CRYSTAL-STRUCTURE OF A PROTEIN-TOXIN ALPHA-1-PUROTHIONIN AT 2.5A AND A COMPARISON WITH PREDICTED MODELS

α 1‐Purothionin (α1‐P), a wheatgerm protein and lytic toxin, has a secondary and tertiary structure similar to that of crambin as revealed by CD and NMR studies. α1‐P crystallizes in the tetragonal space group I422 with unit cell dimensions: a = b = 53.59 and c = 69.79 Å. X‐ray diffraction data have been measured to 2.5 Å Bragg spacing. The crystal structure has been determined by molecular replacement methods, using an energy‐minimized α1‐P model structure derived from crambin (Whitlow and Teeter: Journal of Biomolecular Structure and Dynamics 2:831–848, 1985, Journal of the American Chemical Society 108:7163–7172, 1986). The energy‐minimized model gives a slightly cleaner rotation solution and better refinement against the x‐ray data than do the crambin or unminimized α1‐P structures. The final crystallographic residual with the data in the 10–2.5 Å resolution range is 0.216. The refined α1‐P structure has a backbone rms difference of 0.74 Å from crambin and 0.55 Å from the energy‐minimized α1‐P model. A low resolution NMR model of α1‐P calculated from metric matrix distance geometry and restrained molecular dynamics differs from crambin's backbone by 2.3 Å rms deviation (Clore et al.: EMBO Journal 5:2729–2735, 1986). Backbone dihedral angles for our predicted model differ from the refined α1‐P structure in only one region (at a turn where there is a deletion relative to crambin). The NMR model had differences in four regions. Copyright © 1990 Wiley‐Liss, Inc.