Myosin-X: a molecular motor at the cell's fingertips

doi:10.1016/j.tcb.2005.08.006

Trends in Cell Biology

Volume 15, Issue 10, October 2005, Pages 533-539

https://doi.org/10.1016/j.tcb.2005.08.006 Get rights and content

Research in several areas, including unconventional myosins and deafness genes, has converged recently on a group of myosins whose tails contain myosin tail homology 4 (MyTH4) and band 4.1, ezrin, radixin, moesin (FERM) domains. Although these ‘MyTH-FERM’ myosins are not present in yeast and plants, they are present in slime molds, worms, flies and mammals, where they mediate interactions between the cytoskeleton and the plasma membrane. The most broadly distributed MyTH-FERM myosin in vertebrate cells appears to be myosin-X (Myo10). This myosin can act as a link to integrins and microtubules, stimulate the formation of filopodia and undergo a novel form of motility within filopodia.

Introduction

The actin-based motor proteins of the myosin superfamily power many cellular movements. The myosin superfamily can be divided into at least 20 structurally and functionally distinct classes [1]. However, it is sometimes operationally split into the ‘conventional myosins’, which are responsible for processes such as muscle contraction, and the ‘unconventional myosins’, a category that contains all other myosins. Virtually all myosins have a general body plan consisting of a conserved myosin-head domain, which functions as a motor, a neck domain, which binds to light chains of the calmodulin superfamily and often acts as a switch to regulate motor activity, and a specialized tail domain that is responsible for processes such as cargo binding. Although myosins have long been hypothesized to be involved in phagocytosis and the extension of cellular processes, classic deletion experiments in the slime mold Dictyostelium reveal that these processes occur in the absence of conventional myosin (class II) [2], thus focusing attention on the unconventional myosins. One large group of unconventional myosins (classes VII, X, XII and XV) has been recognized recently as sharing a conserved structural feature in their tail domains–the presence of a myosin tail homology 4 (MyTH4) domain followed by a band 4.1, ezrin, radixin, moesin (FERM) domain. This has led to the suggestion that these myosins constitute a ‘superclass’ of structurally related myosins (Figure 1) 1, 3. The initial characterization of MyTH-FERM myosins such as myosin-X (Myo10) indicates that they might be key mediators of membrane–cytoskeleton interactions in processes such as phagocytosis and the extension of filopodia.

Section snippets

Discovery and structure of Myo10

Myo10 was discovered originally in a PCR screen to identify myosins that are expressed in the inner ear [4]. Phylogenetic analysis of the motor domain of Myo10 revealed that it was not closely related to known myosins and is the founding member of a novel class of myosins called the class X myosins. The full-length Myo10 heavy chain is ∼240 kDa and can be divided into a head, neck and tail (Figure 2) 5, 6. As with other myosins, the head functions as a motor domain and can bind to actin

Distribution and biochemical properties of Myo10

Myo10 appears to be vertebrate specific and is not present in either C. elegans or Drosophila. Although Myo10 is expressed in most vertebrate cells and tissues, it appears to be expressed at relatively low levels – on the order of hundreds or perhaps a few thousand copies per cell [5]. A short form of Myo10 is expressed in the brain [5]. Preliminary data indicate that this unusual isoform lacks most of the motor domain and is a nearly ‘headless’ myosin [24]. Interestingly, several proteins that

Localization of myosins to the tips of filopodia

One of the most intriguing features of Myo10 is its localization at the tips of filopodia (Figure 3) 5, 27. Filopodia are slender cellular extensions that contain a core of bundled actin filaments and appear to function as fingers or sensors that explore and interact with a cell's surroundings. Because filopodia and related structures, such as microvilli and stereocilia, grow by polymerization of actin at their tips, there is much interest in the molecular machinery that regulates

Intrafilopodial motility

Live-cell imaging in HeLa cells led to the discovery that GFP-Myo10 is present at the tips of filopodia during both extension and retraction [27]. This indicates that Myo10 either translocates along the actin filaments as quickly as they polymerize or is pushed ahead by the growing actin bundle. Importantly, in substrate-attached filopodia, puncta of GFP-Myo10 occasionally release from the tip and move rearward at 10–20 nm s⁻¹, which is the rate of retrograde actin flow in these filopodia. In

What do myosins do at the tips of filopodia?

