Helicobacter pylori AmiF formamidase that hydrolyzes formamide to produce formic acid and ammonia belongs to a member of the nitrilase superfamily. The crystal structure of AmiF was solved to 1.75 Å resolution using single-wavelength anomalous dispersion methods. The structure consists of a homohexamer related by 3-fold symmetry in which each subunit has an ␣-␤-␤-␣ four-layer architecture characteristic of the nitrilase superfamily. One exterior ␣ layer faces the solvent, whereas the other one associates with that of the neighbor subunit, forming a tight ␣-␤-␤-␣-␣-␤-␤-␣ dimer. The apo and liganded crystal structures of an inactive mutant C166S were also determined to 2.50 and 2.30 Å , respectively. These structures reveal a small formamide-binding pocket that includes

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