Biology subjects

Adriaans, I. E.

Publications and source records attributed to Adriaans, I. E..

3 recordsLinked to original sources

bioRxiv2026

Intrafilament nucleotide exchange in a prokaryotic actin homolog

Polymerization and disassembly govern the cellular functions of cytoskeletal proteins. Canonical nucleotide-dependent polymers, including actin and microtubules, renew their nucleotide state through subunit subunit dissociation, nucleotide exchange in solution and repolymerization. Yet the assembly dynamics of the membrane-bound bacterial actin MreB remain unresolved. Here, using total internal reflection fluorescence microscopy and high-speed atomic force microscopy, we visualise Bacillus subtilis MreB assembly on supported lipid bilayers in real time. ATP binding drives polymerization into symmetrically elongating filaments, whereas ATP hydrolysis within filaments promotes disassembly. Unexpectedly, nucleotides continuously exchange within membrane-bound filaments without detectable subunit turnover, coupling filament stability to the surrounding nucleotide pool: ATP exchange stabilizes filaments, whereas ADP exchange triggers rapid fragmentation and disassembly. Monte-Carlo modelling and single-cell in vivo imaging support this mechanism. Thus, intrafilament nucleotide exchange enables MreB filaments to renew their nucleotide state without polymer turnover, revealing nucleotide-state rejuvenation as a new mode of biological polymer regulation.

microbiology↗

bioRxiv2025

Architecture and function of Bud3 and Bud4-induced septin structures

At the time of cytokinesis, a double septin ring is assembled at the division site in many eukaryotic cells. In budding yeast the double ring is made by two arrays of circumferential septin filaments at the two sides of the bud neck, which are thought to compartmentalize the membrane around the cleavage site. Integrity of the double septin ring requires the anillin Bud4 and its presumed partner Bud3, which associate with septins in mitosis and have separate, yet unknown, roles in stabilizing septin circumferential filaments. Through in vitro reconstitution assays using purified proteins, we show that Bud3 and Bud4 organise septin filaments in distinct ways, while together they cooperate to assemble higher-order septin networks. In agreement with their separate roles in septin organization, Bud3 and Bud4 bind to different septins and require septins to associate with each other, indicating that they modulate septin architecture independently but synergistically. We also provide evidence that Bud3 and Bud4 bind membranes in vivo and in vitro, consistent with the presence of lipid-binding domains in their primary sequence. Using bud3 bud4 double mutants that lack the septin double ring, we show that in vivo proteins marking cytokinetic remnants require the double ring to efficiently concentrate at the division site, while other proteins landing at the bud neck at cytokinesis are unaffected. Thus, we propose that a septin double ring may imprint a selective spatial memory for cytokinesis that is transmitted throughout subsequent cell divisions.

cell biology↗

bioRxiv2018

PLK1 plays dual roles in centralspindlin regulation during cytokinesis

Cytokinesis starts in anaphase with the formation of an actomyosin-based contractile ring at the equatorial cortex, which is governed by the local activation of the small GTPase RhoA. Here we delineated the contributions of PLK1 and Aurora B to RhoA activation and cytokinesis initiation in human cells. Knock-down of PRC1, which disrupts the spindle midzone, revealed the existence of two pathways that can initiate cleavage furrow ingression. One pathway depends on a well-organized spindle midzone and PLK1, while the other depends on Aurora B activity and centralspindlin oligomerization at the equatorial cortex and can operate independently of PLK1. We further show that PLK1 inhibition sequesters centralspindlin onto the spindle midzone making it unavailable for Aurora B-dependent oligomerization at the equatorial cortex. We propose that PLK1 activity promotes the release of centralspindlin from the spindle midzone through inhibition of PRC1, allowing centralspindlin to function as a regulator of spindle midzone formation and as an activator of RhoA at the equatorial cortex.

cell biology↗