Evolution of a transition state: role of Lys100 in the active site of isocitrate dehydrogenase.

ABSTRACT: An active site lysine essential to catalysis in isocitrate dehydrogenase (IDH) is absent from related enzymes. As all family members catalyze the same oxidative ?-decarboxylation at the (2R)-malate core common to their substrates, it seems odd that an amino acid essential to one is not found in all. Ordinarily, hydride transfer to a nicotinamide C4 neutralizes the positive charge at N1 directly. In IDH, the negatively charged C4-carboxylate of isocitrate stabilizes the ground state positive charge on the adjacent nicotinamide N1, opposing hydride transfer. The critical lysine is poised to stabilize-and perhaps even protonate-an oxyanion formed on the nicotinamide 3-carboxamide, thereby enabling the hydride to be transferred while the positive charge at N1 is maintained. IDH might catalyze the same overall reaction as other family members, but dehydrogenation proceeds through a distinct, though related, transition state. Partial activation of lysine mutants by K(+) and NH4 (+) represents a throwback to the primordial state of the first promiscuous substrate family member.

SUBMITTER: Miller SP 

PROVIDER: S-EPMC4389188 | biostudies-literature | 2014 May

REPOSITORIES: biostudies-literature