Sevil Weinkauf - Academia.edu (original) (raw)

Papers by Sevil Weinkauf

The catalytic activity and selectivity of palladium supported on various metal oxides in carbon-c... more The catalytic activity and selectivity of palladium supported on various metal oxides in carbon-carbon coupling reactions of aryl bromides with styrene (Heck reaction) were investigated. The activity is determined by the nature of the oxide support and the Pd dispersion (structure-activity relationships). The relation of homogeneous (leaching) and heterogeneous mechanisms is discussed.

The Journal of Physical Chemistry B, 2007

Dense liquid phases, metastable with respect to a solid phase, but stable with respect to the sol... more Dense liquid phases, metastable with respect to a solid phase, but stable with respect to the solution, have been known to form in solutions of proteins and small-molecule substances. Here, with the protein lumazine synthase as a test system, using dynamic and static light scattering and atomic force microscopy, we demonstrate submicron size clusters of dense liquid. In contrast to the macroscopic dense liquid, these clusters are metastable not only with respect to the crystals, but also with respect to the low-concentration solution: the characteristic cluster lifetime is limited to ∼10 s, after which they decay. The cluster population is detectable only if they occupy >10 -6 of the solution volume and have a number density >10 5 cm -3 for 3 to 11% of the monitored time. The cluster volume fraction varies within wide limits and reaches up to 10 -3 . Increasing protein concentration increases the frequency of cluster detection but does not affect the ranges of the cluster sizes, suggesting that a preferred cluster size exists. A simple Monte Carlo model with protein-like potentials reproduces the metastable clusters of dense liquid with limited lifetimes and variable sizes and suggests that the mean cluster size is determined by the kinetics of growth and decay and not by thermodynamics.

Structure, 1995

Background: Tetrahydrobiopterin serves as the cofactor for enzymes involved in neurotransmitter b... more Background: Tetrahydrobiopterin serves as the cofactor for enzymes involved in neurotransmitter biosynthesis and as a regulatory factor in immune cell proliferation and the biosynthesis of melanin. The biosynthetic pathway to tetrahydrobiopterin consists of three steps starting from GTP. The initial reaction is catalyzed by GTP cyclohydrolase I (GTP-CH-I) and involves the chemically complex transformation of the purine into the pterin ring system.Results The crystal structure of the Escherichia coli GTP-CH-I was solved by single isomorphous replacement and molecular averaging at 3.0 å resolution. The functional enzyme is a homodecameric complex with D5 symmetry, forming a torus with dimensions 65 å × 100 å. The pentameric subunits are constructed via an unprecedented cyclic arrangement of the four-stranded antiparallel β-sheets of the five monomers to form a 20-stranded antiparallel β-barrel of 35 å diameter. Two pentamers are tightly associated by intercalation of two antiparallel ...

Physical Chemistry Chemical Physics, 2005

Fuel cell electrocatalysts usually feature high noble metal contents, and these favour particle a... more Fuel cell electrocatalysts usually feature high noble metal contents, and these favour particle agglomeration. In this paper a variety of synthetic approaches (wet chemical deposition, electrodeposition and electrodeposition on chemically preformed Pt nuclei) is employed to shed light on the ...

Molecular and Cellular Biology, 2014

Mutations in the leucine-rich repeat kinase 2 gene (LRRK2) are associated with familial and spora... more Mutations in the leucine-rich repeat kinase 2 gene (LRRK2) are associated with familial and sporadic Parkinson's disease (PD). LRRK2 is a complex protein that consists of multiple domains, including predicted C-terminal WD40 repeats. In this study, we analyzed functional and molecular features conferred by the WD40 domain. Electron microscopic analysis of the purified LRRK2 C-terminal domain revealed doughnut-shaped particles, providing experimental evidence for its WD40 fold. We demonstrate that LRRK2 WD40 binds and sequesters synaptic vesicles via interaction with vesicle-associated proteins. In fact, a domain-based pulldown approach combined with mass spectrometric analysis identified LRRK2 as being part of a highly specific protein network involved in synaptic vesicle trafficking. In addition, we found that a C-terminal sequence variant associated with an increased risk of developing PD, G2385R, correlates with a reduced binding affinity of LRRK2 WD40 to synaptic vesicles. Our data demonstrate a critical role of the WD40 domain within LRRK2 function.

