In Gram-negative bacteria, intercellular communication and virulence regulation is mediated by the diffusible chemical signal acyl-homoserine-L-lactone (AHL). The AHL synthase enzymes produce a variety of AHLs from the substrates S-adenosyl-L-methionine and acyl-acyl carrier protein. LasI, the AHL synthase from Pseudomonas aeruginosa, has low solubility and has failed to crystallize despite extensive crystallization trials. Based on the previously determined structure of the AHL synthase EsaI, active soluble LasI was produced by re-engineering residues in a tight turn to produce a type I' beta-turn. The resulting protein is active, more stable than the wild-type LasI and has been crystallized in the cubic space group F23, with unit-cell parameters a = b = c = 154.90 A.