Structural and functional characterization of a novel type-III dockerin from Ruminococcus flavefaciens

Area of Science:

• Microbiology
• Biochemistry
• Structural Biology

Background:

• Ruminococcus flavefaciens possesses complex cellulosomes for plant biomass degradation.
• Scaffoldin proteins, crucial for cellulosome assembly, contain dockerin modules that bind cohesins.
• A novel type-III dockerin subtype was recently identified in Ruminococcus flavefaciens scaffoldins.

Purpose of the Study:

• To investigate the calcium (Ca²⁺)-binding properties of the type-III dockerin from the ScaA scaffoldin (ScaADoc).
• To characterize the structural and biophysical behavior of ScaADoc in response to Ca²⁺.
• To assess the potential of ScaADoc for applications in designer cellulosome construction.

Main Methods:

• Phylogenetic analysis to identify novel dockerin subtypes.
• Circular dichroism (CD) spectroscopy to assess protein structure changes.
• Isothermal titration calorimetry (ITC) to quantify binding affinities.
• Differential scanning calorimetry (DSC) for thermal stability analysis.
• Nuclear magnetic resonance (NMR) spectroscopy for structural insights.

Main Results:

• ScaADoc, a type-III dockerin, exhibits significant Ca²⁺-responsiveness despite lacking a second canonical Ca²⁺-binding loop.
• Biophysical analyses demonstrated Ca²⁺-dependent structural changes and binding interactions.
• ScaADoc displayed comparable Ca²⁺-binding affinity to the cohesin from ScaB scaffoldin, similar to other known dockerins.
• The study confirmed the robustness of dockerin modules in binding interactions.

Conclusions:

• The type-III dockerin (ScaADoc) possesses functional Ca²⁺-binding capabilities.
• Dockerin modules demonstrate inherent robustness and adaptability in their Ca²⁺-dependent interactions.
• The Ca²⁺-binding properties of ScaADoc can be leveraged for the engineering of novel designer cellulosomes for biotechnological applications.