Omptins are a family of enterobacterial surface proteases/adhesins that share high sequence identity and a conserved ß-barrel fold in the outer membrane. The omptins are multifunctional, and the individual omptins exhibit differing virulence-associated functions.This family contains a number of integral outer membrane serine proteases that differ from trypsin-like proteases in that they cleave polypeptides between two basically charged amino acids. Escherichia coli OmpT protein has previously been classified as a serine protease with Ser(99) and His(212) as active site residues. The X-ray structure of the Enzyme is inconsistent with this classification, and the involvement of a nucleophilic water molecule, activated by the residue pair Asp(210)/His(212), classifies the enzyme as an aspartic endopeptidase with the activity also strongly dependent on Asp(83) and Asp(85). Both may function in binding of the water molecule and/or in oxyanion stabilization. The transmembrane ß-barrel, consists of 10 ß-strands, and the enzymatic activity depends on reversible dimerization.

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