The localization of Myo10 at the tips of filopodia and its filopodia-promoting effects raise the question of the role of myosins at the tips of filopodia. As discussed above, the forward intrafilopodial motility of Myo10 indicates that it might deliver materials that are required for filopodial extension. Another possibility is that myosin-generated forces directly facilitate actin polymerization at the tip by pushing the plasma membrane away from the barbed end, thus creating space to allow

Other MyTH-FERM myosins

In addition to Myo10, vertebrates express three other MyTH-FERM myosins: Myo7a, Myo7b and Myo15a [1]. Myo7a is the subject of intensive study because its mutation results in several forms of deafness including Usher Syndrome 1b, which is the most common form of hereditary deaf–blindness in humans [57]. Myo7a localizes along stereocilia (actin-based extensions that are similar to giant microvilli) in hair cells of the inner ear, and appears to have a role in linking the stereociliary plasma

Concluding remarks

Research with the MyTH-FERM myosins raises many questions for future study. What are the native structures of these proteins and the properties of their motor domains? Do MyTH-FERM myosins have key roles in the formation of actin bundles in structures such as filopodia, microvilli and stereocilia? If the filopodial-tip complex is a specialized site of polymerization, signaling and adhesion, what are its components, and how is it related to other adhesive structures such as focal adhesions and

Acknowledgements

AS was supported by NIH grant 1-P60-DE-13079 to the UNC Comprehensive Center for Inflammatory Disease and RC is supported by NIH/NIDCD grant DC03299.

References (75)

Z-Y. Chen
Myosin VIIb, a novel unconventional myosin, is a constituent of microvilli in transporting epithelia
Genomics
(2001)
S. Yonezawa
Mouse myosin X: molecular architecture and tissue expression as revealed by northern blot and in situ hybridization analyses
Biochem. Biophys. Res. Commun.
(2000)
K. Homma
Motor function and regulation of myosin X
J. Biol. Chem.
(2001)
M.S. Rogers et al.
The tumor-sensitive calmodulin-like protein is a specific light chain of human unconventional myosin x
J. Biol. Chem.
(2001)
M. Rechsteiner et al.
PEST sequences and regulation by proteolysis
Trends Biochem. Sci.
(1996)
F.I. Comer et al.
PI 3-kinases and PTEN: how opposites chemoattract
Cell
(2002)
G.I. Mashanov
The spatial and temporal dynamics of pleckstrin homology domain binding at the plasma membrane measured by imaging single molecules in live mouse myoblasts
J. Biol. Chem.
(2004)
Y. Liang
Characterization of the human and mouse unconventional myosin XV genes responsible for hereditary deafness DFNB3 and shaker 2
Genomics
(1999)
A.S. Reddy
A novel plant calmodulin-binding protein with a kinesin heavy chain motor domain
J. Biol. Chem.
(1996)
A.H. Chishti
The FERM domain: a unique module involved in the linkage of cytoplasmic proteins to the membrane
Trends Biochem. Sci.
(1998)

M.A. Pearson

Structure of the ERM protein moesin reveals the FERM domain fold masked by an extended actin binding tail domain

Cell

(2000)

K.S. Yan

PTB or not PTB–that is the question

FEBS Lett.

(2002)

I.D. Campbell et al.

The talin-tail interaction places integrin activation on FERM ground

Trends Biochem. Sci.

(2004)

X. Huang

MAX-1, a novel PH/MyTH4/FERM domain cytoplasmic protein implicated in netrin-mediated axon repulsion

Neuron

(2002)

M. Kovacs

Mechanism of action of myosin X, a membrane-associated molecular motor

J. Biol. Chem.

(2005)

T.D. Pollard et al.

Cellular motility driven by assembly and disassembly of actin filaments

Cell

(2003)

M.J. Tyska et al.

MYO1A (Brush Border Myosin I) Dynamics in the Brush Border of LLC-PK1-CL4 Cells

Biophys. J.

