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Dolores Solís - One of the best experts on this subject based on the ideXlab platform.

  • ab type lectin toxin agglutinin from mistletoe differences in affinity of the two galactoside binding trp tyr sites and regulation of their functionality by monomer dimer equilibrium
    Glycobiology, 2006
    Co-Authors: M.a. Jimenez, Sabine André, Hans-c. Siebert, Hans-j. Gabius, Dolores Solís
    Abstract:

    Viscumin of mistletoe (Viscum album L.) has a concentrationdependent activity profile unique to plant AB-toxins. It starts with lectin-dependent mitogenicity and then covers toxicity and cell agglutination, associated with shifts in the monomer/ dimer equilibrium. Each lectin subunit harbors two sections for ligand contact. In the dimer, the B-chain sites in subdomain 2g (designated as the Tyr-sites) appear fully accessible, whereas Trp-sites in subdomain 1a are close to the dimer interface. It is unclear whether both types of sites operate similarly in binding glycoligands in solution. By systematically covering a broad range of lactose/lectin ratio in isothermal titration calorimetry, we obtained evidence for two sites showing dissimilar binding affinity. Intriguingly, the site with higher affinity was only partially occupied. To assign the observed properties to the Trp/ Tyr-sites, we next performed chemically induced dynamic nuclear polarization measurements of Trp and Tyr accessibility. A Tyr signal, but not distinct Trp peaks, was recorded when testing the dimer. Lactose-quenchable Trp peaks became visible on the destabilization of the dimer by citraconylation, intimating Trp involvement in ligand contact in the monomer. Fittingly, Tyr acetylation but not mild Trp oxidation reduced the dimer hemagglutination activity and the extent of binding to asialofetuin–Sepharose 4B. Altogether, the results attribute lectin activity in the dimer primarily to Tyr-sites. Full access to Trp-sites is gained on dimer dissociation. Thus, the monomer/ dimer equilibrium of viscumin regulates the operativity of these sites. Their structural divergence affords the possibility for differences in ligand selection when comparing monomers (Tyr- and Trp-sites) with dimers (primarily Tyr-sites).

  • AB-type lectin (toxin/agglutinin) from mistletoe: differences in affinity of the two galactoside-binding Trp/Tyr-sites and regulation of their functionality by monomer/dimer equilibrium
    Glycobiology, 2006
    Co-Authors: M.a. Jimenez, Sabine André, Hans-c. Siebert, Hans-j. Gabius, Dolores Solís
    Abstract:

    Viscumin of mistletoe (Viscum album L.) has a concentrationdependent activity profile unique to plant AB-toxins. It starts with lectin-dependent mitogenicity and then covers toxicity and cell agglutination, associated with shifts in the monomer/ dimer equilibrium. Each lectin subunit harbors two sections for ligand contact. In the dimer, the B-chain sites in subdomain 2g (designated as the Tyr-sites) appear fully accessible, whereas Trp-sites in subdomain 1a are close to the dimer interface. It is unclear whether both types of sites operate similarly in binding glycoligands in solution. By systematically covering a broad range of lactose/lectin ratio in isothermal titration calorimetry, we obtained evidence for two sites showing dissimilar binding affinity. Intriguingly, the site with higher affinity was only partially occupied. To assign the observed properties to the Trp/ Tyr-sites, we next performed chemically induced dynamic nuclear polarization measurements of Trp and Tyr accessibility. A Tyr signal, but not distinct Trp peaks, was recorded when testing the dimer. Lactose-quenchable Trp peaks became visible on the destabilization of the dimer by citraconylation, intimating Trp involvement in ligand contact in the monomer. Fittingly, Tyr acetylation but not mild Trp oxidation reduced the dimer hemagglutination activity and the extent of binding to asialofetuin–Sepharose 4B. Altogether, the results attribute lectin activity in the dimer primarily to Tyr-sites. Full access to Trp-sites is gained on dimer dissociation. Thus, the monomer/ dimer equilibrium of viscumin regulates the operativity of these sites. Their structural divergence affords the possibility for differences in ligand selection when comparing monomers (Tyr- and Trp-sites) with dimers (primarily Tyr-sites).

