Escherichia coli aspartate transcarbamylase: the relation between structure and function

Area of Science:

• Biochemistry
• Structural Biology
• Enzymology

Background:

• Aspartate transcarbamylase (ATCase) is a key enzyme in pyrimidine biosynthesis.
• Allosteric enzymes regulate metabolic pathways through conformational changes.
• Understanding ATCase structure is crucial for deciphering enzyme regulation.

Purpose of the Study:

• To determine the X-ray structures of aspartate transcarbamylase in its T and R allosteric forms.
• To elucidate the structural basis for allosteric regulation and enzyme function.
• To provide a foundation for understanding metabolic pathway control by enzymes.

Main Methods:

• X-ray crystallography was used to solve and refine the structures of ATCase.
• The T form was studied with cytidine triphosphate (CTP), an inhibitor.
• The R form was studied with N-phosphonacetyl-L-aspartate, a bisubstrate analog.

Main Results:

• High-resolution X-ray structures were obtained for both the T and R states of ATCase.
• Structural differences between the T and R states highlight conformational changes upon ligand binding.
• Site-directed mutagenesis identified key residues involved in catalysis and cooperativity.

Conclusions:

• The determined structures offer critical insights into the allosteric mechanisms of ATCase.
• This work advances the understanding of how enzymes control metabolic flux.
• The findings pave the way for further investigations into enzyme function and regulation.