Xenon pressurisation and diffraction data recording

Crystals of both forms were fished out from drops using Hampton® cryoloops and were pressurized in a XCell® from Oxford Cryosystems at a standard pressure of 2 MPa of xenon. After about 5 min, the pressure was released and the loop immediately plunged in liquid nitrogen for quenching. It was known from earlier studies that GLIC crystals do not diffract equally, even coming out from the same drop of crystallization. We thus selected about ten crystals of each form to be exposed to xenon according to the above-described protocol. The best diffracting crystal was selected for diffraction recordings by analysing a single test frame.

Data recordings were conducted at the ESRF synchrotron (Grenoble, France) for the open form of GLIC (beam line BM30A) and at SOLEIL synchrotron (Gif-sur-Yvette, France) for the LC form of GLIC (beam line PROXIMA-1). Wavelengths were chosen within the range 1.1–1.3 Å as a compromise between a significant anomalous signal for xenon and the deleterious effects of absorption. The two data sets of frames were processed using XDS [52]. The resulting independent structure factor amplitudes were formatted using the CCP4 package of programs [53]. The different parameters and statistics of the recording conditions are reported in the Table 1.

* From Luzzati plots

# 100^th percentile is the best among structures of comparable resolution

Values in parenthesis are for the highest resolution shell