Chorismate structural studies

Chorismate mutase (CM) catalyzes conversion of chorismate into prephenate in a Claisen rearrangement prephenate is a precursor in the biosynthesis of both i-phenylalanine (i-Phe) and i-tyrosine (i-Ttyr). CM occurs as a dimer for structural studies, the monomer was needed (MacBeath, 1998). The assay for CM activity was based on growth of the colonies in the absence of i-Phe and L-Tyr and thus was based on selection, not screening. One resulting mutant was found to be a monomer and to contain a somewhat polar Ala-Arg-Trp-Pro-Trp-Ala sequence. 

Marti S, J Andres, V Moliner, E Silla, I Tunon, J Bertran (2001) Transition structure selectivity in enzyme catalysis a QM/MM study of chorismate mutase. Theor. Chem. Acc. 105 (3) 207-212... 

Genetic selection is perhaps the most powerful technique currently available for analyzing and directing the evolution of large populations of biomacromolecules. In this chapter, we focus on its use as a tool in studying the structure and function of chorismate mutases. The reader is also referred to other more general reviews [7 - 17]. 

Bruice s contention that there is very little stabilization of the TS by CM, rather it is a favorable binding of the NAC that accounts for its catalytic activity, has been met with much skepticism. An early study by Wiest and Houk" looked at chorismate models with coordinated waters and aminidium cations in positions that matched interacting groups found in the crystal structure of CM with a coordinated substrate. These model computations suggested that the neighboring amino acid residues could be stabilizing the TS. 

COMT is, for many of the same reasons as with chorismate mutase, well suited for the study with computational techniques. The reaction mechanism it catalyzes is the same mechanism that operates in the absence of the enzyme, specifically, the S 2 mechanism, facilitating comparison of the bare solution-phase reaction with the catalyzed reaction. The subsfiate and cofactor do not covalendy bind to the enzyme, so that defining the QM region and the MM region should be relatively uncomplicated. Lasdy, the X-ray crystal structure of COMT bound with the inhibitor 3,5-dinitrocatechol has been determined with a resolution of 2 kP An interesting twist to this enzyme is that the active site includes a metal cation, Mg " ". This crystal structure allows for a natural starting point for computational exploration of the means of the catalytic action of COMT. The rate acceleration provided by COMT is substantial the reaction is 10 times faster within the enzyme than in solution. " ... 

Experimental results for the CM-catalyzed and uncatalyzed reaction, as weU as structural information for chorismate mutase, have been extensively discussed in two previous reviews [2, 3]. There has been a rapid growth of literature in computational studies of chorismate mutase in the last few years. In this chapter, we shall begin by summarizing some key experimental data related to the Claisen rearrangement along with existing structural information for chorismate mutase. We will then review the results of computational studies of chorismate mutase and discuss different proposals that have been suggested for the mechanism of the CM[Pg.1]

The oxabicyclic inhibitor is making a number of other jpearances as well it has starred in two productions already, and its performance in two more is currently being recorded. The X-ray crystal structures of its complexes with the B. subtilis monofunctional chorismate mutase and with the Hilvert catalytic antibody have been reported by William Lipscomb and Yuh-Min Chook at Harvard, and by Ian Wilson and his coworkers at Scripps, respectively, and similar studies with another enzyme and with the Schultz catalytic antibody are underway. When those studies ate completed, we will have an unprecedented oiqx)ttunity to compare the structures of four different proteins that catalyze the same reaction. 

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