Photoactivatable Rac1: a photosensor tilt by time-resolved crystallography and a partially open switch I when GDP-bound

The LOV2 domain of Avena sativa phototropin 1 is widely used to control proteins with light, but how its signal reaches a fused effector has not been visualized. We followed photoactivatable Rac1 by time-resolved serial crystallography at room temperature. Within 350 µs, a fifth of the photosensors form the flavin–cysteine adduct and tilt as a rigid body on Rac1 about an axis through the domain interface, while the Jα helix stays docked and Rac1 keeps GTP and dark-state switches up to 1.85 ms. Dark crystals contain a variable GDP-bound sub-population, so light data must be referenced to interleaved dark frames. In this sub-population, switch I is only partially open, held at a Ca 2+ ion that bridges LOV2 and Rac1, a conformation that can persist in simulations without the lattice. The photosensor thus first acts on Rac1 at the interface that also holds switch I in the GDP-bound state.

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Publication Details

Journal
bioRxiv (Cold Spring Harbor Laboratory)
Published
2026-10-28
DOI
https://doi.org/10.64898/2026.10.27.762334
Primary Topic
Protein Kinase Regulation and GTPase Signaling
Type
preprint

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preprint

Photoactivatable Rac1: a photosensor tilt by time-resolved crystallography and a partially open switch I when GDP-bound

Thomas Ursby, Magdalena Pachota, Monika Bjelčić, Mirko Milas et al.
1 links
bioRxiv (Cold Spring Harbor Laboratory)
Protein Kinase Regulation and GTPase Signaling
preprint

Photoactivatable Rac1: a photosensor tilt by time-resolved crystallography and a partially open switch I when GDP-bound

Thomas Ursby, Magdalena Pachota, Monika Bjelčić, Mirko Milas, Przemysław Nogły, Aleksandra Solecka, Sofia M. Kapetanaki, Edina Rosta, Manoop Chenchiliyan, Cecilia Maria Casadei, Bence Olasz, M. Wisniewska, Larissa Lopes Cavalcante, Jie Nan, Anna Koczurowska, Madan Kumar Shankar, Ayesha Asghar, Ran Ke, Dean Lang
preprint en

Abstract

The LOV2 domain of Avena sativa phototropin 1 is widely used to control proteins with light, but how its signal reaches a fused effector has not been visualized. We followed photoactivatable Rac1 by time-resolved serial crystallography at room temperature. Within 350 µs, a fifth of the photosensors form the flavin–cysteine adduct and tilt as a rigid body on Rac1 about an axis through the domain interface, while the Jα helix stays docked and Rac1 keeps GTP and dark-state switches up to 1.85 ms. Dark crystals contain a variable GDP-bound sub-population, so light data must be referenced to interleaved dark frames. In this sub-population, switch I is only partially open, held at a Ca 2+ ion that bridges LOV2 and Rac1, a conformation that can persist in simulations without the lattice. The photosensor thus first acts on Rac1 at the interface that also holds switch I in the GDP-bound state.

bioRxiv (Cold Spring Harbor Laboratory)
Jagiellonian University (PL), MAX IV Laboratory (SE), University College London (GB)
European Synchrotron Radiation Facility, VINNOVA, Svenska Forskningsrådet Formas, Max-Planck-Gesellschaft, Novo Nordisk, Vetenskapsrådet, Engineering and Physical Sciences Research Council, Deutsches Elektronen-Synchrotron
Protein Kinase Regulation and GTPase Signaling
DOIOpen Access PDFOpenAlex
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