Harlen, O. G. | Search bioRxiv

bioRxiv2026

Stretching mucins: revealing the complex rheology of a natural gly coprotein network

Flow and extensional deformation of mucin networks are fundamental in mucus biophysics, governing how mucus functions as a protective and lubricating, and transport-facilitating layer. While the shear and oscillatory rheology of mucin solutions have been characterized in considerable detail, their behavior under extensional deformation remains comparatively understudied. Here, we report a concentration-dependent transition in extensional flow response of mucin solutions using a bespoke dripping-onto-substrate extensional rheometer. We show that mucin solutions at the lower concentrations undergo linear filament thinning, whereas semidilute mucin solutions form highly extensible filaments, with radius decaying exponentially in time, consistent with the elastocapillary thinning observed in solutions of high molecular weight synthetic polymers. Remarkably, at higher mucin concentrations inter-chain mucin associations produce a sudden reduction in the apparent elastocapillary relaxation time. We demonstrate how increasing macromolecular concentration redistributes the balance between viscous and elastic stresses during capillary thinning in a biopolymer network and reveal a concentration-driven reduction in mucin filament extensibility. O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=114 SRC="FIGDIR/small/725541v2_ufig1.gif" ALT="Figure 1"> View larger version (46K): org.highwire.dtl.DTLVardef@1f593acorg.highwire.dtl.DTLVardef@1b23686org.highwire.dtl.DTLVardef@119add3org.highwire.dtl.DTLVardef@e31908_HPS_FORMAT_FIGEXP M_FIG C_FIG

biophysics↗

bioRxiv2023

Exploiting cryo-EM structures of actomyosin-5a to reveal the physical properties of its lever

Myosin 5a (Myo5a) is a dimeric processive motor protein that transports cellular cargos along actin filaments. Its long lever is responsible for its large powerstroke, step size and load-bearing ability. Little is known about the levers structure and physical properties, and how they contribute to walking mechanics. Using cryo-electron microscopy and molecular dynamics simulations, we resolved the structure of monomeric Myo5a, comprising the motor domain and full-length lever, bound to F-actin. The range of its lever conformations revealed its physical properties, how stiffness varies along its length and predicts a large, 35 nm, working stroke. Thus, the newly released trail head in a dimeric Myo5a would only need to perform a small diffusive search for its new binding site on actin, and stress would only be generated across the dimer once phosphate is released from the lead head, revealing new insight into the walking behaviour of Myo5a.

biophysics↗