Heat-labile enterotoxin crystal forms with variable A/B5 orientation. Analysis of conformational flexibility

Area of Science:

• Structural biology
• Biochemistry
• Microbiology

Background:

• Heat-labile enterotoxin (LT) is a critical virulence factor in bacterial infections.
• Understanding LT's structure-function relationship is key to developing therapeutics.
• Previous studies have characterized various LT crystal forms.

Purpose of the Study:

• To characterize a new native crystal form of heat-labile enterotoxin (LT).
• To investigate the conformational flexibility of the LT A subunit relative to the B pentamer.
• To analyze the impact of A subunit orientation on A-B5 interactions.

Main Methods:

• X-ray crystallography to determine the structure of a new LT crystal form.
• Comparative analysis of multiple LT crystal structures.
• Structural analysis of subunit orientations and interactions.

Main Results:

• A novel native crystal form of LT was identified, containing two AB5 complexes per asymmetric unit.
• Significant conformational freedom was observed in the orientation of the A subunit with respect to the B pentamer across different crystal forms.
• Rotations of the A subunit do not follow a single axis but share a common hinge point near the A-B5 interface.
• High-resolution structural analysis indicates minimal changes in A-B5 interactions despite varied A subunit orientations.

Conclusions:

• The heat-labile enterotoxin (LT) exhibits substantial conformational flexibility in its A subunit orientation.
• This flexibility is achieved through rotation around a conserved hinge region.
• Despite significant rotational freedom, the core interactions between the A and B5 subunits remain largely unchanged.