The C-terminal tail extension of myosin 16 acts as a molten globule, including intrinsically disordered regions, and interacts with the N-terminal ankyrin

Elek Telek,Kristóf Karádi,József Kardos,András Kengyel,Zsuzsanna Fekete,Henriett Halász,Miklós Nyitrai,Beáta Bugyi,András Lukács

doi:10.1016/j.jbc.2021.100716

Elek Telek, Kristóf Karádi + Show 7 more

Open Access

https://doi.org/10.1016/j.jbc.2021.100716

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Abstract

The lesser-known unconventional myosin 16 protein is essential in proper neuronal functioning and has been implicated in cell cycle regulation. Its longer Myo16b isoform contains a C-terminal tail extension (Myo16Tail), which has been shown to play a role in the neuronal phosphoinositide 3-kinase signaling pathway. Myo16Tail mediates the actin cytoskeleton remodeling, downregulates the actin dynamics at the postsynaptic site of dendritic spines, and is involved in the organization of the presynaptic axon terminals. However, the functional and structural features of this C-terminal tail extension are not well known. Here, we report the purification and biophysical characterization of the Myo16Tail by bioinformatics, fluorescence spectroscopy, and CD. Our results revealed that the Myo16Tail is functionally active and interacts with the N-terminal ankyrin domain of myosin 16, suggesting an intramolecular binding between the C and N termini of Myo16 as an autoregulatory mechanism involving backfolding of the motor domain. In addition, the Myo16Tail possesses high structural flexibility and a solvent-exposed hydrophobic core, indicating the largely unstructured, intrinsically disordered nature of this protein region. Some secondary structure elements were also observed, indicating that the Myo16Tail likely adopts a molten globule–like structure. These structural features imply that the Myo16Tail may function as a flexible display site particularly relevant in post-translational modifications, regulatory functions such as backfolding, and phosphoinositide 3-kinase signaling.

Highlights

Myosins form a large and versatile superfamily of actinbased motor proteins that convert the chemical energy of ATP hydrolysis into mechanical force required for motion along actin filaments [1]
myosin 16 (Myo16) is a component of the neuronal phosphoinositide 3-kinase (PI3K) signaling pathway, in which it is phosphorylated by the Src family of tyrosine kinase Fyn at its C-terminal tail [17]
Myo16Tail (1146–1912 amino acids, Rattus norvegicus, UniProt: Q9ERC1) consists of the 30 amino acids of an IQ motif, an neuronal tyrosine-phosphorylated adaptor for PI3K homology motif (NHM) which is important in the neuronal PI3K signaling pathway, a Pro-rich region, and a very C-terminal sequence element (Fig. 1)

Summary

Introduction

Myosins form a large and versatile superfamily of actinbased motor proteins that convert the chemical energy of ATP hydrolysis into mechanical force required for motion along actin filaments [1] They are expressed in all eukaryotic organisms [2] and play essential roles in a variety of cellular processes, including organelle trafficking, cytokinesis, cell shape maintenance, or muscle contraction [3,4,5,6,7]. Some myosin tails contain α-helical regions and can form coiled-coil structure, allowing the myosin to dimerize [9], whereas other myosins are monomers containing functional domains, for example, Src homology 3, GTPase-activating protein, four-point-one, ezrin, radixin, moesin, or pleckstrin homology domains on their tail [10]. Genetic alterations of MYO16 were found to be involved in neurodegenerative disorders, including schizophrenia, autism spectrum disorder, bipolar disorder subtype II, and major depressive disorder [21,22,23], which underlines its important role in the proper functioning of the nervous system

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