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bioRxiv · 10.1101/2023.08.14.553178

Structure and activation mechanism of the Makes caterpillars floppy 1 toxin

Belyy, A.·Heilen, P.·Hagel, P.·Hofnagel, O.·Raunser, S.
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Abstract

The bacterial Makes caterpillars floppy 1 (Mcf1) toxin promotes apoptosis in insects, leading to loss of body turgor and death. The molecular mechanism underlying Mcf1 intoxication is poorly understood. Here, we present the cryo-EM structure of Mcf1 from Photorhabdus luminescens, revealing a seahorse-like shape with a head and tail. While the three head domains contain two effectors, an activator-binding domain (ABD) and an autoprotease, the tail consists of two translocation as well as three receptor-binding domains. Rearrangement of the tail moves the C-terminus away from the ABD and allows binding of the host cell ADP-ribosylation factor 3, inducing conformational changes that position the cleavage site closer to the protease. This unique activation mechanism that is based on a hook-loop interaction results in three autocleavage reactions and the release of two toxic effectors. Unexpectedly, the BH3-like domain containing ABD is not an active effector. Our findings allow us to understand key steps of Mcf1 intoxication at the molecular level.

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Belyy, A., Heilen, P., Hagel, P., Hofnagel, O., Raunser, S.. 2023-08-14. Structure and activation mechanism of the Makes caterpillars floppy 1 toxin. https://doi.org/10.1101/2023.08.14.553178

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