The Structure of Trichosanthin with Space Group C2 at 1. 9 Resolution

1INTRODUCTIoNInrecentyears,researchesontheribosome-inactivatingproteins(RIPs)ex-tractedfromplantshavedrawnconsiderableattentionduetotheirhighlyspecialRNAN-glycosidaseactivityandtheiranti-HlVactivity"~".Theseproteinsinacti-vateenzymicallythelargesubunitofthemammalianribosomebythereleaseofA4324fromthe28Sr-RNAt4i.lthasbeenreportedthattheseproteinsalsoactonbac-terialandplantribosomes.Theirisolationandpurificationhavebeenstudiedinde-tail,andtheirpresentstatusandfutureprospectshavealsobeen…

The Structure of Trichosanthin with Space Group C2 at 1. 9 Resolution

The crystal structure of trichosanthin (TCS) in space group C2 hasbeen refined by PROLSQ and XPLOR to an R-factor of 0. 204 for 33, 531 reflectionswith F。≥2-σ(F。) between 6 to 1. 9 A resolution. The root mean square(r. m. s. ) devi-ations of bond lengths and bond angles from the standard values are 0. 015 A and 2.77°, respectively. The overall fold of the molecule of TCS is, in general, similar to oth-er RIPs, but there are some differences in secondary structure and in the active sitecleft. An overlay of the two molecules (shown by Mol. A and Mol. B), which are notrelated by symmetry in an asymmetric unit, results in an r. m. s. deviation of 0. 850Afor the main chain atoms. The backbones of the C-terminus of the two molecules arequite different. The structures of the water in two molecules are not completely analo-gous. In the active site cleft of Mol. B, the bonding sites of three water molecules toprotein are similar to those of N atoms of formycin ring in the structure of pokeweedantiviral protein complexed with formycin 5-monophosphate, and the side chains of twoTyr70 in the two crystalline forms of TCS show a similar orientation, which is differentfrom that of the corresponding residue in ricin A-chain.