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The three-dimensional structure of trichosanthin crystallizing in space group C2 has beenrefined at 2.7 resolution from a previously reported starting model at 3 resolution based on asolvent flattened map and the revised primary structure consisting of 247 amlno-acids.The finalR-factor is 19.2% with the root mean-square deviations of 0.018 from ideal bond lengths andof 2.2° from ideal bond angles.Trichosanthin molecule is composed of two domains,the largedomain consisting of 181 amino-acld residues starting from N-terminus and the small domain con-sisting of the rest of the amino-acid residues.The molecule contains eight α-helices,five β-sheetsmade of sixteen β-strands,and some reverse turns.It is noteworthy that some of the α-helicesand β-sheets show irregular hydrogen bonding patterns.Six of the thirteen residues absolutelyconserved in eleven ribosome-inactivating proteins are located in a cleft near the interface ofthe two domains and they are likely to be active sites.Three additional conservative residueslocated in the cleft region might make some functional contribution as well.
The three-dimensional structure of trichosanthin crystallizing in space group C2 has been refined at 2.7 resolution from a previously reported starting model at 3 resolution based on asconvent flattened map and the revised primary structure consisting of 247 amlno-acids. The final R-factor is 19.2% with the root mean-square deviations of 0.018 from ideal bond lengths and of 2.2 ° from ideal bond angles. Trichosanthin molecule is composed of two domains, the large domain consisting of 181 amino-acld residues starting from N-terminus and the small domain con-sisting of the rest of the amino-acid residues. The molecule contains eight α-helices, five β-sheets made of sixteen β-strands, and some reverse turns. It is noteworthy that some of the α-helices and β-sheets show irregular hydrogen bonding patterns.Six of the thirteen residues absolutely conserved in eleven ribosome-inactivating proteins are located in a cleft near the interface of the two domains and they are likely to be active sites.Thre e additional conservative residueslocated in the cleft region might make some functional contribution as well.