Timothy A. Keiderling - One of the best experts on this subject based on the ideXlab platform.

  • Geometry and Efficacy of Cross-Strand Trp/Trp, Trp/Tyr, and Tyr/Tyr Aromatic Interaction in a β-Hairpin Peptide
    Biochemistry, 2010
    Co-Authors: Dan Mcelheny, Takahiro Takekiyo, Timothy A. Keiderling
    Abstract:

    The Trpzip2 peptide (WTWENGKWTWK-NH(2)), designed by Cochran and co-workers, contains two pairs of Trp's having cross-strand interaction and forms a stable antiparallel beta-hairpin. In order to study the geometries and effects on the structure and stability of different aromatic interactions, selected tryptophan residues were substituted with Tyr to get three Trpzip2 mutants with different Trp/Trp, Trp/Tyr, and Tyr/Tyr interacting pairs. Their native-state structures were determined using two-dimensional (2D) NMR and shown to have the same cross-strand edge-to-face Trp/Trp interaction as that in Trpzip2 for the Trp/Trp pair. The analogous Trp/Tyr and Tyr/Tyr pairs also tended to have an edge-to-face geometry. The effects of specific Trp/Trp, Trp/Tyr, and Tyr/Tyr interactions on hairpin stability were studied by varying temperature and monitoring structure with electronic circular dichroism (CD) and infrared (IR) absorption spectra. IR and CD temperature variations were fit to a two-state model that yielded lower T(m) values for Tyr containing mutants, indicating that Trp/Tyr and Tyr/Tyr interactions have less contribution to hairpin stability than the Trp/Trp interaction. Trp/Tyr interactions can provide significant stabilization, much greater than the Trp/aliphatic interaction, but Tyr/Tyr interactions are not as significant. Cross-strand interacting residues involving Trp with an edge-to-face orientation with Trp or Tyr had the strongest impact on hairpin stability.

  • Geometry and Efficacy of Trp-Trp, Trp-Tyr and Tyr-Tyr Aromatic Interaction in Cross-Strand Positions of a Designed β-Hairpin
    Biophysical Journal, 2010
    Co-Authors: Dan Mcelheny, Timothy A. Keiderling
    Abstract:

    Analysis of the impact of neighboring aromatic groups on structure can lead to improved understanding of protein folding mechanisms and stability. In this study, we examined the impact of varying aromatic interactions in cross-strand positions for Trpzip2, a β-hairpin forming peptide (Cochran et al., PNAS, 2001, 98, 5578-5583), by comparison of the interactions of Trp-Trp, Trp-Tyr and Tyr-Tyr. NMR and optical spectra (ECD, FTIR) of the original TZ2 peptide and its Tyr and Val-substituted mutants were analyzed to characterize their conformations and thermal stability. Cross-strand coupled Trp-Trp and Trp-Tyr pairs show unique, strong exciton bands in ECD while the Tyr-Tyr pair doesn't show any clear exciton band. The edge-to-face cross strand interaction leads to stable β-hairpin structures when Trps are at positions 2-11 or 4-9, but the alternate coupling for Trp at positions 2-9 does not lead to a stable structure. In Trpzip2 these would correspond to a more face-to-face interaction, which may contribute to the instability. When Tyr is substituted for Trp, the Trp-Trp interaction has more contribution to the peptide stabilization than does the Tyr-Tyr pair. When Tyr is substituted into position 4 and 11, the Trp-Tyr pair also has a unique geometry. These aromatic-aromatic interactions were also compared to simple hydrophobic interaction by contrasting stabilities of peptides with Val or Tyr substituted for two interacting Trp residues. Tyr is more stabilizing than Val for such substitutions which may indicate coupling of conjugated π-electron systems dominates stability. Aromatic interactions showed a stronger effect than hydrophobic interaction for stabilization. Extended kinetic studies using laser initiated T-jumps and IR detected conformational changes have helped sort out mechanistic aspects of this folding problem (Hauser et al, JACS, 2008, 130, 2984-2992).

