POLARIS : The France Cryo-EM Titan KRIOS at SOLEIL.
POLARIS, the Titan KRIOS Cryo-electron microscope installed at SOLEIL, in the context of the project France Cryo-EM, is open to users via a ‘rolling access’ mechanism incorporated into the SOLEIL User Office Software (https://sun.synchrotron-soleil.fr/sunset/bridge/sunset/). Proposals can be submitted continuously, but are examined every 2 months by the peer review panel for Biology and Health (https://www.synchrotron-soleil.fr/fr/espace-utilisateurs/appel-projet-en-cours/comites-de-programmes-et-evaluation-des-projets). The first peer-reviewed user project took place in January 2025 (https://intranet.synchrotron-soleil.fr/fr/actualites/premiers-utilisateurs-pour-polaris-le-cryo-microscope-electronique-de-soleil). The microscope is currently operational and providing 3-4 days per week of peer reviewed access time. This is expected to increase to 4- 5 days per week in 2026.
Contacts
Pierre Legrand (SOLEIL)
Facility Manager
Eric Larquet (CNRS/I2BC)
Operation Manager
Heddy Soufari (CEA/I2BC)
Microscope Scientist
Andrew Thompson
Microscope Operator
Contact :
prenom.nom@synchrotron-soleil.fr
HIGHLIGHTS
1. Site acceptance tests demonstrate 1.14 Angstrom resolution from apo-ferritin test.
During 2024, a custom built room for the microscope was constructed in the SOLEIL experimental area. Much effort was spent in ensuring a suitable environment for the KRIOS, including electromagnetic field correction (to ensure that the microscope can operate independently to the synchrotron operation), very high temperature stability with very low cooling air flow rates (± 0.1 ° over 24 hours operation, with flow rates close to the microscope around 0.15 m s-1), and excellent vibrational stability ensure by the experimental hall floor of SOLEIL. Site tests on apo-ferritin, the protein regularly used as a standard for benchmarking microscope performance, see for example Stark et al, Nature 587 (2020), yielded 1.14 Angstrom resolution, hence demonstrating the high stability of the microscope environment.
2. High resolution structure of a membrane bound flippase.
The first user experiment was performed by the group of Thibaud DIeudonne (I2BC, Gif sur Yvette, (https://intranet.synchrotron-soleil.fr/fr/actualites/premiers-utilisateurs-pour-polaris-le-cryo-microscope-electronique-de-soleil), who performed an experiment comparing the attainable resolution for the same sample on a GLACIOS 2 microscope (https://www.i2bc.paris-saclay.fr/structural-biology/) and POLARIS. A publication outlining the results of this experiment is in preparation. Data collected on POLARIS achieved a record resolution of 2.16 Angstrom for this protein sample.
