scholarly journals Type V myosin focuses the polarisome and shapes the tip of yeast cells

2021 ◽  
Vol 220 (5) ◽  
Author(s):  
Alexander Dünkler ◽  
Marcin Leda ◽  
Jan-Michael Kromer ◽  
Joachim Neller ◽  
Thomas Gronemeyer ◽  
...  
Keyword(s):  
Point Mutation ◽  
Filamentous Fungi ◽  
Actin Filaments ◽  
Binding Domain ◽  
Yeast Cells ◽  
Secretory Vesicles ◽  
Biophysical Modeling ◽  
Molecular Forces ◽  
Type V ◽  
Compact Shape

The polarisome is a cortical proteinaceous microcompartment that organizes the growth of actin filaments and the fusion of secretory vesicles in yeasts and filamentous fungi. Polarisomes are compact, spotlike structures at the growing tips of their respective cells. The molecular forces that control the form and size of this microcompartment are not known. Here we identify a complex between the polarisome subunit Pea2 and the type V Myosin Myo2 that anchors Myo2 at the cortex of yeast cells. We discovered a point mutation in the cargo-binding domain of Myo2 that impairs the interaction with Pea2 and consequently the formation and focused localization of the polarisome. Cells carrying this mutation grow round instead of elongated buds. Further experiments and biophysical modeling suggest that the interactions between polarisome-bound Myo2 motors and dynamic actin filaments spatially focus the polarisome and sustain its compact shape.

scholarly journals Type V Myosin focuses the polarisome and shapes the tip of yeast cells

2020 ◽  
Author(s):  
Alexander Dünkler ◽  
Marcin Leda ◽  
Jan-Michael Kromer ◽  
Joachim Neller ◽  
Thomas Gronemeyer ◽  
...  
Keyword(s):  
Point Mutation ◽  
Filamentous Fungi ◽  
Actin Filaments ◽  
Yeast Cells ◽  
Secretory Vesicles ◽  
Biophysical Modeling ◽  
Multiple Copies ◽  
Molecular Forces ◽  
Type V ◽  
Compact Shape

AbstractThe polarisome is a cortical proteinaceous micro-compartment that organizes the growth of actin filaments and the fusion of secretory vesicles in yeasts and filamentous fungi. Polarisomes are compact, spot-like structures at the growing tips of their respective cells. The molecular forces that control form and size of this micro-compartment are not known. Here we identify a complex between the polarisome subunit Pea2 and the type V Myosin Myo2 that anchors Myo2 at the cortex of yeast cells. We discovered a point mutation in the cargo-binding domain of Myo2 that impairs the interaction with Pea2 and consequently the formation and focused localization of the polarisome. Cells carrying this mutation grow round instead of elongated buds. Further experiments and biophysical modeling suggest that polarisome nanoparticles use multiple copies of Myo2 and an actin filament polymerizing activity to drive the assembly of the polarisome and sustain its compact shape.

scholarly journals A formin-nucleated actin aster concentrates cell wall hydrolases for cell fusion in fission yeast

2015 ◽  
Vol 208 (7) ◽  
pp. 897-911 ◽  
Author(s):  
Omaya Dudin ◽  
Felipe O. Bendezú ◽  
Raphael Groux ◽  
Thierry Laroche ◽  
Arne Seitz ◽  
...  
Keyword(s):  
Cell Wall ◽  
Fission Yeast ◽  
Cell Fusion ◽  
Actin Filaments ◽  
Yeast Cells ◽  
Structured Illumination ◽  
Structured Illumination Microscopy ◽  
M Cell ◽  
Cell Wall Hydrolases ◽  
Type V

Cell–cell fusion is essential for fertilization. For fusion of walled cells, the cell wall must be degraded at a precise location but maintained in surrounding regions to protect against lysis. In fission yeast cells, the formin Fus1, which nucleates linear actin filaments, is essential for this process. In this paper, we show that this formin organizes a specific actin structure—the actin fusion focus. Structured illumination microscopy and live-cell imaging of Fus1, actin, and type V myosins revealed an aster of actin filaments whose barbed ends are focalized near the plasma membrane. Focalization requires Fus1 and type V myosins and happens asynchronously always in the M cell first. Type V myosins are essential for fusion and concentrate cell wall hydrolases, but not cell wall synthases, at the fusion focus. Thus, the fusion focus focalizes cell wall dissolution within a broader cell wall synthesis zone to shift from cell growth to cell fusion.

