Members of the Outer membrane phospholipase A (OMPLA) family are integral membrane phospholipases, present in many Gram-negative bacteria with a broad substrate specificity. The role of OMPLA has been most thoroughly studied in Escherichia coli, where it participates in the secretion of colicins. The three-dimensional structure of OmplA of Escherichia coli has been determined, revealing a 12-stranded antiparallel ß-barrel with a convex and a flat side. The active site residues are exposed at the exterior of the flat face of the barrel. The activity of the enzyme is calcium-dependent and regulated by reversible dimerisation. Dimer interactions occur exclusively in the membrane-embedded parts of the flat side of the barrel, with polar residues embedded in an apolar environment forming the key interactions. The active site (Asn-156-His-142-Ser-144) is located at the exterior of the barrel, at the outer leaflet side of the membrane. The phospholipids of the inner leaflet are believed to be presented to the active site of OMPLA by perturbation of the membrane causing the formation of non-bilayer structures and finally leading to the formation of the active dimer.

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