The alkaline proteinase from the mesophilic bacterium Bacillus mesentericus has
been crystallized in a 1:1 complex with the inhibitor eglin-C from the medical
leech. The crystals have cell dimensions of a = 43.0, b = 71.9, c = 48.3 A and
beta = 110.0 degrees and are in the space group P2(1). Three-dimensional data to
2.0 A have been recorded on film from a single crystal. The orientation and
position of the complex in the unit cell have been established using the refined
coordinates of subtilisin Carlsberg and of eglin-C as independent models. The
structure of the complex has been refined by restrained least-squares
minimization. The crystallographic R factor (= sigma[magnitude of Fo - magnitude
of Fc[/sigma magnitude of Fo) is 15.1% including two Ca2+ ions and 312 water
molecules. The structure is discussed in terms of its physicochemical properties
in solution and its relation to other Bacillus subtilisins.
