High-pressure cryocooling for capillary sample cryoprotection and diffraction phasing at long wavelengths.

Crystal cryocooling is usually employed to reduce radiation damage during X-ray crystallography. Recently, a high-pressure cryocooling method has been developed which results in excellent diffraction-quality crystals without the use of penetrative cryoprotectants. Three new developments of the method are presented here: (i) Xe-He high-pressure cryocooling for Xe SAD phasing, (ii) native sulfur SAD phasing and (iii) successful cryopreservation of crystals in thick-walled capillaries without additional cryoprotectants other than the native mother liquor. These developments may be useful for structural solution of proteins without the need for selenomethionine incorporation and for high-throughput protein crystallography.