(2002)

N. Tang et al.

Motor domain-dependent localization of myo1b (myr-1)

Curr. Biol.

(2001)

H. Tokuo et al.

Myosin X transports Mena/VASP to the tip of filopodia

Biochem. Biophys. Res. Commun.

(2004)

J.E. Bear

Antagonism between Ena/VASP proteins and actin filament capping regulates fibroblast motility

Cell

(2002)

T. Mitchison et al.

Cytoskeletal dynamics and nerve growth

Neuron

(1988)

M.E. Ross

Classification of pediatric acute lymphoblastic leukemia by gene expression profiling

Blood

(2003)

M. Brajenovic

Comprehensive proteomic analysis of human Par protein complexes reveals an interconnected protein network

J. Biol. Chem.

(2004)

R.I. Tuxworth

A role for myosin VII in dynamic cell adhesion

Curr. Biol.

(2001)

M.A. Titus

A class VII unconventional myosin is required for phagocytosis

Curr. Biol.

(1999)

K. Homma et al.

Myosin-X is a high duty ratio motor

J. Biol. Chem.

(2005)

J.S. Berg

A millennial myosin census

Mol. Biol. Cell

(2001)

A. De Lozanne et al.

Disruption of the Dictyostelium myosin heavy chain gene by homologous recombination

Science

(1987)

C.K. Solc

Molecular cloning of myosins from the bullfrog saccular macula: a candidate for the hair cell adaptation motor

Aud. Neurosci.

(1994)

J.S. Berg

Myosin-X, a novel myosin with pleckstrin homology domains, associates with regions of dynamic actin

J. Cell Sci.

(2000)

S.J. Isakoff

Identification and analysis of PH domain-containing targets of phosphatidylinositol 3-kinase using a novel in vivo assay in yeast

EMBO J.

(1998)

D. Tacon

Imaging myosin 10 in cells

Biochem. Soc. Trans.

(2004)

L.C. Cantley

The phosphoinositide 3-kinase pathway

Science

(2002)

K.L. Weber

A microtubule-binding myosin required for nuclear anchoring and spindle assembly

Nature

(2004)

K. Hamada

Structural basis of the membrane-targeting and unmasking mechanisms of the radixin FERM domain

EMBO J.

(2000)

H. Zhang

Myosin-X provides a motor-based link between integrins and the cytoskeleton

Nat. Cell Biol.

(2004)

A.D. Sousa

Myosin-X in brain: developmental regulation, identification of a headless isoform, and dynamics in neurons

Mol. Biol. Cell

(2004)

Cited by (105)

