Structural Basis of CYRI-B Direct Competition with Scar/WAVE Complex for Rac1

Tamas Yelland,Anh Hoang Le,Savvas Nikolaou,Robert Insall,Laura Machesky,Shehab Ismail

doi:10.1016/j.str.2020.11.003

Tamas Yelland, Anh Hoang Le + Show 4 more

Open Access

https://doi.org/10.1016/j.str.2020.11.003

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Abstract

SummaryRac1 is a major regulator of actin dynamics, with GTP-bound Rac1 promoting actin assembly via the Scar/WAVE complex. CYRI competes with Scar/WAVE for interaction with Rac1 in a feedback loop regulating actin dynamics. Here, we reveal the nature of the CYRI-Rac1 interaction, through crystal structures of CYRI-B lacking the N-terminal helix (CYRI-BΔN) and the CYRI-BΔN:Rac1Q61L complex, providing the molecular basis for CYRI-B regulation of the Scar/WAVE complex. We reveal CYRI-B as having two subdomains - an N-terminal Rac1 binding subdomain with a unique Rac1-effector interface and a C-terminal Ratchet subdomain that undergoes conformational changes induced by Rac1 binding. Finally, we show that the CYRI protein family, CYRI-A and CYRI-B can produce an autoinhibited hetero- or homodimers, adding an additional layer of regulation to Rac1 signaling.

Highlights

Regulation of the cytoskeleton has a direct impact on cellular shape, polarity, migration, and homeostasis
A novel effector of Rac1, Fam49B known as CYRI-B (CYFIP-related Rac interactor), has been reported to bind to active Rac1 and oppose the activation of the Scar/WAVE complex (Fort et al, 2018)
We conclude that the DUF1394 domain of CYRI-B binds Rac1 through a unique effector-binding interface and we identify residues involved in this interaction, suggesting a model for how the DUF1394 domain interacts with active Rac1

Summary

Introduction

Regulation of the cytoskeleton has a direct impact on cellular shape, polarity, migration, and homeostasis. A novel effector of Rac, Fam49B known as CYRI-B (CYFIP-related Rac interactor), has been reported to bind to active Rac and oppose the activation of the Scar/WAVE complex (Fort et al, 2018) It was described as a local inhibitor of branched actin assembly, and is thought to be recruited by the activating signal-active Rac1-and suppresses Scar/WAVE activity (Fort et al, 2018). CYRI-B, its isoform CYRI-A and the Scar/WAVE complex all possess an evolutionarily conserved Rac binding domain (RBD) termed the DUF1394 domain Based on this homology, CYRI’s suppression of Rac1-mediated actin polymerization was proposed to be through direct competition with the Scar/ WAVE complex (Fort et al, 2018). The structural basis of this interaction and the interplay with Scar/WAVE binding are not known

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