Journal of The Royal Society Interface, 2010

Migration of the Pachycondyla marginata ant is significantly oriented at 138 with respect to the ... more Migration of the Pachycondyla marginata ant is significantly oriented at 138 with respect to the geomagnetic north-south axis. On the basis of previous magnetic measurements of individual parts of the body (antennae, head, thorax and abdomen), the antennae were suggested to host a magnetoreceptor. In order to identify Fe 3þ /Fe 2þ sites in antennae tissue, we used light microscopy on Prussian/Turnbull's blue-stained tissue. Further analysis using transmission electron microscopy imaging and diffraction, combined with elemental analysis, revealed the presence of ultra-fine-grained crystals (20-100 nm) of magnetite/maghaemite (Fe 3 O 4 /g-Fe 2 O 3 ), haematite (a-Fe 2 O 3 ), goethite (a-FeOOH) besides (alumo)silicates and Fe/Ti/O compounds in different parts of the antennae, that is, in the joints between the third segment/pedicel, pedicel/scape and scape/head, respectively. The presence of (alumo)silicates and Fe/Ti/O compounds suggests that most, if not all, of the minerals in the tissue are incorporated soil particles rather than biomineralized by the ants. However, as the particles were observed within the tissue, they do not represent contamination. The amount of magnetic material associated with Johnston's organ and other joints appears to be sufficient to produce a magnetic-field-modulated mechanosensory output, which may therefore underlie the magnetic sense of the migratory ant.

Journal of the American Chemical Society, 2005

Dense liquid phases, metastable with respect to a solid phase, form in solutions of proteins and ... more Dense liquid phases, metastable with respect to a solid phase, form in solutions of proteins and small-molecule materials. They have been shown to serve as a prerequisite for the nucleation of crystals and other ordered solid phases. Here, using crystals of the protein lumazine synthase from Bacillus subtilis, which grow by the generation and spreading of layers, we demonstrate that within a range of supersaturations the only mechanism of generation of growth layers involves the association of submicrometer-size droplets of the dense liquid to the crystal surface. The dense liquid is metastable not only with respect to the crystals, but also with respect to the low-concentration solution: dynamic light scattering reveals that the droplets' lifetime is limited to several seconds, after which they decay into the low-concentration solution. The short lifetime does not allow growth to detectable dimensions so that liquidliquid phase separation is not observed within a range of conditions broader than the one used for crystallization. If during their lifetime the droplets encounter a crystal surface, they lower their free energy not by decay, but by transformation into crystalline matter, ensuring perfect registry with the substrate. These observations illustrate two novel features of phase transformations in solutions: the existence of doubly metastable, short-lifetime dense phases and their crucial role for the growth of an ordered solid phase.

Journal of Molecular Biology, 1995

A monoclinic crystal modification of GTP cyclohydrolase I (space group P2 1 , 1 Department of Che... more A monoclinic crystal modification of GTP cyclohydrolase I (space group P2 1 , 1 Department of Chemistry a = 204.2 Å, b = 210.4 Å, c = 71.8 Å, a = g = 90°, b = 95.8°) was studied by Technical University of freeze-etching electron microscopy and by Patterson correlation techniques.

Journal of Crystal Growth, 2005

We use atomic force microscopy to explore the mechanisms of crystal growth of the protein lumazin... more We use atomic force microscopy to explore the mechanisms of crystal growth of the protein lumazine synthase. We find that at moderate supersaturations, the only mechanism of layer generation on the (001) face is via landing of ∼100nm large dense objects. After landing on the crystal surface, the objects flatten and yield stacks of steps. These steps merge continuously with each other and with the underlying lattice. These observations allow us to conclude that the dense objects are not microcrystals nucleated in the solution, but are droplets of the dense liquid phase. Dynamic light scattering revealed the presence of dense liquid droplets, which are metastable with respect to the solution, have a finite lifetime of several seconds, radii of 50–200nm, and consist of 102–104 molecules. Under the influence of the periodic field of the crystal upon landing on the crystal surface, these droplets stabilize and transform into stacks of crystalline layers, whose spreading results in crystal growth. Since crystals of this protein do not have dislocations, and two-dimensional (2D) nucleation of new layers does not occur, likely because of high barriers, the sedimentation and structuring of metastable droplets of protein-rich liquid is the only mechanism providing for crystal growth.

