Crystal structure of R22L trichosanthin

Crystals of R22L TCS were grown by vapour diffusion method. X-ray diffraction data were collected to 0.191 nm resolution on a Siemens X-200B area detector. The XENGEN programme was applied to data processing; the data were used to 0.22 nm. The structure was detcrmined by the difference Fourier method and refined using X-PLOR programme. The finalR factor was 0.182. The rms deviation of bond length and bond angle were 0.0013 nm and 2.770° respectively. In R22L TCS, two water molecules occupy the space left by Arg changed to Leu. The side chain of Gin168 rotates abut 50°. The OE2 atom of Glu168 links to the NZ atom of Lya165 through water molecule. The new hydrogen bond net partially replaces the Arg22 function. The effect of the conservative hydrogen bonds btween secondary structures on the conformation of active pocket was discussed. Project supported by the National Natural Science Foundation of China (Grant No. 39680003) and the Research Grants Council of Hung Kong.