CRYSTAL STRUCTURES OF WILD-TYPE P-HYDROXYBENZOATE HYDROXYLASE COMPLEXED WITH 4-AMINOBENZOATE, 2,4-DIHYDROXYBENZOATE AND 2-HYDROXY-4-AMINOBENZOATE AND OF THE TRY222ALA MUTANT, COMPLEXED WITH 2-HYDROXY-4-AMINOBENZOATE. EVIDENCE FOR A PROTON CHANNEL AND A NEW BINDING MODE OF THE FLAVIN RING
