EPSP synthase

EPSP Synthase

Crystal structure of EPSP synthase.

Introduction

EPSP synthase, or 5-enolpyruvylshikimate-3-phosphate synthase, is an enzyme that plays a crucial role in the shikimate pathway, which is essential for the biosynthesis of aromatic amino acids in plants, bacteria, and fungi. This enzyme catalyzes the reaction between shikimate-3-phosphate (S3P) and phosphoenolpyruvate (PEP) to form 5-enolpyruvylshikimate-3-phosphate (EPSP) and inorganic phosphate.

Structure

EPSP synthase is a monomeric enzyme that typically consists of around 427 amino acids. The enzyme's structure is characterized by a large central domain that binds to the substrate and a smaller domain that undergoes conformational changes during the catalytic cycle. The active site of EPSP synthase is located at the interface of these two domains.

The reaction catalyzed by EPSP synthase.

Mechanism

The catalytic mechanism of EPSP synthase involves the transfer of the enolpyruvyl group from PEP to S3P. This reaction proceeds through a series of steps:

1. Binding of S3P to the enzyme, inducing a conformational change.
2. Binding of PEP to the enzyme-S3P complex.
3. Formation of a tetrahedral intermediate.
4. Release of inorganic phosphate and formation of EPSP.

The enzyme undergoes significant conformational changes during the reaction, which are essential for its catalytic activity.

Inhibition

EPSP synthase is the target of the herbicide glyphosate, which acts as a competitive inhibitor. Glyphosate binds to the active site of the enzyme, preventing the binding of PEP and thus inhibiting the synthesis of EPSP. This inhibition disrupts the shikimate pathway, leading to the depletion of aromatic amino acids and ultimately plant death.

Biological Significance

The shikimate pathway, in which EPSP synthase is a key enzyme, is not present in animals, making it an attractive target for herbicides and antibiotics. The pathway is responsible for the biosynthesis of essential aromatic compounds, including the amino acids phenylalanine, tyrosine, and tryptophan.

Related Pages

• Shikimate pathway
• Glyphosate
• Aromatic amino acids