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Testing tube model predictions on semi-flexible polymer networks

Isoform- and PTM-specific, viscoelastic shear properties of actin

dc.contributor.advisorJanshoff, Andreas Prof. Dr.
dc.contributor.authorNietmann, Peter
dc.titleTesting tube model predictions on semi-flexible polymer networksde
dc.title.alternativeIsoform- and PTM-specific, viscoelastic shear properties of actinde
dc.contributor.refereeJanshoff, Andreas Prof. Dr.
dc.description.abstractengThe mechanical properties of simple entangled actin filament networks in eukaryotes are well understood as they are predictable with model systems. The high complexity of cellular actin structures like the cell cortex for example emerges from the dynamic interaction with a plethora of other proteins and ions, mainly actin binding proteins. This has been established knowledge for some time, but is it ultimately correct? The tube model for semi-flexible filaments is commonly applied to predict the network properties of microfilaments with single filament bending mechanics similar to those of F-actin. It is based purely on the filaments bending stiffness and geometric considerations. Following this logic, an exchange of F-actin with similarly sized filaments and similar bending properties should not affect the overall network response to deformation. But does this logic reflect the reality? This thesis investigated the raised questions by comparing the network shear response of DNA origami filament networks to those of F-actin networks. A clear difference could be shown. This is interesting on a theoretical level since the inter-filament interactions must be more complex than the assumed hard body interactions. Therefore, geometric considerations alone are not enough to predict network properties of semi-flexible filaments. But there are no such filaments present in the cytoplasm besides F-actin. The bending properties of other cellular filaments are vastly dissimilar from those of actin. However, there are different actin isoforms forming semi-flexible filaments in the cytoplasmic protein pool. They differ in a minuscule part of their amino acid sequence at the N-terminus, which is placed at the exterior of the filament. The comparison of entangled cytosolic gamma- and beta-actin networks revealed striking differences in the network stiffness. So even small variations in the amino acid sequence can have a significant effect on the bulk properties of the network. For instance, in some cases network mechanics are altered by orders of magnitude. Taking a closer look at the actin isoforms uncovers another layer of complexity hidden in the cellular machinery. In addition, these isoforms undergo post-translational modifications, which further differentiate actin filaments into a potential toolbox for the cell. To investigate electrostatic and steric causes of the observed phenomena, fluorecent labels were introduced and it was shown that a similar impact on the network stiffness could be achieved. The underlying causes of these different network mechanics of semi-flexible filaments are discussed and potential implications for in vitro as well as in vivo experiments are
dc.contributor.coRefereeKöster, Sarah Prof. Dr.
dc.contributor.thirdRefereeBetz, Timo Prof. Dr.
dc.contributor.thirdRefereeSollich, Peter Prof. Dr.
dc.contributor.thirdRefereeSalditt, Tim Prof. Dr.
dc.contributor.thirdRefereeSchäfer, Tim Dr.
dc.subject.engparticle trackingde
dc.subject.engDNA origamide
dc.subject.engBottom up approachde
dc.subject.engActin cortexde
dc.affiliation.instituteFakultät für Chemiede
dc.subject.gokfullChemie  (PPN62138352X)de
dc.notes.confirmationsentConfirmation sent 2023-11-13T19:45:01de

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