Activity, regulation and molecular dynamics in yeast chorismate mutase

Present only in plants, yeast, fungi, archaebacteria and eubacteria, chorismate mutase isomerizes chorismate to prephrenate in the committed pathway to biosynthesis of Phe and Tyr. The yeast enzyme is allosterically inhibited by Tyr and stimulated by Trp. This isomerization breaks the C5-O (ether) bond, and forms the C1-C9 bond. Development of negative charge on O (ether) is stabilized by Lys 158 and protonated Glu 246, as inferred from the structure of a complex between the enzyme and a transition state inhibitor (TSA). Three aspects of regulation are noted: (i) coordinated changes between helices Hl I and H2, (ii) change in the tilt of H8, and (iii) displacement of H4 and loop L80's away from H8 by Trp. Stocastic boundary molecular simulations of the enzyme-TSA complex to 500 ps were made on five initially constructed complexes: (i) protonated Glu 246 (stable), (ii) deprotonated Glu 246 (unstable), (iii) Glu 246 anion plus H2O between protonated Glu 246 and the ether oxygen (unstable), (iv) the E246Q mutant (stable), and (v) hydroxide anion between protonated Glu 246 and the ether oxygen (unstable). These results, and a Poisson-Bolzmann calculation of the pKa of Glu 246 support its protonation to high pH, consistent with pl-l-rate profiles published earlier.