Mechanism of Concerted Inhibition of α2β2-type Hetero-oligomeric Aspartate Kinase from Corynebacterium glutamicum*

摘要

Aspartate kinase (AK) is the first and committed enzyme of the biosynthetic pathway producing aspartate family amino acids, lysine, threonine, and methionine. AK from Corynebacterium glutamicum (CgAK), a bacterium used for industrial fermentation of amino acids, including glutamate and lysine, is inhibited by lysine and threonine in a concerted manner. To elucidate the mechanism of this unique regulation in CgAK, we determined the crystal structures in several forms: an inhibitory form complexed with both lysine and threonine, an active form complexed with only threonine, and a feedback inhibition-resistant mutant (S301F) complexed with both lysine and threonine. CgAK has a characteristic α2β2-type heterotetrameric structure made up of two α subunits and two β subunits. Comparison of the crystal structures between inhibitory and active forms revealed that binding inhibitors causes a conformational change to a closed inhibitory form, and the interaction between the catalytic domain in the α subunit and β subunit (regulatory subunit) is a key event for stabilizing the inhibitory form. This study shows not only the first crystal structures of α2β2-type AK but also the mechanism of concerted inhibition in CgAK.