Novel versatile cryoprotectants for heavy-atom derivatization of protein crystals

Determination of a suitable cryoprotectant agent condition is one of the time-consuming processes in protein X-ray crystallography. The adaptability of two novel versatile cryoprotectants (oil- and water-based types) has been evaluated by cryodiffraction experiments using crystals of five different proteins. The results suggest that complementary use of both oil- and water-based cryoprotectants enables the successful cryoprotection of protein crystals. Since the versatile cryoprotectants do not contain crystallization solution, rapid and efficient preparation of heavy-atom derivatives is possible with these cryoprotectants in the presence of heavy-atom reagents. Four heavy-atom reagents [K₂PtCl₄, HgCl₂, KAu(CN)₂ and K₂Pt(CN)₄] were examined and could be stored with sufficient derivatizing capabilities for over one month in the versatile cryoprotectants.