ChemPhysChem, 2006

Cell-penetrating peptides (CPPs) are short polycationic sequences that can translocate into cells... more Cell-penetrating peptides (CPPs) are short polycationic sequences that can translocate into cells without disintegrating the plasma membrane. CPPs are useful tools for delivering cargo, but their molecular mechanism of crossing the lipid bilayer remains unclear. Here we study the interaction of the HIV-derived CPP TAT (48-60) with model membranes by solid-state NMR spectroscopy and electron microscopy. The peptide induces a pronounced isotropic (31)P NMR signal in zwitterionic DMPC, but not in anionic DMPG bilayers. Octaarginine and to a lesser extent octalysine have the same effect, in contrast to other cationic amphiphilic membrane-active peptides. The observed non-lamellar lipid morphology is attributed to specific interactions of polycationic peptides with phosphocholine head groups, rather than to electrostatic interactions. Freeze-fracture electron microscopy indicates that TAT(48-60) induces the formation of rodlike, presumably inverted micelles in DMPC, which may represent intermediates during the translocation across eukaryotic membranes.

Chemistry - A European Journal, 1996

The synthesis and properties of [Ga(N,),], (1) and the related derivatives [(Do),Ga(N,),] (2a-d: ... more The synthesis and properties of [Ga(N,),], (1) and the related derivatives [(Do),Ga(N,),] (2a-d: Do = THF, NEt,, NMe,, quinuclidine, n = 1; 2e: Do = pyridine; n = 3)

Molecular Cell, 2010

Hsp12 of S. cerevisiae is upregulated several 100-fold in response to stress. Our phenotypic anal... more Hsp12 of S. cerevisiae is upregulated several 100-fold in response to stress. Our phenotypic analysis showed that this protein is important for survival of a variety of stress conditions, including high temperature. In the absence of Hsp12, we observed changes in cell morphology under stress conditions. Surprisingly, in the cell, Hsp12 exists both as a soluble cytosolic protein and associated to the plasma membrane. The in vitro analysis revealed that Hsp12, unlike all other Hsps studied so far, is completely unfolded; however, in the presence of certain lipids, it adopts a helical structure. The presence of Hsp12 does not alter the overall lipid composition of the plasma membrane but increases membrane stability.

The catalytic activity and selectivity of palladium supported on various metal oxides in carbon-c... more The catalytic activity and selectivity of palladium supported on various metal oxides in carbon-carbon coupling reactions of aryl bromides with styrene (Heck reaction) were investigated. The activity is determined by the nature of the oxide support and the Pd dispersion (structure-activity relationships). The relation of homogeneous (leaching) and heterogeneous mechanisms is discussed.

The Journal of Physical Chemistry B, 2007

Dense liquid phases, metastable with respect to a solid phase, but stable with respect to the sol... more Dense liquid phases, metastable with respect to a solid phase, but stable with respect to the solution, have been known to form in solutions of proteins and small-molecule substances. Here, with the protein lumazine synthase as a test system, using dynamic and static light scattering and atomic force microscopy, we demonstrate submicron size clusters of dense liquid. In contrast to the macroscopic dense liquid, these clusters are metastable not only with respect to the crystals, but also with respect to the low-concentration solution: the characteristic cluster lifetime is limited to ∼10 s, after which they decay. The cluster population is detectable only if they occupy >10 -6 of the solution volume and have a number density >10 5 cm -3 for 3 to 11% of the monitored time. The cluster volume fraction varies within wide limits and reaches up to 10 -3 . Increasing protein concentration increases the frequency of cluster detection but does not affect the ranges of the cluster sizes, suggesting that a preferred cluster size exists. A simple Monte Carlo model with protein-like potentials reproduces the metastable clusters of dense liquid with limited lifetimes and variable sizes and suggests that the mean cluster size is determined by the kinetics of growth and decay and not by thermodynamics.

