Until now, phospholipase A 2 (PLA 2 ; EC 3.1.14) has been found only from eukaryotic sources. In the present study, we found a secreted PLA 2 , which is produced by a soil bacterium, Streptomyces violaceoruber A-2688, demonstrating that the enzyme is the first phospholipase A 2 identified in prokaryote. After characterization of the novel PLA 2 , a gene encoding the enzyme was cloned, sequenced, and overexpressed using a Streptomyces host-vector system. The amino acid sequence showed that the prokaryotic PLA 2 has only four cysteines and less homology to the eukaryotic ones, which have 12-16 cysteines. The solution structures of the prokaryotic PLA 2 , bound and unbound with calcium(II) ion, were determined by using the NMR technique and structure calculation. The overall structure of the S. violaceoruber PLA 2 , which is composed of only five ␣-helices, is completely different from those of eukaryotic PLA 2 s, which consist of ␤-sheets and ␣-helices. The structure of the calcium-binding domain is obviously distinct from that without the ion; the ligands for the calcium(II) ion are the two carboxylates of Asp 43 (monodentate) and Asp 65(bidentate), the carbonyl oxygen of Leu 44 , and three water molecules. A calcium-binding experiment showed that the calcium dissociation constant (ϳ5 mM) for the prokaryotic PLA 2 is much larger than those of eukaryotic ones.

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