantities of kaempferol to the germination medium or to the stigma at pollination is sufficient to restore normal pollen germination and tube growth in vitro and full seed set in vivo. Further we show that the rescue ability resides in particular structural features of a single class of compounds, the flavonol aglycones. This finding identifies another constituent of plant reproduction and suggests that addition or removal of the flavonol signal during pollen germination and tube growth provides a feasible way to control plant fertility.
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            The major birch allergen, Bet v 1, shows affinity for a broad spectrum of physiological ligands.

            Bet v 1 is a 17-kDa protein abundantly present in the pollen of the White birch tree and is the primary cause of birch pollen allergy in humans. Its three-dimensional structure is remarkable in that a solvent-accessible cavity traverses the core of the molecule. The biological function of Bet v 1 is unknown, although it is homologous to a family of pathogenesis-related proteins in plants. In this study we first show that Bet v 1 in the native state is able to bind the fluorescent probe 8-anilino-1-naphthalenesulfonic acid (ANS). ANS binds to Bet v 1 with 1:1 stoichiometry, and NMR data indicate that binding takes place in the cavity. Using an ANS displacement assay, we then identify a range of physiologically relevant ligands, including fatty acids, flavonoids, and cytokinins, which generally bind with low micromolar affinity. The ability of these ligands to displace ANS suggests that they also bind in the cavity, although the exact binding sites seem to vary among different ligands. The cytokinins, for example, seem to bind at a separate site close to ANS, because they increase the fluorescence of the ANS. Bet v 1 complex. Also, the fluorescent sterol dehydroergosterol binds to Bet v 1 as demonstrated by direct titrations. This study provides the first qualitative and quantitative data on the ligand binding properties of this important pollen allergen. Our findings indicate that ligand binding is important for the biological function of Bet v 1.
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              The gene coding for the major birch pollen allergen Betv1, is highly homologous to a pea disease resistance response gene.

              Pollen of the white birch (Betula verrucosa) is one of the main causes of Type I allergic reactions (allergic rhinoconjunctivitis, allergic bronchial asthma) in Middle and Northern Europe, North America and the USSR. Type I allergies are a major threat to public health in these countries, since 10-15% of the population suffer from these diseases. BetvI, an allergenic protein with an Mr of 17 kd is a constituent of the pollen of white birch and is responsible for IgE binding in more than 95% of birch pollen allergic patients. Here, we report the complete nucleotide sequence and deduced amino acid sequence of a cDNA clone coding for the major pollen allergen (BetvI) of white birch. It is similar to the N-terminal peptide sequences of the allergens of hazel, alder and hornbeam (close relatives) but it has no significant sequence homology to any other known allergens. However, it shows 55% sequence identity with a pea disease resistance response gene, indicating that BetvI may be involved in pathogen resistance of pollen.
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                Author and article information

                Journal
                Bioinformation
                Bioinformation
                Bioinformation
                Biomedical Informatics Publishing Group
                0973-2063
                2010
                24 January 2010
                : 4
                : 7
                : 326-330
                Affiliations
                Debjani Roy Bioinformatics Centre, Bose Institute, Acharya J.C Bose Centenary Building, P-1/12 C.I.T Scheme –VII M, Kolkata – 700054 India
                Author notes
                [* ]Debjani Roy: debjani@ 123456bic.boseinst.ernet.in Tel: +91-33-2355-6626; +91-33-2355-2816; Fax: +91-33-2355-3886
                Article
                006900042010
                2957764
                20978606
                831834a9-f87c-4f16-a056-398d5c51471f
                © 2010 Biomedical Informatics Publishing Group

                This is an open-access article, which permits unrestricted use, distribution, and reproduction in any medium, for non-commercial purposes, provided the original author and source are credited.

                History
                : 20 October 2009
                : 24 November 2009
                Categories
                Hypothesis

                Bioinformatics & Computational biology
                birch pollen allergy,betula verrucosa,molecular dynamics simulation,docking

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