Structure, 1995

Background: Tetrahydrobiopterin serves as the cofactor for enzymes involved in neurotransmitter b... more Background: Tetrahydrobiopterin serves as the cofactor for enzymes involved in neurotransmitter biosynthesis and as a regulatory factor in immune cell proliferation and the biosynthesis of melanin. The biosynthetic pathway to tetrahydrobiopterin consists of three steps starting from GTP. The initial reaction is catalyzed by GTP cyclohydrolase I (GTP-CH-I) and involves the chemically complex transformation of the purine into the pterin ring system.Results The crystal structure of the Escherichia coli GTP-CH-I was solved by single isomorphous replacement and molecular averaging at 3.0 å resolution. The functional enzyme is a homodecameric complex with D5 symmetry, forming a torus with dimensions 65 å × 100 å. The pentameric subunits are constructed via an unprecedented cyclic arrangement of the four-stranded antiparallel β-sheets of the five monomers to form a 20-stranded antiparallel β-barrel of 35 å diameter. Two pentamers are tightly associated by intercalation of two antiparallel ...

Physical Chemistry Chemical Physics, 2005

Fuel cell electrocatalysts usually feature high noble metal contents, and these favour particle a... more Fuel cell electrocatalysts usually feature high noble metal contents, and these favour particle agglomeration. In this paper a variety of synthetic approaches (wet chemical deposition, electrodeposition and electrodeposition on chemically preformed Pt nuclei) is employed to shed light on the ...

Molecular and Cellular Biology, 2014

Mutations in the leucine-rich repeat kinase 2 gene (LRRK2) are associated with familial and spora... more Mutations in the leucine-rich repeat kinase 2 gene (LRRK2) are associated with familial and sporadic Parkinson's disease (PD). LRRK2 is a complex protein that consists of multiple domains, including predicted C-terminal WD40 repeats. In this study, we analyzed functional and molecular features conferred by the WD40 domain. Electron microscopic analysis of the purified LRRK2 C-terminal domain revealed doughnut-shaped particles, providing experimental evidence for its WD40 fold. We demonstrate that LRRK2 WD40 binds and sequesters synaptic vesicles via interaction with vesicle-associated proteins. In fact, a domain-based pulldown approach combined with mass spectrometric analysis identified LRRK2 as being part of a highly specific protein network involved in synaptic vesicle trafficking. In addition, we found that a C-terminal sequence variant associated with an increased risk of developing PD, G2385R, correlates with a reduced binding affinity of LRRK2 WD40 to synaptic vesicles. Our data demonstrate a critical role of the WD40 domain within LRRK2 function.

Journal of The Royal Society Interface, 2010

Migration of the Pachycondyla marginata ant is significantly oriented at 138 with respect to the ... more Migration of the Pachycondyla marginata ant is significantly oriented at 138 with respect to the geomagnetic north-south axis. On the basis of previous magnetic measurements of individual parts of the body (antennae, head, thorax and abdomen), the antennae were suggested to host a magnetoreceptor. In order to identify Fe 3þ /Fe 2þ sites in antennae tissue, we used light microscopy on Prussian/Turnbull's blue-stained tissue. Further analysis using transmission electron microscopy imaging and diffraction, combined with elemental analysis, revealed the presence of ultra-fine-grained crystals (20-100 nm) of magnetite/maghaemite (Fe 3 O 4 /g-Fe 2 O 3 ), haematite (a-Fe 2 O 3 ), goethite (a-FeOOH) besides (alumo)silicates and Fe/Ti/O compounds in different parts of the antennae, that is, in the joints between the third segment/pedicel, pedicel/scape and scape/head, respectively. The presence of (alumo)silicates and Fe/Ti/O compounds suggests that most, if not all, of the minerals in the tissue are incorporated soil particles rather than biomineralized by the ants. However, as the particles were observed within the tissue, they do not represent contamination. The amount of magnetic material associated with Johnston's organ and other joints appears to be sufficient to produce a magnetic-field-modulated mechanosensory output, which may therefore underlie the magnetic sense of the migratory ant.

Journal of the American Chemical Society, 2005

Dense liquid phases, metastable with respect to a solid phase, form in solutions of proteins and ... more Dense liquid phases, metastable with respect to a solid phase, form in solutions of proteins and small-molecule materials. They have been shown to serve as a prerequisite for the nucleation of crystals and other ordered solid phases. Here, using crystals of the protein lumazine synthase from Bacillus subtilis, which grow by the generation and spreading of layers, we demonstrate that within a range of supersaturations the only mechanism of generation of growth layers involves the association of submicrometer-size droplets of the dense liquid to the crystal surface. The dense liquid is metastable not only with respect to the crystals, but also with respect to the low-concentration solution: dynamic light scattering reveals that the droplets' lifetime is limited to several seconds, after which they decay into the low-concentration solution. The short lifetime does not allow growth to detectable dimensions so that liquidliquid phase separation is not observed within a range of conditions broader than the one used for crystallization. If during their lifetime the droplets encounter a crystal surface, they lower their free energy not by decay, but by transformation into crystalline matter, ensuring perfect registry with the substrate. These observations illustrate two novel features of phase transformations in solutions: the existence of doubly metastable, short-lifetime dense phases and their crucial role for the growth of an ordered solid phase.

