The crystal structure of the serratia protease from Serratia sp. E15, a zinc metalloprotease, has been solved at a 2.0Å resolution by a multiple isomorphous replacement with the anomalous dispersion of Zn contained in itself. It consists of two domains. The N-terminal domain is the proteolytic domain. Within the C-terminal domain, there is found novel ‘β-sheet coil’ structure in which successive β-strands wound into right-handed coil. The β-sheet coil is formed by repeated XLXGGXGXD amino acid sequence motifs and Ca+2 ions bound between a pair of it's loops.