The impact of cryosolution thermal contraction on proteins and protein crystals: volumes, conformation and order

Abstract

Cryosolution thermal contraction is found to have an impact on cryocooled protein and unit-cell volumes and conformations. In some cases, its adjustment can produce higher quality diffraction data.

Solvent flows, conformation changes and lattice reordering in a cold protein crystal

“…There is a reliable correlation between unit-cell contraction on cooling and the bulk contraction of the solution in which the crystals are grown or soaked. Juers and coworkers observed a near-linear relation between unit-cell contraction between room temperature and T = 100 K and the bulksolvent contraction in eight different protein crystal systems (Juers et al, 2018). The present data for apoferritin in Fig.…”

“…Direct efforts to demonstrate a relation between cold crystal mosaicity and the expected contraction of the internal solvent on cooling between room temperature and T = 77 or 100 K have so far yielded unconvincing results. Juers et al (2018) found no clear variation of mosaicity with bulk-solvent contraction for ice-free crystals of at least seven out of nine different protein crystal systems; only -lactalbumin showed weakly suggestive evidence of a mosaicity minimum versus unit-cell contraction. However, in these careful experiments any trends may have been obscured by the relatively large lower bound on measurable mosaicity owing to the large incident beam divergence of the laboratory X-ray source used.…”

“…Between 300 and 240 K liquid water expands by 2% (Hare & Sorensen, 1987) and a 40%(v/v) glycerol solution contracts by 2% (Glycerine Producers Association, 1963). This suggests that solvent must be expelled from or flow into the unit cell to account for the difference between the solvent-cavity and solvent contractions (Juers & Matthews, 2001, 2004Kriminski et al, 2002;Tyree et al, 2018;Juers et al, 2018). As shown in Supplementary Fig.…”

“…Ice formed within the solvent cavities of the unit cell can cause unit-cell expansion. Ice formed at crystal surfaces draws water from the rest of the crystal for its growth, and can cause unit cells to shrink (Juers et al, 2018), just as ice formed in intercellular spaces leads to cellular dehydration in biological cryopreservation (Fahy & Wowk, 2015).…”

“…The present results provide the clearest evidence to date for the role of solvent flows in causing cooling-induced disorder in protein crystals. During cooling, the unit-cell volume generally contracts more than the protein volume, so that the solventcavity volume shows the largest fractional decrease (Juers & Matthews, 2001, 2004Juers et al, 2018). Unless the solvent internal to the crystal contains large cryoprotectant concentrations [$30%(v/v) or more], its volume will contract less than the solvent cavities.…”