MYH9: A key protein involved in tumor progression and virus-related diseases
2024, Biomedicine and Pharmacotherapy
The myosin heavy chain 9 (MYH9) gene encodes the heavy chain of non-muscle myosin IIA (NMIIA), which belongs to the myosin II subfamily of actin-based molecular motors. Previous studies have demonstrated that abnormal expression and mutations of MYH9 were correlated with MYH9-related diseases and tumors. Furthermore, earlier investigations identified MYH9 as a tumor suppressor. However, subsequent research revealed that MYH9 promoted tumorigenesis, progression and chemoradiotherapy resistance. Note-worthily, MYH9 has also been linked to viral infections, like severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), Epstein-Barr virus, and hepatitis B virus, as a receptor or co-receptor. In addition, MYH9 promotes the development of hepatocellular carcinoma by interacting with the hepatitis B virus-encoding X protein. Finally, various findings highlighted the role of MYH9 in the development of these illnesses, especially in tumors. This review summarizes the involvement of the MYH9-regulated signaling network in tumors and virus-related diseases and presents possible drug interventions on MYH9, providing insights for the use of MYH9 as a therapeutic target for tumors and virus-mediated diseases.
Length control of long cell protrusions: Rulers, timers and transport
2022, Physics Reports
Living cells use long tubular appendages for locomotion and sensory purposes. Hence, assembling and maintaining a protrusion of correct length is crucial for survival and overall performance. Usually the protrusions lack the machinery for the synthesis of building blocks and imports them from the cell body. What are the unique features of the transport logistics which facilitate the exchange of these building blocks between the cell and the protrusion? What kind of ‘rulers’ and ‘timers’ does the cell use for constructing its appendages of correct length on time? How do the multiple appendages coordinate and communicate among themselves during different stages of their existence? How frequently do the fluctuations drive the length of these dynamic protrusions out of the acceptable bounds? These questions are addressed from a broad perspective in this review which is organized in three parts. In part-I the list of all known cell protrusions is followed by a comprehensive list of the mechanisms of length control of cell protrusions reported in the literature. We review not only the dynamics of the genesis of the protrusions, but also their resorption and regrowth as well as regeneration after amputation. As a case study in part-II, the specific cell protrusion that has been discussed in detail is eukaryotic flagellum (also known as cilium); this choice was dictated by the fact that flagellar length control mechanisms have been studied most extensively over more than half a century in cells with two or more flagella. Although limited in scope, brief discussions on a few non-flagellar cell protrusions in part-III of this review is intended to provide a glimpse of the uncharted territories and challenging frontiers of research on subcellular length control phenomena that awaits rigorous investigations.
Application of piconewton forces to individual filopodia reveals mechanosensory role of L-type Ca<sup>2+</sup> channels
2022, Biomaterials
Filopodia are ubiquitous membrane projections that play crucial role in guiding cell migration on rigid substrates and through extracellular matrix by utilizing yet unknown mechanosensing molecular pathways. As recent studies show that Ca²⁺ channels localized to filopodia play an important role in regulation of their formation and since some Ca²⁺ channels are known to be mechanosensitive, force-dependent activity of filopodial Ca²⁺ channels might be linked to filopodia's mechanosensing function. We tested this hypothesis by monitoring changes in the intra-filopodial Ca²⁺ level in response to application of stretching force to individual filopodia of several cell types using optical tweezers. Results show that stretching forces of tens of pN strongly promote Ca²⁺ influx into filopodia, causing persistent Ca²⁺ oscillations that last for minutes even after the force is released. Several known mechanosensitive Ca²⁺ channels, such as Piezo 1, Piezo 2 and TRPV4, were found to be dispensable for the observed force-dependent Ca²⁺ influx, while L-type Ca²⁺ channels appear to be a key player in the discovered phenomenon. As previous studies have shown that intra-filopodial transient Ca²⁺ signals play an important role in guidance of cell migration, our results suggest that the force-dependent activation of L-type Ca²⁺ channels may contribute to this process. Overall, our study reveals an intricate interplay between mechanical forces and Ca²⁺ signaling in filopodia, providing novel mechanistic insights for the force-dependent filopodia functions in guidance of cell migration.
Squeezing in a Meal: Myosin Functions in Phagocytosis
2020, Trends in Cell Biology
Phagocytosis is a receptor-mediated, actin-dependent process of internalization of large extracellular particles, such as pathogens or apoptotic cells. Engulfment of phagocytic targets requires the activity of myosins, actin-dependent molecular motors, which perform a variety of functions at distinct steps during phagocytosis. By applying force to actin filaments, the plasma membrane, and intracellular proteins and organelles, myosins can generate contractility, directly regulate actin assembly to ensure proper phagocytic internalization, and translocate phagosomes or other cargo to appropriate cellular locations. Recent studies using engineered microenvironments and phagocytic targets have demonstrated how altering the actomyosin cytoskeleton affects phagocytic behavior. Here, we discuss how studies using genetic and biochemical manipulation of myosins, force measurement techniques, and live-cell imaging have advanced our understanding of how specific myosins function at individual steps of phagocytosis.
The Antiparallel Dimerization of Myosin X Imparts Bundle Selectivity for Processive Motility
2018, Biophysical Journal
Myosin X is an unconventional actin-based molecular motor involved in filopodial formation, microtubule-actin filament interaction, and cell migration. Myosin X is an important component of filopodia regulation, localizing to tips of growing filopodia by an unclear targeting mechanism. The native α-helical dimerization domain of myosin X is thought to associate with antiparallel polarity of the two amino acid chains, making myosin X the only myosin that is currently considered to form antiparallel dimers. This study aims to determine if antiparallel dimerization of myosin X imparts selectivity toward actin bundles by comparing the motility of parallel and antiparallel dimers of myosin X on single and fascin-bundled actin filaments. Antiparallel myosin X dimers exhibit selective processivity on fascin-bundled actin and are only weakly processive on single actin filaments below saturating [ATP]. Artificial forced parallel dimers of myosin X are robustly processive on both single and bundled actin, exhibiting no selectivity. To determine the relationship between gating of the reaction steps and observed differences in motility, a mathematical model was developed to correlate the parameters of motility with the biochemical and mechanical kinetics of the dimer. Results from the model, constrained by experimental data, suggest that the probability of binding forward, toward the barbed end of the actin filament, is lower in antiparallel myosin X on single actin filaments compared to fascin-actin bundles and compared to constructs of myosin X with parallel dimerization.
Competition between Coiled-Coil Structures and the Impact on Myosin-10 Bundle Selection
2016, Biophysical Journal
Citation Excerpt :
Myosin-10 transports several cell-surface receptors to filopodial tips in vertebrate cells (1–3).
Coiled-coil fusions are a useful approach to enforce dimerization in protein engineering. However, the final structures of coiled-coil fusion proteins have received relatively little attention. Here, we determine the structural outcome of adjacent parallel and antiparallel coiled coils. The targets are coiled coils that stabilize myosin-10 in single-molecule biophysical studies. We reveal the solution structure of a short, antiparallel, myosin-10 coiled-coil fused to the parallel GCN4-p1 coiled coil. Surprisingly, this structure is a continuous, antiparallel coiled coil where GCN4-p1 pairs with myosin-10 rather than itself. We also show that longer myosin-10 segments in these parallel/antiparallel fusions are dynamic and do not fold cooperatively. Our data resolve conflicting results on myosin-10 selection of actin filament bundles, demonstrating the importance of understanding coiled-coil orientation and stability.

