Involved in the biosynthesis of the macrocyclic amino acid-linked polyketides FK506 and FK520 which are potent immunosuppressants that prevent T-cell proliferation through initial binding to the immunophilin FKBP12. Catalyzes the hydrolysis of chorismate via a 1,4-conjugate elimination of water to yield (4R,5R)-4,5-dihydroxycyclohexa-1,5-dienecarboxylic acid (DCDC). chorismate + H2O = (3R,4R)-3,4-dihydroxy-3,4-dihydrobenzoate + pyruvate Competitively inhibited by 3-(2-carboxyethyl)benzoate. kcat is 17.6 sec(-1) for chorismatase activity with chorismate as substrate. Monomer. Belongs to the FkbO/Hyg5 family.