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

Authors

Pachota, M., Shankar, M. K., Wisniewska, M., Koczurowska, A., Casadei, C. M., Solecka, A., Kapetanaki, S. M., Olasz, B., Lopes Cavalcante, L., Ke, R., Lang, D., Bjelcic, M., Asghar, A., Milas, M., Ursby, T., Chenchiliyan, M., Nan, J., Rosta, E., Nogly, P.

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 {micro}s, 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 J 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 Ca2+ 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.

Preprint server: bioRxiv
The authors list and abstract were imported from bioRxiv on 29 Oct 2026.

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