View all citing articles on Scopus

View full text

Trends in Cell Biology

Myosin-X: a molecular motor at the cell's fingertips

Introduction

Section snippets

Discovery and structure of Myo10

Distribution and biochemical properties of Myo10

Localization of myosins to the tips of filopodia

Intrafilopodial motility

What do myosins do at the tips of filopodia?

Other MyTH-FERM myosins

Concluding remarks

Acknowledgements

Genomics

Biochem. Biophys. Res. Commun.

J. Biol. Chem.

J. Biol. Chem.

Trends Biochem. Sci.

Cell

J. Biol. Chem.

Genomics

J. Biol. Chem.

Trends Biochem. Sci.

Cell

FEBS Lett.

Trends Biochem. Sci.

Neuron

J. Biol. Chem.

Cell

Biophys. J.

Curr. Biol.

Biochem. Biophys. Res. Commun.

Cell

Neuron

Blood

J. Biol. Chem.

Curr. Biol.

Curr. Biol.

J. Biol. Chem.

A millennial myosin census

Mol. Biol. Cell

Disruption of the Dictyostelium myosin heavy chain gene by homologous recombination

Science

Molecular cloning of myosins from the bullfrog saccular macula: a candidate for the hair cell adaptation motor

Aud. Neurosci.

Myosin-X, a novel myosin with pleckstrin homology domains, associates with regions of dynamic actin

J. Cell Sci.

Identification and analysis of PH domain-containing targets of phosphatidylinositol 3-kinase using a novel in vivo assay in yeast

EMBO J.

Imaging myosin 10 in cells

Biochem. Soc. Trans.

The phosphoinositide 3-kinase pathway

Science

A microtubule-binding myosin required for nuclear anchoring and spindle assembly

Nature

Structural basis of the membrane-targeting and unmasking mechanisms of the radixin FERM domain

EMBO J.

Myosin-X provides a motor-based link between integrins and the cytoskeleton

Nat. Cell Biol.

Myosin-X in brain: developmental regulation, identification of a headless isoform, and dynamics in neurons

Mol. Biol. Cell