scholarly journals Spindle orientation in Saccharomyces cerevisiae depends on the transport of microtubule ends along polarized actin cables

2003 ◽  
Vol 161 (3) ◽  
pp. 483-488 ◽  
Author(s):  
Eric Hwang ◽  
Justine Kusch ◽  
Yves Barral ◽  
Tim C. Huffaker
Keyword(s):  
Saccharomyces Cerevisiae ◽  
Actin Filaments ◽  
Yeast Cells ◽  
Similar Process ◽  
Spindle Orientation ◽  
Yeast Saccharomyces Cerevisiae ◽  
Cytoplasmic Microtubules ◽  
Actin Cables ◽  
Type V

Microtubules and actin filaments interact and cooperate in many processes in eukaryotic cells, but the functional implications of such interactions are not well understood. In the yeast Saccharomyces cerevisiae, both cytoplasmic microtubules and actin filaments are needed for spindle orientation. In addition, this process requires the type V myosin protein Myo2, the microtubule end–binding protein Bim1, and Kar9. Here, we show that fusing Bim1 to the tail of the Myo2 is sufficient to orient spindles in the absence of Kar9, suggesting that the role of Kar9 is to link Myo2 to Bim1. In addition, we show that Myo2 localizes to the plus ends of cytoplasmic microtubules, and that the rate of movement of these cytoplasmic microtubules to the bud neck depends on the intrinsic velocity of Myo2 along actin filaments. These results support a model for spindle orientation in which a Myo2–Kar9–Bim1 complex transports microtubule ends along polarized actin cables. We also present data suggesting that a similar process plays a role in orienting cytoplasmic microtubules in mating yeast cells.

scholarly journals αE-catenin actin-binding domain alters actin filament conformation and regulates binding of nucleation and disassembly factors

2013 ◽  
Vol 24 (23) ◽  
pp. 3710-3720 ◽  
Author(s):  
Scott D. Hansen ◽  
Adam V. Kwiatkowski ◽  
Chung-Yueh Ouyang ◽  
HongJun Liu ◽  
Sabine Pokutta ◽  
...  
Keyword(s):  
Actin Filament ◽  
Actin Filaments ◽  
Binding Domain ◽  
Actin Binding ◽  
Filamentous Actin ◽  
Filament Structure ◽  
Actin Binding Domain ◽  
Filament Bundles ◽  
Underlying Mechanisms ◽  
Cell Cell

The actin-binding protein αE-catenin may contribute to transitions between cell migration and cell–cell adhesion that depend on remodeling the actin cytoskeleton, but the underlying mechanisms are unknown. We show that the αE-catenin actin-binding domain (ABD) binds cooperatively to individual actin filaments and that binding is accompanied by a conformational change in the actin protomer that affects filament structure. αE-catenin ABD binding limits barbed-end growth, especially in actin filament bundles. αE-catenin ABD inhibits actin filament branching by the Arp2/3 complex and severing by cofilin, both of which contact regions of the actin protomer that are structurally altered by αE-catenin ABD binding. In epithelial cells, there is little correlation between the distribution of αE-catenin and the Arp2/3 complex at developing cell–cell contacts. Our results indicate that αE-catenin binding to filamentous actin favors assembly of unbranched filament bundles that are protected from severing over more dynamic, branched filament arrays.

scholarly journals The actin side-binding domain of gelsolin also caps actin filaments. Implications for actin filament severing

1994 ◽  
Vol 269 (13) ◽  
pp. 9473-9479
Author(s):  
H.Q. Sun ◽  
D.C. Wooten ◽  
P.A. Janmey ◽  
H.L. Yin
Keyword(s):  
Actin Filament ◽  
Actin Filaments ◽  
Binding Domain

scholarly journals The Cooh-Terminal Domain of Myo2p, a Yeast Myosin V, Has a Direct Role in Secretory Vesicle Targeting

