Crystallization and rhenium MAD phasing of the acyl-homoserinelactone synthase EsaI

Acyl-homoserine-L-lactones (AHLs) are diffusible chemical signals that are required for virulence of many Gram-negative bacteria. AHLs are produced by AHL synthases from two substrates, S-­adenosyl-L-methionine and acyl-acyl carrier protein. The AHL synthase EsaI, which is homologous to the AHL synthases from other pathogenic bacterial species, has been crystallized in the primitive tetragonal space group P4₃, with unit-cell parameters a = b = 66.40, c = 47.33 Å. The structure was solved by multiple-wavelength anomalous diffraction with a novel use of the rhenium anomalous signal. The rhenium-containing structure has been refined to a resolution of 2.5 Å and the perrhenate ion binding sites and liganding residues have been identified.