STRUCTURE/FUNCTION RELATIONSHIP STUDY OF GLN156, GLU160 AND GLU189 IN THE ACTIVE-SITE OF TRICHOSANTHIN
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摘要Trichosanthin is a protein used medicinally in China for abortifacient purposes. It is also an RNA N-glycosidase which inactivates eukaryotic ribosomes by removing adenine4324 from 28S rRNA. Site-directed mutagenesis was performed to probe the role of Gln156, Glu160 and Glu189 in the active site of trichosanthin. The purified altered proteins were assayed for their potency in inhibiting in vitro protein synthesis. The data indicate Glu160 is involved in the catalytic reaction. Kinetics studies suggest the carboxylate group of Glu160 serves to stabilize the transition-state complex. Similar to ricin A, the variant [E160A]trichosanthin is more potent than [E160D]trichosanthin. This is because Glu189 serves as a back-up of the carboxylate group in case Glu160 is mutated to alanine. However, removal of Glu189 in the presence of Glu160 does not affect the ID50 value drastically. An activity of 1800-fold less than that of the wild-type protein was found when both Glu160 and Glu189 were changed to alanine, indicating that some other residues in the active site are also taken part in the lowering of energy barrier for the catalytic reaction. Although Gln156 is highly conserved in related proteins, its mutation to alanine only slightly decreases the activity, showing that this residue does not participate directly in catalysis.
著者WONG KB, KE YB, DONG YC, LI XB, GUO YW, YEUNG HW, SHAW PC
期刊名稱European Journal of Biochemistry
出版年份1994
月份4
日期15
卷號221
期次2
出版社SPRINGER VERLAG
頁次787 - 791
國際標準期刊號0014-2956
語言英式英語
Web of Science 學科類別Biochemistry & Molecular Biology

上次更新時間 2020-20-10 於 03:08