1999 ◽  
Vol 147 (4) ◽  
pp. 791-808 ◽  
Author(s):  
Daniel Schott ◽  
Jackson Ho ◽  
David Pruyne ◽  
Anthony Bretscher
Keyword(s):  
Secretory Vesicle ◽  
Restrictive Temperature ◽  
Secretory Vesicles ◽  
Tail Domain ◽  
Myosin V ◽  
Direct Role ◽  
Rab Protein ◽  
Polarized Delivery ◽  
Actin Cables ◽  
Type V

MYO2 encodes a type V myosin heavy chain needed for the targeting of vacuoles and secretory vesicles to the growing bud of yeast. Here we describe new myo2 alleles containing conditional lethal mutations in the COOH-terminal tail domain. Within 5 min of shifting to the restrictive temperature, the polarized distribution of secretory vesicles is abolished without affecting the distribution of actin or the mutant Myo2p, showing that the tail has a direct role in vesicle targeting. We also show that the actin cable–dependent translocation of Myo2p to growth sites does not require secretory vesicle cargo. Although a fusion protein containing the Myo2p tail also concentrates at growth sites, this accumulation depends on the polarized delivery of secretory vesicles, implying that the Myo2p tail binds to secretory vesicles. Most of the new mutations alter a region of the Myo2p tail conserved with vertebrate myosin Vs but divergent from Myo4p, the myosin V involved in mRNA transport, and genetic data suggest that the tail interacts with Smy1p, a kinesin homologue, and Sec4p, a vesicle-associated Rab protein. The data support a model in which the Myo2p tail tethers secretory vesicles, and the motor transports them down polarized actin cables to the site of exocytosis.

scholarly journals Two New Ypt GTPases Are Required for Exit From the Yeast trans-Golgi Compartment

1997 ◽  
Vol 137 (3) ◽  
pp. 563-580 ◽  
Author(s):  
Gregory Jedd ◽  
Jon Mulholland ◽  
Nava Segev
Keyword(s):  
Protein Transport ◽  
Small Gtpases ◽  
Yeast Cells ◽  
Secretory Vesicles ◽  
Golgi Compartment ◽  
Rab Family ◽  
Vacuolar Protein ◽  
Exocytic Pathway ◽  
Mutant Cells

Small GTPases of the Ypt/rab family are involved in the regulation of vesicular transport. These GTPases apparently function during the targeting of vesicles to the acceptor compartment. Two members of the Ypt/rab family, Ypt1p and Sec4p, have been shown to regulate early and late steps of the yeast exocytic pathway, respectively. Here we tested the role of two newly identified GTPases, Ypt31p and Ypt32p. These two proteins share 81% identity and 90% similarity, and belong to the same protein subfamily as Ypt1p and Sec4p. Yeast cells can tolerate deletion of either the YPT31 or the YPT32 gene, but not both. These observations suggest that Ypt31p and Ypt32p perform identical or overlapping functions. Cells deleted for the YPT31 gene and carrying a conditional ypt32 mutation exhibit protein transport defects in the late exocytic pathway, but not in vacuolar protein sorting. The ypt31/ 32 mutant secretory defect is clearly downstream from that displayed by a ypt1 mutant and is similar to that of sec4 mutant cells. However, electron microscopy revealed that while sec4 mutant cells accumulate secretory vesicles, ypt31/32 mutant cells accumulate aberrant Golgi structures. The ypt31/32 phenotype is epistatic to that of a sec1 mutant, which accumulates secretory vesicles. Together, these results indicate that the Ypt31/32p GTPases are required for a step that occurs in the transGolgi compartment, between the reactions regulated by Ypt1p and Sec4p. This step might involve budding of vesicles from the trans-Golgi. Alternatively, Ypt31/ 32p might promote secretion indirectly, by allowing fusion of recycling vesicles with the trans-Golgi compartment.

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