About

Kurt Amann is not explicitly described in the provided page text, which primarily focuses on Sarah Ives, a biomedical researcher and UW–Madison alumnus. The text details her educational background, career, and public recognition, but does not include specific information about Kurt Amann's research focus, background, or key contributions.

Research topics

• Biology
• Cell biology
• Biophysics
• Chemistry
• Biochemistry

Selected publications

• A22 Disrupts the Bacterial Actin Cytoskeleton by Directly Binding and Inducing a Low-Affinity State in MreB

  Biochemistry · 2009-04-21 · 174 citations

  articleOpen accessSenior author

  S-(3,4-Dichlorobenzyl)isothiourea (A22) disrupts the actin cytoskeleton of bacteria, causing defects of morphology and chromosome segregation. Previous studies have suggested that the actin homologue MreB itself is the target of A22, but there has been no direct observation of A22 binding to MreB and no mechanistic explanation of its mode of action. We show that A22 binds MreB with at least micromolar affinity in its nucleotide-binding pocket in a manner that is sterically incompatible with simultaneous ATP binding. A22 negatively affects both the time course and extent of MreB polymerization in vitro in the presence of ATP. A22 prevents assembly of MreB into long, rigid polymers, as determined by both fluorescence microscopy and sedimentation assays. A22 increases the critical concentration of ATP-bound MreB assembly from 500 nM to approximately 2000 nM. We therefore conclude that A22 is a competitive inhibitor of ATP binding to MreB. A22-bound MreB is capable of polymerization, but with assembly properties that more closely resemble those of the ADP-bound state. Because the cellular concentration of MreB is in the low micromolar range, this mechanism explains the ability of A22 to largely disassemble the actin cytoskeleton in bacterial cells. It also represents a novel mode of action for a cytoskeletal drug and the first biochemical characterization of the interaction between a small molecule inhibitor of the bacterial cytoskeleton and its target.

  PublisherOA PDFDOI

• The structural basis of actin filament branching by the Arp2/3 complex

  The Journal of Cell Biology · 2008-03-03 · 304 citations

  articleOpen access

  The actin-related protein 2/3 (Arp2/3) complex mediates the formation of branched actin filaments at the leading edge of motile cells and in the comet tails moving certain intracellular pathogens. Crystal structures of the Arp2/3 complex are available, but the architecture of the junction formed by the Arp2/3 complex at the base of the branch was not known. In this study, we use electron tomography to reconstruct the branch junction with sufficient resolution to show how the Arp2/3 complex interacts with the mother filament. Our analysis reveals conformational changes in both the mother filament and Arp2/3 complex upon branch formation. The Arp2 and Arp3 subunits reorganize into a dimer, providing a short-pitch template for elongation of the daughter filament. Two subunits of the mother filament undergo conformational changes that increase stability of the branch. These data provide a rationale for why branch formation requires cooperative interactions among the Arp2/3 complex, nucleation-promoting factors, an actin monomer, and the mother filament.

  PublisherOA PDFDOI

• Assembly properties of the <i>Bacillus subtilis</i> actin, MreB

  Cell Motility and the Cytoskeleton · 2008-12-30 · 41 citations

  articleSenior authorCorresponding

  The bacterial actin MreB has been implicated in a variety of cellular roles including cell shape determination, cell wall synthesis, chromosome condensation and segregation, and the establishment and maintenance of cell polarity. Toward elucidating a clearer understanding of how MreB functions inside the bacterial cell, we investigated biochemically the polymerization of MreB from Bacillus subtilis. Light scattering and sedimentation assays revealed pH-, ionic-, cationic-, and temperature-dependent behavior. B. subtilis MreB polymerizes in the presence of millimolar divalent cations in a protein concentration-dependent manner. Polymerization is favored by decreasing pH and inhibited by monovalent salts and low temperatures. Although B. subtilis MreB binds and hydrolyzes both ATP and GTP, it does not require a bound nucleotide for assembly and polymerizes indistinguishably regardless of the nucleotide species bound, with a critical concentration of approximately 900 nM. A number of the presently reported properties of B. subtilis MreB differ significantly from those of T. maritima MreB1 (Bean and Amann [2008]: Biochemistry 47: 826-835), including the nucleotide requirements and temperature and ionic effects on polymerization state. These observations collectively suggest that additional factors interact with MreB to account for its complex dynamic behavior in cells.

  PublisherDOI

• Polymerization Properties of the<i>Thermotoga maritima</i>Actin MreB:  Roles of Temperature, Nucleotides, and Ions

  Biochemistry · 2007-12-21 · 57 citations

  articleOpen accessSenior author

  MreB is a bacterial orthologue of actin that affects cell shape, polarity, and chromosome segregation. Although a significant body of work has explored its cellular functions, we know very little about the biochemical behavior of MreB. We have cloned, overexpressed in Escherichia coli, and purified untagged MreB1 from Thermotoga maritima. We have characterized the conditions that regulate its monomer-to-polymer assembly reaction, the critical concentrations of that reaction, the manner in which MreB uses nucleotides, its stability, and the structure of the assembled polymer. MreB requires a bound purine nucleotide for polymerization and rapidly hydrolyzes it following assembly. MreB assembly contains two distinct components, one that does not require divalent cations and one that does, which may comprise the nucleation and elongation phases of assembly, respectively. MreB assembly is strongly favored by increasing temperature or protein concentration but inhibited differentially by high concentrations of monovalent salts. The polymerization rate increases and the bulk critical concentration decreases with increasing temperature, but in contrast to previous reports, MreB is capable of polymerizing across a broad range of temperatures. MreB polymers are shorter and stiffer and scatter more light than eukaryotic actin filaments. Due to rapid ATP hydrolysis and phosphate release, we suggest that most assembled MreB in cells is in the ADP-bound state. Because of only moderate differences between the ATP and ADP critical concentrations, treadmilling may occur, but we do not predict dynamic instability in cells. Because of the relatively low cellular concentration of MreB and the observed structural properties of the polymer, a single MreB assembly may exist in cells.

