REVIEW Crystal Structure of Alkaline Protease from

The three-dimensional structure of alkaline protease from Pseudomonas eruginosa IF03455, a zinc-requiring metalloprotease, has been determined by a multiple isomorphous replacement method of X-ray crystallography, and refined at 2.3 A resolution to the R-factor of 0.198. The molecule has an elongated ellipsoidal shape with approximate dimensions of 90 X 42 X 35 A. It consists of two distinct structural domains. The N-terminal domain is the proteolytic domain which contains the active site zinc atom in the inside of the large cleft. The overall structure of the domain is similar to that of astacin, a metalloprotease belonging to a superfamily different from that of the alkaline protease. The C-terminal domain has a two-layer /3-sandwich structure consisting of 19 /3-strands. In the central region of this domain is an unusual parallel /3-helix structure in which successive /3-strands are wound in a right-handed spiral through the short turns between the strands. Ca2+ ions bound internally within the turns formed by a repeated GGXGXD sequence motif may play an essential role in stabilizing this /3-helix structure. KEY WORDS: Alkaline protease / X-ray analysis / /-helix / Pseudomonas aeruginosa