Subunit Communication in the Anthranilate Synthase Complex from Salmonella typhimurium

The anthranilate synthase-phosphoribosyl transferase complex of the tryptophan biosynthetic pathway in Salmonella typhimurium is an allosteric, heterotetrameric (TrpE2-TrpD2) enzyme whose multiple activities are negatively feedback-regulated by L-tryptophan. A hybrid complex containing one catalytically active, feedback-insensitive and one catalytically inactive, feedback-sensitive mutant TrpE subunit was assembled in vitro and used to investigate communication between regulatory and catalytic sites located on different subunits. The properties of the hybrid complex demonstrate that the binding of a single inhibitor molecule to one TrpE subunit is sufficient for the propagation of a conformational change that affects the active site of the companion subunit.