The crystal structure of abrin-a, a type II ribosome-inactivating protein from the seeds of Abrus precatorius, has been determined from a novel crystalline form by the molecular replacement method using the coordinates of ricin. The structure has been refined at 2 ...
The crystal structure of abrin-a, a type II ribosome-inactivating protein from the seeds of Abrus precatorius, has been determined from a novel crystalline form by the molecular replacement method using the coordinates of ricin. The structure has been refined at 2.14 A to a R-factor of 18.9%. The root-mean-square deviations of bond lengths and angles from the standard values are 0.013 A and 1.82 degrees, respectively. The overall protein folding is similar to that of ricin, but there are differences in the secondary structure, mostly of the A-chain. Several parts of the molecular surface differ significantly; some of them are quite near the active site cleft, and probably influence ribosome recognition. The positions of invariant active site residues remain the same, except the position of Tyr74. Two water molecules of hydrogen-bonded active site residues have been located in the active site cleft. Both of them may be responsible for hydrolyzing the N-C glycosidic bond. The current abrin-a structure is lactose free; this is probably essential for abrin-a crystallization. The B-chain is a glycoprotein, and the positions of several sugar residues of two sugar chains linked to earlier predicted glycosylation sites were determined. One of the sugar chains is a bridge between two neighboring molecules, since one of its mannose residues is connected to the galactose binding site of the neighboring molecule. Another sugar chain covers the surface of the B-chain.
Related Citations:
A New Crystal Form of Abrin-A from the Seeds of Abrus Precatorius Tahirov, T.H., Lu, T.-H., Liaw, Y.-C., Chu, S.-C., Lin, J.-Y. (1994) J Mol Biol 235: 1152
Primary Structure of Three Distinct Isobrins Determined by Cdna Sequencing: Conservation and Significance Hung, C.-H., Lee, M.-C., Lee, T.-C., Lin, J.-Y. (1993) J Mol Biol 229: 263
The Complete Amino Acid Sequence of the A-Chain of Abrin-1, a Toxic Protein from the Seeds of Abrus Precatorius Fanatsu, G., Taguchi, Y., Kamenosono, M., Yanaka, M. (1988) J Biol Chem 52: 1095
Organizational Affiliation:
Department of Physics, National Tsing Hua University, Hsinchu, Taiwan, Republic of China.
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