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Nature Communications 2021

Anillin generates tens of pico-Newton forces to slide actin filaments 
a Schematic representation of the experimental setup. b Time-lapse fluorescence micrographs showing an actin bundle attached between two silica microspheres. The bundle is being stretched as the left microsphere is pulled leftwards by an optical trap. c Typical force time-trace (top) and the force-distance curve (bottom) corresponding to stretching of an anillin-actin filament bundle (experimental data points—magenta). Asymptotic forces of individual stretching steps, calculated by fitting an exponential to the force decays (as shown in d), are indicated by black crosses. These increase hyperbolically with increasing distance between the microspheres, and thus with decreasing overlap length L. The green line represents ~1/L fit to the data. d Temporal response of the construct to stretching and relaxation; the left optical trap is moved 100 nm away from the right trap and then, after ~7 s, moved back to the original position. The temporal profile of the longitudinal position of the left optical trap is shown together with the detected distance between the microspheres (top) and the detected force (bottom). e The detected force increased with decreasing overlap length before the filaments slid apart completely (distance to disconnection = 0). All events longer than six steps are plotted (n = 11 experiments indicated by different colours). Inset, anillin density in the overlap (fluorescence intensity of anillin per unit length of the overlap) at the start and the end of the bundle stretching. Grey boxplots represent raw data, green boxplots represent data after photobleaching correction (see Fig. S2e for the photobleaching estimation) (n = 10 experiments). Corresponding data points overlay the boxplots. f, g Force response of a pre-stretched actin-anillin bundle to a decrease (f) or increase (g) of anillin-GFP concentration. Schematic representation of the experiment (top) and temporal experimental data (bottom). Decrease of the concentration (n = 15 events in 14 experiments), increase of the concentration (n = 15 events in 14 experiments). Green curves are the experimental data, mean temporal profile is shown in magenta. Box and whisker plots show a significant decrease or increase in force between time points 0 and 30 s after a decrease (one-sided Wilcoxon test, p = 0.02) or increase (one-sided Wilcoxon test, p = 0.03) of anillin-GFP concentration. In e–gdata were represented as boxplots. Central marks represent median, top and bottom edges of the box indicate the 75th and 25th percentiles, respectively. Whiskers extend the most extreme points that are not considered outliers. Outliers are marked as grey circles.

Zdeněk Lánský Research Group

 Significance

Constriction of the cytokinetic ring, a circular structure of actin filaments, is an essential step during cell division. Mechanical forces driving the constriction are attributed to myosin motor proteins, which slide actin filaments along each other. However, in multiple organisms, ring constriction has been reported to be myosin independent. How actin rings constrict in the absence of motor activity remains unclear. Here, we demonstrate that anillin, a non­motor actin crosslinker, indispensable during cytokinesis, autonomously propels the contractility of actin bundles. Anillin generates contractile forces of tens of pico-Newtons to maximise the lengths of overlaps between bundled actin filaments. The contractility is enhanced by actin disassembly. When multiple actin filaments are arranged into a ring, this contractility leads to ring constriction. Our results indicate that passive actin crosslinkers can substitute for the activity of molecular motors to generate contractile forces in a variety of actin networks, including the cytokinetic ring.

Nature Communications 2021

Nature Index Journal

EH domains of AtEH1/Pan1 differ in their Ca2+-binding capacities. a Domain organization of AtEH1/Pan1 and AtEH2/Pan1. Both proteins contain two Eps15 homology domains (EH), a coiled-coil domain (CC), and an acidic (A)-motif. A schematic representation of a multiple sequence alignment (MSA) - shows strong conservation of the EH domains (blue lines) across the plant kingdom. Percentages indicate the relative number of identical amino acids. b–g Cartoon representation of the X-ray structure of EH1.1 and NMR/all-atom molecular dynamics structure of EH1.2. Ions are shown as orange (Ca2+) or grey (Na+) spheres. Insets show the ion coordination in each EF-hand loop. Ca2+ coordinating residues and water molecules (W) are indicated in (c, d) and (f, g).

Savvas N. Savvides, Kostas Tripsianes, Roman Pleskot, and Daniel Van Damme Research Groups

Significance

Clathrin-mediated endocytosis (CME) is the gatekeeper of the plasma membrane. In contrast to animals and yeasts, CME in plants depends on the TPLATE complex (TPC), an evolutionary ancient adaptor complex. The mechanistic contribution of the individual TPC subunits to plant CME remains however elusive. In this study, we used a multidisciplinary approach to elucidate the structural and functional roles of the evolutionary conserved N-terminal Eps15 homology (EH) domains of the TPC subunit AtEH1/Pan1. By integrating high-resolution structural information obtained by X-ray crystallography and NMR spectroscopy with all-atom molecular dynamics simulations, we provide structural insight into the function of both EH domains. Both domains bind phosphatidic acid with a different strength, and only the second domain binds phosphatidylinositol 4,5-bisphosphate. Unbiased peptidome profiling by mass-spectrometry revealed that the first EH domain preferentially interacts with the double N-terminal NPF motif of a previously unidentified TPC interactor, the integral membrane protein Secretory Carrier Membrane Protein 5 (SCAMP5). Furthermore, we show that AtEH/Pan1 proteins control the internalization of SCAMP5 via this double NPF peptide interaction motif. Collectively, our structural and functional studies reveal distinct but complementary roles of the EH domains of AtEH/Pan1 in plant CME and connect the internalization of SCAMP5 to the TPLATE complex.

Yperman, K., Papageorgiou, A. C., Merceron, R., De Munck, S., Bloch, Y., Eeckhout,D., Jiang, Q., Tack, P., Grigoryan, R., Evangelidis, T., Van Leene, J., Vincze, L., , Vandenabeele, P., Vanhaecke, F., Potocký, M., De Jaeger, G., Savvides, S. N. , Tripsianes , K., Pleskot, R.  & Van Damme D.: Distinct EH domains of the endocytic TPLATE complex confer lipid and protein binding, Nature Comm. (2021) **, **  https://doi.org/10.1038/s41467-021-23314-6