Catalyzes the cyclization of 2-amino-4,5-dihydroxy-6-one-heptanoic acid-7-phosphate to yield 3-amino-4-hydroxybenzoic acid (3,4-AHBA). 2-amino-4,5-dihydroxy-6-oxo-7-(phosphooxy)heptanoate = 3-amino-4-hydroxybenzoate + H(+) + 2 H2O + phosphate Manganese. Cobalt, iron and magnesium can be used to a lesser extent. Partially inhibited by 0.1 mM pyridoxal phosphate. This Km value might be underestimated because the concentration of the substrate determined is perhaps lower than the actual concentration due to the instability of the substrate compound. Optimum pH is 6.5-10.5. Optimum temperature is 30 degrees Celsius. Monomer. Belongs to the archaeal-type DHQ synthase family. GriH subfamily.