M.a. Jimenez - One of the best experts on this subject based on the ideXlab platform.

  • ab type lectin toxin agglutinin from mistletoe differences in affinity of the two galactoside binding trp tyr sites and regulation of their functionality by monomer dimer equilibrium
    Glycobiology, 2006
    Co-Authors: M.a. Jimenez, Sabine André, Hans-c. Siebert, Hans-j. Gabius, Dolores Solís
    Abstract:

    Viscumin of mistletoe (Viscum album L.) has a concentrationdependent activity profile unique to plant AB-toxins. It starts with lectin-dependent mitogenicity and then covers toxicity and cell agglutination, associated with shifts in the monomer/ dimer equilibrium. Each lectin subunit harbors two sections for ligand contact. In the dimer, the B-chain sites in subdomain 2g (designated as the Tyr-sites) appear fully accessible, whereas Trp-sites in subdomain 1a are close to the dimer interface. It is unclear whether both types of sites operate similarly in binding glycoligands in solution. By systematically covering a broad range of lactose/lectin ratio in isothermal titration calorimetry, we obtained evidence for two sites showing dissimilar binding affinity. Intriguingly, the site with higher affinity was only partially occupied. To assign the observed properties to the Trp/ Tyr-sites, we next performed chemically induced dynamic nuclear polarization measurements of Trp and Tyr accessibility. A Tyr signal, but not distinct Trp peaks, was recorded when testing the dimer. Lactose-quenchable Trp peaks became visible on the destabilization of the dimer by citraconylation, intimating Trp involvement in ligand contact in the monomer. Fittingly, Tyr acetylation but not mild Trp oxidation reduced the dimer hemagglutination activity and the extent of binding to asialofetuin–Sepharose 4B. Altogether, the results attribute lectin activity in the dimer primarily to Tyr-sites. Full access to Trp-sites is gained on dimer dissociation. Thus, the monomer/ dimer equilibrium of viscumin regulates the operativity of these sites. Their structural divergence affords the possibility for differences in ligand selection when comparing monomers (Tyr- and Trp-sites) with dimers (primarily Tyr-sites).

  • AB-type lectin (toxin/agglutinin) from mistletoe: differences in affinity of the two galactoside-binding Trp/Tyr-sites and regulation of their functionality by monomer/dimer equilibrium
    Glycobiology, 2006
    Co-Authors: M.a. Jimenez, Sabine André, Hans-c. Siebert, Hans-j. Gabius, Dolores Solís
    Abstract:

    Viscumin of mistletoe (Viscum album L.) has a concentrationdependent activity profile unique to plant AB-toxins. It starts with lectin-dependent mitogenicity and then covers toxicity and cell agglutination, associated with shifts in the monomer/ dimer equilibrium. Each lectin subunit harbors two sections for ligand contact. In the dimer, the B-chain sites in subdomain 2g (designated as the Tyr-sites) appear fully accessible, whereas Trp-sites in subdomain 1a are close to the dimer interface. It is unclear whether both types of sites operate similarly in binding glycoligands in solution. By systematically covering a broad range of lactose/lectin ratio in isothermal titration calorimetry, we obtained evidence for two sites showing dissimilar binding affinity. Intriguingly, the site with higher affinity was only partially occupied. To assign the observed properties to the Trp/ Tyr-sites, we next performed chemically induced dynamic nuclear polarization measurements of Trp and Tyr accessibility. A Tyr signal, but not distinct Trp peaks, was recorded when testing the dimer. Lactose-quenchable Trp peaks became visible on the destabilization of the dimer by citraconylation, intimating Trp involvement in ligand contact in the monomer. Fittingly, Tyr acetylation but not mild Trp oxidation reduced the dimer hemagglutination activity and the extent of binding to asialofetuin–Sepharose 4B. Altogether, the results attribute lectin activity in the dimer primarily to Tyr-sites. Full access to Trp-sites is gained on dimer dissociation. Thus, the monomer/ dimer equilibrium of viscumin regulates the operativity of these sites. Their structural divergence affords the possibility for differences in ligand selection when comparing monomers (Tyr- and Trp-sites) with dimers (primarily Tyr-sites).

