Structure and function of a complex between chorismate mutase and DAHP synthase: efficiency boost for the junior...

Area of Science:

• Biochemistry
• Structural Biology
• Microbial Metabolism

Background:

• Chorismate mutase is crucial for the shikimate pathway, producing phenylalanine and tyrosine.
• Mycobacterium tuberculosis chorismate mutase (MtCM) exhibits low intrinsic catalytic activity.
• MtCM's poor activity is linked to a lack of prominent active-site residues.

Purpose of the Study:

• To investigate the structural basis for the activation of MtCM by DAHP synthase (MtDS).
• To elucidate the mechanism of catalytic enhancement and regulation of the shikimate pathway in M. tuberculosis.
• To explore the prevalence of similar enzyme complexes in Actinomycetales.

Main Methods:

• X-ray crystallography of the MtCM-MtDS complex bound to a transition-state analogue.
• Site-directed mutagenesis of MtCM, focusing on its C-terminal extrusion.
• Enzyme activity assays and synergistic inhibition studies with phenylalanine and tyrosine.

Main Results:

• A 2.35 Å crystal structure revealed a complex with MtDS forming a central core and MtCM dimers on the periphery.
• Binding to MtDS repositions MtCM active-site residues, leading to >100-fold catalytic efficiency increase.
• Mutagenesis confirmed conserved residues in MtCM's C-terminal extrusion are vital for activation.
• The MtCM-MtDS complex exhibited synergistic inhibition by phenylalanine and tyrosine, unlike MtCM alone.

Conclusions:

• Complex formation between MtCM and MtDS activates MtCM's chorismate mutase activity.
• This interaction provides a critical regulatory mechanism for the M. tuberculosis shikimate pathway.
• Non-covalent complexes of AroQ(delta) subclass chorismate mutases with synthase partners are common in Actinomycetales.