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Stefan Matile

Publications and source records attributed to Stefan Matile.

46 records · Page 3Linked to original sources
PubMed2003

Synthetic multifunctional pores: deletion and inversion of anion/cation selectivity using pM and pH.

We report the characterization of multifunctional rigid-rod beta-barrel ion channels with either internal aspartates or arginine-histidine dyads by planar bilayer conductance experiments. Barrels with internal aspartates form cation selective, large, unstable and ohmic barrel-stave (rather than toroidal) pores; addition of magnesium cations nearly deletes cation selectivity and increases single-channel stability. Barrels with internal arginine-histidine dyads form cation selective (PK/Pc1 = 2.1), small and ohmic ion channels with superb stability (single-channel lifetime > 20 seconds). Addition of "protons" results in inversion of anion/cation selectivity (Pc1-/Pk+ = 3.8); addition of an anionic guest (HPTS) results in the blockage of anion selective but not cation selective channels. These results suggest that specific, internal counterion immobilization, here magnesium (but not sodium or potassium) cations by internal aspartates and inorganic phosphates by internal arginines (but not histidines), provides access to synthetic multifunctional pores with attractive properties.

Journal Article↗
PubMed2003

Complementary characteristics of homologous p-octiphenyl beta-barrels with ion channel and esterase activity.

We report that decreasing beta-sheet length in homologous multifunctional rigid-rod beta-barrels with internal histidines increases ion channel stability by three orders of magnitude, reduces binding activity by four orders of magnitude, and reduces esterase activity up to 22-times. These results are further used to evaluate methods employed to characterize suprastructure and activity of synthetic multifunctional pores formed by p-octiphenyl beta-barrels with emphasis on applicability of the Hille model to determine internal diameters and the Woodhull equation to locate internal active sites.

Algorithms↗
PubMed2003

Voltage-dependent formation of anion channels by synthetic rigid-rod push-pull beta-barrels.

Ion channels formed by p-octiphenyls equipped with amphiphilic, cationic tripeptide strands and either with (5) or without (6) axial dipole moment are described (preliminary communication: N. Sakai, S. Matile, J. Am. Chem. Soc. 2002, 124, 1184-1185). Fluorescence kinetics with variably polarized neutral or anionic vesicles, together with planar bilayer conductance measurements, reveal voltage dependence with weakly lyotropic anion selectivity, and deactivation by competing surface potentials of the ion channels formed by asymmetric 5. In planar bilayers, 5 forms short-lived, poorly organized channels--similar to those produced by alpha-helical natural antibiotics--capable of transforming into stable, ohmic p-octiphenyl "beta-barrel" ion channels similar to those of the >99 % homologous but symmetric 6. Fluorescence depth quenching and circular dichroism studies confirm the effect of membrane potentials in promotion of the partitioning of 5 (but not 6) into the bilayers, identifying partitioning as the voltage-dependent step.

Anions↗
PubMed2003

G-quartet self-assembly under osmotic pressure: remote control by vesicle shrinking rather than stress.

Does osmotic pressure stimulate assembly or disassembly of supramolecules in vesicles? Self-assembly was conceivable as intravesicular response to osmotic shrinking upon application of extravesicular overpressure, whereas disassembly was conceivable as a response to bilayer stress in hyperosmotic vesicles. Self-assembly of guanosine 5'-monophosphates (GMPs) into G-quartets was selected to investigate the nature of remote control of supramolecular chemistry within vesicles by osmotic pressure. Using circular dichroism spectroscopy to selectively detect G-quartets, we found that extravesicular overpressure stimulates intravesicular self-assembly, whereas underpressure stimulates disassembly. G-quartet self-assembly by osmotic pressure exhibited ion-selective metal-cation templation, as expected. The key conclusions are that supramolecular chemistry within vesicles is governed by vesicle shape rather than vesicle stress and that detection of osmotic pressure by CD spectroscopy is an interesting alternative to the commonly used methods based on fluorescence self-quenching.

Circular Dichroism↗
PubMed2002

Fluorometric detection of enzyme activity with synthetic supramolecular pores.

The reversible blockage of synthetic pores formed by rigid-rod beta barrels, either by substrates or products, was used to sense a variety of enzymatic reactions in high-throughput format with "naked-eye" fluorescent detection. Improvement of sensor sensitivity beyond three orders of magnitude by straightforward internal mutations underscores the functional plasticity of rigid-rod beta barrels. Such detectors of enzyme activity with the aforementioned characteristics are needed in areas as diverse as proteomics and environmentally benign organic synthesis.