Dan Mcelheny - One of the best experts on this subject based on the ideXlab platform.

  • Geometry and Efficacy of Cross-Strand Trp/Trp, Trp/Tyr, and Tyr/Tyr Aromatic Interaction in a β-Hairpin Peptide
    Biochemistry, 2010
    Co-Authors: Dan Mcelheny, Takahiro Takekiyo, Timothy A. Keiderling
    Abstract:

    The Trpzip2 peptide (WTWENGKWTWK-NH(2)), designed by Cochran and co-workers, contains two pairs of Trp's having cross-strand interaction and forms a stable antiparallel beta-hairpin. In order to study the geometries and effects on the structure and stability of different aromatic interactions, selected tryptophan residues were substituted with Tyr to get three Trpzip2 mutants with different Trp/Trp, Trp/Tyr, and Tyr/Tyr interacting pairs. Their native-state structures were determined using two-dimensional (2D) NMR and shown to have the same cross-strand edge-to-face Trp/Trp interaction as that in Trpzip2 for the Trp/Trp pair. The analogous Trp/Tyr and Tyr/Tyr pairs also tended to have an edge-to-face geometry. The effects of specific Trp/Trp, Trp/Tyr, and Tyr/Tyr interactions on hairpin stability were studied by varying temperature and monitoring structure with electronic circular dichroism (CD) and infrared (IR) absorption spectra. IR and CD temperature variations were fit to a two-state model that yielded lower T(m) values for Tyr containing mutants, indicating that Trp/Tyr and Tyr/Tyr interactions have less contribution to hairpin stability than the Trp/Trp interaction. Trp/Tyr interactions can provide significant stabilization, much greater than the Trp/aliphatic interaction, but Tyr/Tyr interactions are not as significant. Cross-strand interacting residues involving Trp with an edge-to-face orientation with Trp or Tyr had the strongest impact on hairpin stability.

  • Geometry and Efficacy of Trp-Trp, Trp-Tyr and Tyr-Tyr Aromatic Interaction in Cross-Strand Positions of a Designed β-Hairpin
    Biophysical Journal, 2010
    Co-Authors: Dan Mcelheny, Timothy A. Keiderling
    Abstract:

    Analysis of the impact of neighboring aromatic groups on structure can lead to improved understanding of protein folding mechanisms and stability. In this study, we examined the impact of varying aromatic interactions in cross-strand positions for Trpzip2, a β-hairpin forming peptide (Cochran et al., PNAS, 2001, 98, 5578-5583), by comparison of the interactions of Trp-Trp, Trp-Tyr and Tyr-Tyr. NMR and optical spectra (ECD, FTIR) of the original TZ2 peptide and its Tyr and Val-substituted mutants were analyzed to characterize their conformations and thermal stability. Cross-strand coupled Trp-Trp and Trp-Tyr pairs show unique, strong exciton bands in ECD while the Tyr-Tyr pair doesn't show any clear exciton band. The edge-to-face cross strand interaction leads to stable β-hairpin structures when Trps are at positions 2-11 or 4-9, but the alternate coupling for Trp at positions 2-9 does not lead to a stable structure. In Trpzip2 these would correspond to a more face-to-face interaction, which may contribute to the instability. When Tyr is substituted for Trp, the Trp-Trp interaction has more contribution to the peptide stabilization than does the Tyr-Tyr pair. When Tyr is substituted into position 4 and 11, the Trp-Tyr pair also has a unique geometry. These aromatic-aromatic interactions were also compared to simple hydrophobic interaction by contrasting stabilities of peptides with Val or Tyr substituted for two interacting Trp residues. Tyr is more stabilizing than Val for such substitutions which may indicate coupling of conjugated π-electron systems dominates stability. Aromatic interactions showed a stronger effect than hydrophobic interaction for stabilization. Extended kinetic studies using laser initiated T-jumps and IR detected conformational changes have helped sort out mechanistic aspects of this folding problem (Hauser et al, JACS, 2008, 130, 2984-2992).

Hans-j. Gabius - One of the best experts on this subject based on the ideXlab platform.

