Integrative structure determination reveals functional global flexibility for an ultra-multimodular arabinanase

Area of Science:

• Biochemistry
• Structural Biology
• Enzymology

Background:

• AbnA is a bacterial enzyme from Geobacillus stearothermophilus.
• It belongs to the GH43 family and degrades arabinan.

Purpose of the Study:

• To determine the full-length crystal structure of AbnA.
• To investigate its ultra-multimodular architecture and novel domains.
• To characterize its conformational flexibility and functional movements.

Main Methods:

• X-ray crystallography
• Integrative structure determination (molecular dynamics, metadynamics, normal mode analysis, SAXS, DLS, cross-linking, kinetics)

Main Results:

• The crystal structure of AbnA revealed an unprecedented ultra-multimodular architecture within GH43 family.
• Two novel, uncharacterized carbohydrate-binding module (CBM) families were identified within AbnA.
• Three crystallographic conformational states were determined, showing large functional conformational changes (~100 Å domain movement).

Conclusions:

• AbnA possesses a unique, large, and flexible ultra-multimodular structure.
• The identified novel CBMs suggest new arabinan-binding mechanisms.
• The integrative structure determination approach is effective for studying large conformational changes in multimodular proteins.