The crystal structure of chicken egg white cystatin has been solved by X-ray diffraction methods using the multiple isomorphous replacement technique. Its structure has been refined to a crystallographic R value of 0.19 using X-ray data between 6 and ...
The crystal structure of chicken egg white cystatin has been solved by X-ray diffraction methods using the multiple isomorphous replacement technique. Its structure has been refined to a crystallographic R value of 0.19 using X-ray data between 6 and 2.0A. The molecule consists mainly of a straight five-turn alpha-helix, a five-stranded antiparallel beta-pleated sheet which is twisted and wrapped around the alpha-helix and an appending segment of partially alpha-helical geometry. The 'highly conserved' region from Gln53I to Gly57I implicated with binding to cysteine proteinases folds into a tight beta-hairpin loop which on opposite sides is flanked by the amino-terminal segment and by a second hairpin loop made up of the similarly conserved segment Pro103I - Trp104I. These loops and the amino-terminal Gly9I - Ala10I form a wedge-shaped 'edge' which is quite complementary to the 'active site cleft' of papain. Docking experiments suggest a unique model for the interaction of cystatin and papain: according to it both hairpin loops of cystatin make major binding interactions with the highly conserved residues Gly23, Gln19, Trp177 and Ala136 of papain in the neighbourhood of the reactive site Cys25; the amino-terminal segment Gly9I - Ala10I of bound cystatin is directed towards the substrate subsite S2, but in an inappropriate conformation and too far away to be attacked by the reactive site Cys25. As a consequence, the mechanism of the interaction between cysteine proteinases and their cystatin-like inhibitors seems to be fundamentally different from the 'standard mechanism' defined for serine proteinases and most of their protein inhibitors.
Related Citations:
Conformational Variability of Chicken Cystatin: Comparison of Structures Determined by X-Ray Diffraction and NMR-Spectroscopy Engh, R.A., Dieckmann, T., Bode, W., Auerswald, E.A., Turk, V., Huber, R., Oschkinat, H. (1993) J Mol Biol 234: 1060
The Structures of Native Phosphorylated Chicken Cystatin and of a Recombinant Unphosphorylated Variant in Solution Dieckmann, T., Mitschang, L., Hofmann, M., Kos, J., Turk, V., Auerswald, E.A., Jaenicke, R., Oschkinat, H. (1993) J Mol Biol 234: 1048
The Cystatins: Protein Inhibitors of Cysteine Proteinases Turk, V., Bode, W. (1991) FEBS Lett 285: 213
Mechanism of Interaction of Cysteine Proteinases and Their Protein Inhibitors as Compared to the Serine Proteinase-Inhibitor Interaction Bode, W., Engh, R., Musil, D., Laber, B., Stubbs, M., Huber, R., Turk, V. (1990) Biol Chem Hoppe Seyler 371: 111
Mechanism of Inhibition of Papain by Chicken Egg White Cystatin: Inhibition Constants of N-Terminally Truncated Forms and Cyanogen Bromide Fragments of the Inhibitor Machleidt, W., Thiele, U., Laber, B., Assfalg-Machleidt, I., Esterl, A., Wiegand, G., Kos, J., Turk, V., Bode, W. (1989) FEBS Lett 243: 234
The Cysteine Proteinase Inhibitor Chicken Cystatin is a Phophoprotein Laber, B., Krieglstein, K., Henschen, A., Kos, J., Turk, V., Huber, R., Bode, W. (1989) FEBS Lett 248: 162
Organizational Affiliation:
Max-Planck-Institut für Biochemie, Martinsried, FRG.
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