  • ab type lectin toxin agglutinin from mistletoe differences in affinity of the two galactoside binding trp tyr sites and regulation of their functionality by monomer dimer equilibrium
    Glycobiology, 2006
    Co-Authors: M.a. Jimenez, Sabine André, Hans-c. Siebert, Hans-j. Gabius, Dolores Solís
    Abstract:

    Viscumin of mistletoe (Viscum album L.) has a concentrationdependent activity profile unique to plant AB-toxins. It starts with lectin-dependent mitogenicity and then covers toxicity and cell agglutination, associated with shifts in the monomer/ dimer equilibrium. Each lectin subunit harbors two sections for ligand contact. In the dimer, the B-chain sites in subdomain 2g (designated as the Tyr-sites) appear fully accessible, whereas Trp-sites in subdomain 1a are close to the dimer interface. It is unclear whether both types of sites operate similarly in binding glycoligands in solution. By systematically covering a broad range of lactose/lectin ratio in isothermal titration calorimetry, we obtained evidence for two sites showing dissimilar binding affinity. Intriguingly, the site with higher affinity was only partially occupied. To assign the observed properties to the Trp/ Tyr-sites, we next performed chemically induced dynamic nuclear polarization measurements of Trp and Tyr accessibility. A Tyr signal, but not distinct Trp peaks, was recorded when testing the dimer. Lactose-quenchable Trp peaks became visible on the destabilization of the dimer by citraconylation, intimating Trp involvement in ligand contact in the monomer. Fittingly, Tyr acetylation but not mild Trp oxidation reduced the dimer hemagglutination activity and the extent of binding to asialofetuin–Sepharose 4B. Altogether, the results attribute lectin activity in the dimer primarily to Tyr-sites. Full access to Trp-sites is gained on dimer dissociation. Thus, the monomer/ dimer equilibrium of viscumin regulates the operativity of these sites. Their structural divergence affords the possibility for differences in ligand selection when comparing monomers (Tyr- and Trp-sites) with dimers (primarily Tyr-sites).

  • AB-type lectin (toxin/agglutinin) from mistletoe: differences in affinity of the two galactoside-binding Trp/Tyr-sites and regulation of their functionality by monomer/dimer equilibrium
    Glycobiology, 2006
    Co-Authors: M.a. Jimenez, Sabine André, Hans-c. Siebert, Hans-j. Gabius, Dolores Solís
    Abstract:

    Viscumin of mistletoe (Viscum album L.) has a concentrationdependent activity profile unique to plant AB-toxins. It starts with lectin-dependent mitogenicity and then covers toxicity and cell agglutination, associated with shifts in the monomer/ dimer equilibrium. Each lectin subunit harbors two sections for ligand contact. In the dimer, the B-chain sites in subdomain 2g (designated as the Tyr-sites) appear fully accessible, whereas Trp-sites in subdomain 1a are close to the dimer interface. It is unclear whether both types of sites operate similarly in binding glycoligands in solution. By systematically covering a broad range of lactose/lectin ratio in isothermal titration calorimetry, we obtained evidence for two sites showing dissimilar binding affinity. Intriguingly, the site with higher affinity was only partially occupied. To assign the observed properties to the Trp/ Tyr-sites, we next performed chemically induced dynamic nuclear polarization measurements of Trp and Tyr accessibility. A Tyr signal, but not distinct Trp peaks, was recorded when testing the dimer. Lactose-quenchable Trp peaks became visible on the destabilization of the dimer by citraconylation, intimating Trp involvement in ligand contact in the monomer. Fittingly, Tyr acetylation but not mild Trp oxidation reduced the dimer hemagglutination activity and the extent of binding to asialofetuin–Sepharose 4B. Altogether, the results attribute lectin activity in the dimer primarily to Tyr-sites. Full access to Trp-sites is gained on dimer dissociation. Thus, the monomer/ dimer equilibrium of viscumin regulates the operativity of these sites. Their structural divergence affords the possibility for differences in ligand selection when comparing monomers (Tyr- and Trp-sites) with dimers (primarily Tyr-sites).