  PublisherOA PDFDOI

• Proteolysis of Cortactin by Calpain Regulates Membrane Protrusion during Cell Migration

  Molecular Biology of the Cell · 2005-11-10 · 116 citations

  articleOpen access

  Calpain 2 regulates membrane protrusion during cell migration. However, relevant substrates that mediate the effects of calpain on protrusion have not been identified. One potential candidate substrate is the actin binding protein cortactin. Cortactin is a Src substrate that drives actin polymerization by activating the Arp2/3 complex and also stabilizes the cortical actin network. We now provide evidence that proteolysis of cortactin by calpain 2 regulates membrane protrusion dynamics during cell migration. We show that cortactin is a calpain 2 substrate in fibroblasts and that the preferred cleavage site occurs in a region between the actin binding repeats and the alpha-helical domain. We have generated a mutant cortactin that is resistant to calpain proteolysis but retains other biochemical properties of cortactin. Expression of the calpain-resistant cortactin, but not wild-type cortactin, impairs cell migration and increases transient membrane protrusion, suggesting that calpain proteolysis of cortactin limits membrane protrusions and regulates migration in fibroblasts. Furthermore, the enhanced protrusion observed with the calpain-resistant cortactin requires both the Arp2/3 binding site and the Src homology 3 domain of cortactin. Together, these findings suggest a novel role for calpain-mediated proteolysis of cortactin in regulating membrane protrusion dynamics during cell migration.

  PublisherOA PDFDOI

• EPLIN regulates actin dynamics by cross-linking and stabilizing filaments

  The Journal of Cell Biology · 2003-02-03 · 181 citations

  articleOpen access

  Epithelial protein lost in neoplasm (EPLIN) is a cytoskeleton-associated protein encoded by a gene that is down-regulated in transformed cells. EPLIN increases the number and size of actin stress fibers and inhibits membrane ruffling induced by Rac. EPLIN has at least two actin binding sites. Purified recombinant EPLIN inhibits actin filament depolymerization and cross-links filaments in bundles. EPLIN does not affect the kinetics of spontaneous actin polymerization or elongation at the barbed end, but inhibits branching nucleation of actin filaments by Arp2/3 complex. Side binding activity may stabilize filaments and account for the inhibition of nucleation mediated by Arp2/3 complex. We propose that EPLIN promotes the formation of stable actin filament structures such as stress fibers at the expense of more dynamic actin filament structures such as membrane ruffles. Reduced expression of EPLIN may contribute to the motility of invasive tumor cells.

  PublisherOA PDFDOI

• The Arp2/3 complex nucleates actin filament branches from the sides of pre-existing filaments

  Nature Cell Biology · 2001-02-16 · 236 citations

  article1st authorCorresponding
  PublisherDOI

• Direct real-time observation of actin filament branching mediated by Arp2/3 complex using total internal reflection fluorescence microscopy

  Proceedings of the National Academy of Sciences · 2001-12-11 · 267 citations

  articleOpen access1st author

  Existing methods for studying actin filament dynamics have allowed analysis only of bulk samples or individual filaments after treatment with the drug phalloidin, which perturbs filament dynamics. Total internal reflection fluorescence microscopy with rhodamine-labeled actin allowed us to observe polymerization in real time, without phalloidin. Direct measurements of filament growth confirmed the rate constants measured by electron microscopy and established that rhodamine actin is a kinetically inactive tracer for imaging. In the presence of activated Arp2/3 complex, growing actin filaments form branches at random sites along their sides, rather than preferentially from their barbed ends.

  PublisherOA PDFDOI

• Structure of Arp2/3 Complex in Its Activated State and in Actin Filament Branch Junctions

  Science · 2001-09-28 · 250 citations

  article

  The seven-subunit Arp2/3 complex choreographs the formation of branched actin networks at the leading edge of migrating cells. When activated by Wiskott-Aldrich Syndrome protein (WASp), the Arp2/3 complex initiates actin filament branches from the sides of existing filaments. Electron cryomicroscopy and three-dimensional reconstruction of Acanthamoeba castellanii and Saccharomyces cerevisiae Arp2/3 complexes bound to the WASp carboxy-terminal domain reveal asymmetric, oblate ellipsoids. Image analysis of actin branches indicates that the complex binds the side of the mother filament, and Arp2 and Arp3 (for actin-related protein) are the first two subunits of the daughter filament. Comparison to the actin-free, WASp-activated complexes suggests that branch initiation involves large-scale structural rearrangements within Arp2/3.

  PublisherDOI

• Cellular regulation of actin network assembly

  Current Biology · 2000-10-01 · 33 citations

  articleOpen access1st authorCorresponding
  PublisherOA PDFDOI

Recent grants

• NIH Grant F32GM020638

  NIH · $64k

• Molecular Interactions of the Bacterial Actin, MreB

  NSF · $510k · 2008–2014

Frequent coauthors

• Thomas D. Pollard

  Yale University

  10 shared

• James Ervasti

  University of Minnesota

  6 shared

• Niels Volkmann

  4 shared

• Inna N. Rybakova

  University of Wisconsin–Madison

  4 shared

• Dorit Hanein

  4 shared

• Rong Li

  Qingdao University of Science and Technology

  3 shared

• Brian A. Renley

  Abbott Fund

  3 shared

• John E. Heuser

  Washington University in St. Louis

  3 shared

Labs

• Molecular and Cell Biology LeadershipPI

Awards & honors

• honored for research in animal embryo development