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91 Publications visible to you, out of a total of 91
The role of flow in the self-assembly of dragline spider silk proteins

Abstract (Expand)

Hydrodynamic flow in the spider duct induces conformational changes in dragline spider silk proteins (spidroins) and drives their assembly, but the underlying physical mechanisms are still elusive. … Here we address this challenging multiscale problem with a complementary strategy of atomistic and coarse-grained molecular dynamics simulations with uniform flow. The conformational changes at the molecular level were analyzed for single-tethered spider silk peptides. Uniform flow leads to coiled-to-stretch transitions and pushes alanine residues into β sheet and poly-proline II conformations. Coarse-grained simulations of the assembly process of multiple semi-flexible block copolymers using multi-particle collision dynamics reveal that the spidroins aggregate faster but into low-order assemblies when they are less extended. At medium-to-large peptide extensions (50%–80%), assembly slows down and becomes reversible with frequent association and dissociation events, whereas spidroin alignment increases and alanine repeats form ordered regions. Our work highlights the role of flow in guiding silk self-assembly into tough fibers by enhancing alignment and kinetic reversibility, a mechanism likely relevant also for other proteins whose function depends on hydrodynamic flow.

Authors: Ana M. Herrera-Rodríguez, Anil Kumar Dasanna, Csaba Daday, Eduardo R. Cruz-Chú, Camilo Aponte-Santamaría, Ulrich S. Schwarz, Frauke Gräter

Date Published: 5th Oct 2023

Publication Type: Journal

Allosteric activation of vinculin by talin

Abstract (Expand)

The talin-vinculin axis is a key mechanosensing component of cellular focal adhesions. How talin and vinculin respond to forces and regulate one another remains unclear. By combining single molecule … magnetic tweezer experiments, Molecular Dynamics simulations, actin bundling assays, and adhesion assembly experiments in live cells, we here discover a two-ways allosteric network within vinculin as a regulator of the talin-vinculin interaction. We directly observe a maturation process of vinculin upon talin binding which reinforces the binding to talin at a rate of 0.03 s−1. This allosteric transition can compete with force-induced dissociation of vinculin from talin only at 7-10 pN. Mimicking the allosteric activation by mutation yields a vinculin molecule that bundles actin and localizes to focal adhesions in a force-independent manner. Hence, the allosteric switch confines talin-vinculin interactions and focal adhesion build-up to intermediate force levels. The ‘allosteric vinculin mutant’ is a valuable molecular tool to further dissect the mechanical and biochemical signalling circuits at focal adhesions and elsewhere.

Authors: Florian Franz, Rafael Tapia-Rojo, Sabina Winograd-Katz, Rajaa Boujemaa-Paterski, Wenhong Li, Tamar Unger, Shira Albeck, Camilo Aponte-Santamaría, Sergi Garcia-Manyes, Ohad Medalia, Benjamin Geiger, Frauke Gräter

Date Published: 18th Jul 2023

Publication Type: Journal

Collagen breaks at weak sacrificial bonds taming its mechanoradicals

Abstract (Expand)

Collagen is a force-bearing, hierarchical structural protein important to all connective tissue. In tendon collagen, high load even below macroscopic failure level creates mechanoradicals by homolytic … bond scission, similar to polymers. The location and type of initial rupture sites critically decide on both the mechanical and chemical impact of these micro-ruptures on the tissue, but are yet to be explored. We here use scale-bridging simulations supported by gel electrophoresis and mass spectrometry to determine breakage points in collagen. We find collagen crosslinks, as opposed to the backbone, to harbor the weakest bonds, with one particular bond in trivalent crosslinks as the most dominant rupture site. We identify this bond as sacrificial, rupturing prior to other bonds while maintaining the material’s integrity. Also, collagen’s weak bonds funnel ruptures such that the potentially harmful mechanoradicals are readily stabilized. Our results suggest this unique failure mode of collagen to be tailored towards combatting an early onset of macroscopic failure and material ageing.

