Structure of CYRI-B (FAM49B), a key regulator of cellular actin assembly.

Elise Kaplan,Rachael Stone,Nicholas P Greene,Peter J Hume,Vassilis Koronakis

doi:10.1107/s2059798320010906

Elise Kaplan, Rachael Stone + Show 3 more

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https://doi.org/10.1107/s2059798320010906

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Abstract

In eukaryotes, numerous fundamental processes are controlled by the WAVE regulatory complex (WRC) that regulates cellular actin polymerization, crucial for cell motility, cell-cell adhesion and epithelial differentiation. Actin assembly is triggered by interaction of the small GTPase Rac1 with CYFIP1, a key component of the WRC. Previously known as FAM49B, CYRI-B is a protein that is highly conserved across the Eukaryota and has recently been revealed to be a key regulator of Rac1 activity. Mutation of CYRI-B or alteration of its expression therefore leads to altered actin nucleation dynamics, with impacts on lamellipodia formation, cell migration and infection by intracellular pathogens. In addition, knockdown of CYRI-B expression in cancer cell lines results in accelerated cell proliferation and invasiveness. Here, the structure of Rhincodon typus (whale shark) CYRI-B is presented, which is the first to be reported of any CYRI family member. Solved by X-ray crystallography, the structure reveals that CYRI-B comprises three distinct α-helical subdomains and is highly structurally related to a conserved domain present in CYFIP proteins. The work presented here establishes a template towards a better understanding of CYRI-B biological function.

Highlights

Actin filament dynamics are central to a myriad of essential cellular processes such as cell migration, division and intracellular trafficking (Pollard & Cooper, 2009; Rottner et al, 2017; Rottner & Schaks, 2019)
The best-characterized nucleation-promoting factors (NPFs) are those belonging to the Wiskott–Aldrich syndrome protein (WASP) family, which stimulate Arp2/3 via C-terminal VCA domains (Pollitt & Insall, 2009; Alekhina et al, 2017)
We attempted to solve the structure by molecular replacement using the DUF1394 domain of CYFIP1 (PDB entry 3p8c; Chen et al, 2010), as it shares 21% sequence identity with whale shark CYRI-B and is predicted to be structurally similar (Yuki et al, 2019)

Summary

Introduction

Actin filament dynamics are central to a myriad of essential cellular processes such as cell migration, division and intracellular trafficking (Pollard & Cooper, 2009; Rottner et al, 2017; Rottner & Schaks, 2019). Actin assembly is nucleated by cellular machines such as the ubiquitous Arp2/3 complex, which drives the generation of the branched actin networks underlying processes including lamellipodia formation and cell motility (Buracco et al, 2019). The best-characterized NPFs are those belonging to the Wiskott–Aldrich syndrome protein (WASP) family, which stimulate Arp2/3 via C-terminal VCA (verprolin-homology, central and acidic regions) domains (Pollitt & Insall, 2009; Alekhina et al, 2017). The WASP family members WAVE1, WAVE2 and WAVE3 are central to cell motility and protrusion formation (Kurisu & Takenawa, 2009; Rottner & Schaks, 2019), and each functions as part of a heteropentameric complex termed the WAVE regulatory complex (WRC; Chen et al, 2010, 2014).

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