Adenosine Triphosphate↗
PubMed2002

Binding of organic anions by synthetic supramolecular metallopores with internal Mg2+-aspartate complexes.

We report that cation-selective transmembrane pores formed by synthetic p-octiphenyl beta barrels with internal aspartate residues can be transformed into anion-permeable metallopores with internal Mg(2+)-aspartate complexes. These metallopores are shown to be useful for fluorimetric sensing of a broad variety of organic anions of biological relevance such as phytate, heparin, thiamine phosphates, and adenosine triphosphate. The negligible flippase activity measurable for Mg(2+)-free pores indicates that transmembrane p-octiphenyl beta barrels do not disturb the lipid bilayer suprastructure, in other words, they form barrel-stave rather than toroidal pores.

Anions↗
PubMed2002

Transmembrane pores formed by synthetic p-octiphenyl beta-barrels with internal carboxylate clusters: regulation of ion transport by pH and Mg(2+)- complexed 8-aminonaphthalene-1,3,6-trisulfonate.

Design, synthesis, and study of a synthetic barrel-stave supramolecule with p-octiphenyl "staves," beta-sheet "hoops," and hydrophobic exterior as well as internal carboxylate clusters are reported. Ion transport experiments indicate the formation of transmembrane pores at 5 < pH < 7 with nanomolar activity. Blockage of dye efflux from spherical bilayers by external Mg(OAc)(2) and internal 8-aminonaphthalene-1,3,6-trisulfonate is suggestive for weakly cooperative (n = 1.16) formation of aspartate-Mg(2+)-8-aminonaphthalene-1,3,6-trisulfonate complexes within the barrel-stave supramolecule (K(D) = 2.9 mM). Corroborative evidence from structural studies by circular dichroism spectroscopy is provided and discussed with emphasis of the importance of internal charge repulsion for pore formation and future applications toward binding and catalysis within supramolecular synthetic pores.

Biological Transport↗
PubMed2002

Recognition of polarized lipid bilayers by p-oligophenyl ion channels: from push-pull rods to push-pull barrels.

Design, synthesis, and evaluation of 14-methoxy-84-methylsulfonyl-22,33,42,53,62,73-hexa(Gla-Leu-Lys-Leu-NH2)-p-octiphenyl (1) and 14,84-bismethoxy-22,33,42,53,62,73-hexa(Gla-Leu-Lys-Leu-NH2)-p-octiphenyl (2) are described (Gla = -OCH2CO-). Nanomolar concentrations of push-pull rod 1 are found to suffice to selectively form ion channels in polarized spherical bilayer membranes composed of egg yolk phosphatidylcholine. Exponential dependence of the ion-channel activity on membrane polarization reveals a gating charge of 0.85/channel. Independence of the activity of push-push rod 2 on membrane potential demonstrates that cell membrane recognition originates from the axial dipole in push-pull rod 1. Nonlinear concentration dependence of activity at -180 mV indicates parallel self-assembly of push-pull rod 1 into a tetrameric barrel-stave supramolecule.

Ion Channels↗
PubMed2002

Toward catalytic rigid-rod beta-barrels: a hexamer with multiple histidines.

Rigid-rod beta-barrels are composed of interdigitating, short, amphiphilic peptide strands that are flanked by stabilizing rigid-rod "staves." As a first step toward the construction of catalytic rigid-rod beta-barrels, we here report synthesis and study of a new barrel designed to comprise alternating leucine and histidine residues at the inner and lysine and glutamate residues at the outer barrel surface. Synthesis of p-octiphenyls with lateral tripeptide strands followed procedures described previously. Barrel formation by programmed assembly of complementary tripeptide-p-octiphenyl rods was monitored by circular dichroism (CD). CD-mixing curves (Job-plots) were consistent with 1:1-stoichiometry. Guanidinium chloride denaturation experiments gave a DeltaG(H20) = -1.8 kcal mol(-1) with a C(50) = 1.9 M. Size exclusion chromatography suggested quantitative formation of a hexamer. Facile barrel deconstruction by acid and divalent cations demonstrated the presence of internal, nonproximal histidines. Inclusion complex formation with fluorescent guests corroborated internal hydrophobicity of beta-barrel hosts and potential for intratoroidal catalysis.

Journal Article↗