Authors: Benedikt Rennekamp, Christoph Karfusehr, Markus Kurth, Aysecan Ünal, Kai Riedmiller, Ganna Gryn’ova, David M. Hudson, Frauke Gräter

Date Published: 12th Apr 2023

Publication Type: Journal

Disulfide Bond Reduction and Exchange in von-Willebrand-Factor’s C4-Domain Undermines Platelet Binding

Abstract

Not specified

Authors: Fabian Kutzki, Diego Butera, Angelina J. Lay, Denis Maag, Joyce Chiu, Heng-Giap Woon, Tomáš Kubař, Marcus Elstner, Camilo Aponte-Santamaría, Philip J. Hogg, Frauke Gräter

Date Published: 12th Apr 2023

Publication Type: Journal

Mechano-Redox Control of Macrophage-1 Antigen De-Adhesion From ICAM-1 (Intercellular Adhesion Molecule 1) by Protein Disulfide Isomerase Promotes Directional Movement Under Flow

Abstract (Expand)

BACKGROUND: Neutrophil migration is critical to the initiation and resolution of inflammation. Macrophage-1 antigen (Mac-1; CD11b/CD18, αMβ2) is a leukocyte integrin essential for firm adhesion to …firm adhesion to endothelial ICAM-1 (intercellular adhesion molecule 1) and migration of neutrophils in the shear forces of the circulation. PDI (protein disulfide isomerase) has been reported to influence neutrophil adhesion and migration. We aimed to elucidate the molecular mechanism of PDI control of Mac-1 affinity for ICAM-1 during neutrophil migration under fluid shear. METHODS: Neutrophils isolated from whole blood were perfused over microfluidic chips coated with ICAM-1. Colocalization of Mac-1 and PDI on neutrophils was visualized by fluorescently labeled antibodies and confocal microscopy. The redox state of Mac-1 disulfide bonds was mapped by differential cysteine alkylation and mass spectrometry. Wild-type or disulfide mutant Mac-1 was expressed recombinantly in Baby Hamster Kidney cells to measure ligand affinity. Mac-1 conformations were measured by conformation-specific antibodies and molecular dynamics simulations. Neutrophils crawling on immobilized ICAM-1 were measured in presence of oxidized or reduced PDI, and the effect of PDI inhibition using isoquercetin on neutrophil crawling on inflamed endothelial cells was examined. Migration indices in the X- and Y-direction were determined and the crawling speed was calculated. RESULTS: PDI colocalized with high-affinity Mac-1 at the trailing edge of stimulated neutrophils when crawling on ICAM-1 under fluid shear. PDI cleaved 2 allosteric disulfide bonds, C169-C176 and C224-C264, in the βI domain of the β2 subunit, and cleavage of the C224-C264 disulfide bond selectively controls Mac-1 disengagement from ICAM-1 under fluid shear. Molecular dynamics simulations and conformation-specific antibodies reveal that cleavage of the C224-C264 bond induces conformational change and mechanical stress in the βI domain. This allosterically alters the exposure of an αI domain epitope associated with a shift of Mac-1 to a lower-affinity state. These molecular events promote neutrophil motility in the direction of flow at high shear stress. Inhibition of PDI by isoquercetin reduces neutrophil migration in the direction of flow on endothelial cells during inflammation. CONCLUSIONS: Shear-dependent PDI cleavage of the neutrophil Mac-1 C224-C264 disulfide bond triggers Mac-1 de-adherence from ICAM-1 at the trailing edge of the cell and enables directional movement of neutrophils during inflammation.

Authors: Alexander Dupuy, Camilo Aponte Santamaría, Adva Yeheskel, Elinor Hortle, Stefan H. Oehlers, Frauke Gräter, Philip J. Hogg, Freda H. Passam, Joyce Chiu

Date Published: 6th Apr 2023

Publication Type: Journal

DOPA Residues Endow Collagen with Radical Scavenging Capacity

Abstract (Expand)

Here we uncover collagen, the main structural protein of all connective tissues, as a redox-active material. We identify dihydroxyphenylalanine (DOPA) residues, post-translational oxidation products … of tyrosine residues, to be common in collagen derived from different connective tissues. We observe that these DOPA residues endow collagen with substantial radical scavenging capacity. When reducing radicals, DOPA residues work as redox relay: they convert to the quinone and generate hydrogen peroxide. In this dual function, DOPA outcompetes its amino acid precursors and ascorbic acid. Our results establish DOPA residues as redox-active side chains of collagens, probably protecting connective tissues against radicals formed under mechanical stress and/or inflammation.

Authors: Markus Kurth, Uladzimir Barayeu, Hassan Gharibi, Andrei Kuzhelev, Kai Riedmiller, Jennifer Zilke, Kasimir Noack, Vasyl Denysenkov, Reinhard Kappl, Thomas F. Prisner, Roman A. Zubarev, Tobias P. Dick, Frauke Gräter

Date Published: 3rd Apr 2023

Publication Type: Journal

Energetics and kinetics of membrane permeation of photoresists for bioprinting

Abstract

Not specified

Authors: Lucas Diedrich, Matthias Brosz, Tobias Abele, Salome Steinke, Frauke Gräter, Kerstin Göpfrich, Camilo Aponte-Santamaría

Date Published: 28th Mar 2023

Publication Type: Journal

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