Journal of Molecular Biology, 1995

A monoclinic crystal modification of GTP cyclohydrolase I (space group P2 1 , 1 Department of Che... more A monoclinic crystal modification of GTP cyclohydrolase I (space group P2 1 , 1 Department of Chemistry a = 204.2 Å, b = 210.4 Å, c = 71.8 Å, a = g = 90°, b = 95.8°) was studied by Technical University of freeze-etching electron microscopy and by Patterson correlation techniques.

Journal of Crystal Growth, 2005

We use atomic force microscopy to explore the mechanisms of crystal growth of the protein lumazin... more We use atomic force microscopy to explore the mechanisms of crystal growth of the protein lumazine synthase. We find that at moderate supersaturations, the only mechanism of layer generation on the (001) face is via landing of ∼100nm large dense objects. After landing on the crystal surface, the objects flatten and yield stacks of steps. These steps merge continuously with each other and with the underlying lattice. These observations allow us to conclude that the dense objects are not microcrystals nucleated in the solution, but are droplets of the dense liquid phase. Dynamic light scattering revealed the presence of dense liquid droplets, which are metastable with respect to the solution, have a finite lifetime of several seconds, radii of 50–200nm, and consist of 102–104 molecules. Under the influence of the periodic field of the crystal upon landing on the crystal surface, these droplets stabilize and transform into stacks of crystalline layers, whose spreading results in crystal growth. Since crystals of this protein do not have dislocations, and two-dimensional (2D) nucleation of new layers does not occur, likely because of high barriers, the sedimentation and structuring of metastable droplets of protein-rich liquid is the only mechanism providing for crystal growth.

ChemPhysChem, 2006

Cell-penetrating peptides (CPPs) are short polycationic sequences that can translocate into cells... more Cell-penetrating peptides (CPPs) are short polycationic sequences that can translocate into cells without disintegrating the plasma membrane. CPPs are useful tools for delivering cargo, but their molecular mechanism of crossing the lipid bilayer remains unclear. Here we study the interaction of the HIV-derived CPP TAT (48-60) with model membranes by solid-state NMR spectroscopy and electron microscopy. The peptide induces a pronounced isotropic (31)P NMR signal in zwitterionic DMPC, but not in anionic DMPG bilayers. Octaarginine and to a lesser extent octalysine have the same effect, in contrast to other cationic amphiphilic membrane-active peptides. The observed non-lamellar lipid morphology is attributed to specific interactions of polycationic peptides with phosphocholine head groups, rather than to electrostatic interactions. Freeze-fracture electron microscopy indicates that TAT(48-60) induces the formation of rodlike, presumably inverted micelles in DMPC, which may represent intermediates during the translocation across eukaryotic membranes.

Chemistry - A European Journal, 1996

The synthesis and properties of [Ga(N,),], (1) and the related derivatives [(Do),Ga(N,),] (2a-d: ... more The synthesis and properties of [Ga(N,),], (1) and the related derivatives [(Do),Ga(N,),] (2a-d: Do = THF, NEt,, NMe,, quinuclidine, n = 1; 2e: Do = pyridine; n = 3)

Molecular Cell, 2010

Hsp12 of S. cerevisiae is upregulated several 100-fold in response to stress. Our phenotypic anal... more Hsp12 of S. cerevisiae is upregulated several 100-fold in response to stress. Our phenotypic analysis showed that this protein is important for survival of a variety of stress conditions, including high temperature. In the absence of Hsp12, we observed changes in cell morphology under stress conditions. Surprisingly, in the cell, Hsp12 exists both as a soluble cytosolic protein and associated to the plasma membrane. The in vitro analysis revealed that Hsp12, unlike all other Hsps studied so far, is completely unfolded; however, in the presence of certain lipids, it adopts a helical structure. The presence of Hsp12 does not alter the overall lipid composition of the plasma membrane but increases membrane stability.