Allosterically switchable network orients β-flap in Clostridioides difficile toxins.

Area of Science:

• Biochemistry
• Molecular Biology
• Structural Biology

Background:

• Allosteric proteins respond to ligand binding distant from the active site.
• Clostridioides difficile toxins utilize myo-inositol hexakisphosphate for autoproteolysis within host cells.
• Ligand binding induces conformational changes, notably in the beta-flap region, leading to two distinct orientations.

Purpose of the Study:

• To elucidate the mechanism of allosteric transition in Clostridioides difficile toxins.
• To identify key interactions driving the conformational shift upon cofactor binding.
• To explore the potential for therapeutic targeting of toxin autoproteolysis.

Main Methods:

• Extensive atomistic molecular dynamics simulations.
• Computational and experimental mutagenesis.
• Analysis of switchable interaction networks.

Main Results:

• A mechanism for allosteric transition involving a switchable interaction network was uncovered.
• The K600-E743 interaction pair is identified as the most significant contributor, accounting for ~70% of the allosteric effect.
• The interaction network adopts two mutually exclusive configurations, rather than a gradual transition, for active and inactive states.

Conclusions:

• The allosteric mechanism in C. difficile toxins relies on a discrete switchable interaction network.
• This mechanism, characterized by distinct configurations, offers a new perspective on allostery.
• Understanding this process can inform the development of drugs targeting C. difficile toxin autoproteolysis.