Sandbox Reserved 1068: Difference between revisions

Isochorismate is converted to salicylate and pyruvate through abstraction of the C2 hydrogen followed by protonation of C9 atom and the breakage of the C3-O7 bond. Histidine residue (His334) was proposed to act as a base, abstracting the C2 proton of isochorismate through a second order elimination mechanism. However, recent studies have shown that this residue lies more than '''13 A''' away from C2 atom and no other water molecules appear close enough to the C2 atom to act as a base. IPL reaction has been proposed to proceed through an intramolecular pericyclic mechanisms, involving a concerted hydrogen transfer from C2 to C9 and breakage of the C3-O7 bond.  

A magnesium ion in the active site orients the C1 carboxyl group of chorismate. A lysine residue then serves as a general base for the activation of a water molecule to attack at C2. The catalytic mechanism for conversion of isochorismate to salicylate by MbtI is a sigmatropic, pericyclic mechanism that is pH-dependent. Chromate mutase activity is only observed in the absence of magnesium ion in the active site while salicylate synthase activity is depended on magnesium ion. The active site of MbtI is altered by the removal of the magnesium cofactor causing chromate mutase activity. MbtI has differing binding modes for chromate that leads to different substrate conformations/transition states and resulting in different products.