Abstract
Ricin A-chain, abrin A-chain, and alpha-trichosanthin are members of a larger group of proteins called ribosome-inactivating proteins. These proteins all function to catalytically inactivate eukaryotic 60 S ribosomal subunits leading to rapid shutdown of protein synthesis. They are homologous in sequence and are probably evolutionarily related. We have determined the complete primary amino acid sequence of alpha-trichosanthin and have found it to be homologous, as expected, to that of abrin A-chain and ricin A-chain. A crystal structure for ricin, which includes ricin A-chain and ricin B-chain, has been determined from x-ray diffraction data. Based on the sequence homologies of these proteins, we fit the primary sequences of abrin A-chain and alpha-trichosanthin to the backbone structure for ricin A-chain and have generated energy-minimized molecular models for them. These models should prove useful in studying the structural-functional relationships of these proteins in particular and of the class in general.
Highlights
From the *Department of Chemistry, University of Texas, Austin, Texas 78712, the SDepartment of Molecular Biophysics and Biochemistry, Yale University School of Medicine, New Haven, Connecticut 06510, and TGenelabs Incorporated, Redwood City, California 94063
Ricin A-chain, abrin A-chain, and a-trichosanthin are members of a larger group of proteins called ribosome-inactivating proteins. These proteins all function to catalytically inactivate eukaryotic 60 S ribosomal subunits leading to rapid shutdown of protein synthesis
Ribosome inactivating proteins (RIPS)’ form a large and widely distributed class of proteins in higher plants. These proteins are potent inhibitors of eukaryotic protein synthesis. They catalytically cleave the N-glycosidic bond of a specific adenine nucleoside residue in 28 S rRNA, A4324 in rat liver rRNA, thereby impairing the ability of elongation factor 2 to bind to the eukaryotic 60 S ribosomal subunit [4,5,6,7,8]
Summary
Purification and Amino Acid Sequencing of cu-TCS-Frozen root tubers of T. kirilowii Maximowicz were obtained from the Canton region in Southern China. Lys-C digest was carried out on 30 nmol of protein as previously described [31] using 0.003 units of enzyme per pg of protein. The amino acid sequences of abrA and Stereochemical clashes resulting from the amino acid changes were initially adjusted by hand on the graphic system, maintaining as much of the ricA geometry as possible. Jones potential were carried out until the overall energy for each model changed by less than 10 kJ per mol This required 200 and 300 cycles for abrA and a-TCS, respectively
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