3-DIMENSIONAL STRUCTURE OF THE ALKALINE PROTEASE OF PSEUDOMONAS-AERUGINOSA - A 2-DOMAIN PROTEIN WITH A CALCIUM-BINDING PARALLEL-BETA ROLL MOTIF

The three-dimensional structure of the alkaline protease of Pseudomona s aeruginosa, a zinc metalloprotease, has been solved to a resolution of 1.64 angstrom by multiple isomorphous replacement and non-crystallo graphic symmetry averaging between different crystal forms. The molecu le is elongated with overall dimensions of 90 x 35 x 25 angstrom; it h as two distinct structural domains. The N-terminal domain is the prote olytic domain; it has an overall tertiary fold and active site zinc li gation similar to that of astacin, a metalloprotease isolated from a E uropean freshwater crayfish. The C-terminal domain consists of a 21-st rand beta sandwich. Within this domain is a novel 'parallel beta roll' structure in which successive beta strands are wound in a right-hande d spiral, and in which Ca2+ ions are bound within the turns between st rands by a repeated GGXGXD sequence motif, a motif that is found in a diverse group of proteins secreted by Gram-negative bacteria.