Conformational changes in ammonia-channeling glutamine amidotransferases

Area of Science:

• Biochemistry
• Structural Biology
• Enzymology

Background:

• Glutamine amidotransferases (GATs) are enzymes that synthesize aminated products.
• These enzymes channel ammonia from a glutamine substrate to an acceptor substrate over distances of 10-40 Å.
• Ammonia production typically involves a cysteine-histidine-glutamate triad or an N-terminal cysteine residue.

Purpose of the Study:

• To elucidate the structural mechanisms underlying ammonia channeling in GATs.
• To understand the conformational changes involved in enzyme activation and substrate binding.

Main Methods:

• Determination of crystal structures of amidotransferase-ligand complexes.
• Analysis of structural data to visualize catalytic intermediates and domain movements.

Main Results:

• Crystal structures reveal enzyme-ligand complexes mimicking catalytic cycle intermediates.
• Acceptor binding was observed to activate the glutaminase site via domain-hinged movements and conformational changes.
• Flexible loops in synthase and glutaminase domains were shown to shield catalytic sites, anchor substrates, and regulate the ammonia channel.

Conclusions:

• Structural insights provide a detailed view of GAT catalytic mechanisms.
• Enzyme conformational flexibility plays a critical role in substrate binding, activation, and ammonia channeling.
• Understanding these mechanisms can inform the design of novel enzyme inhibitors or activators.