Structure-function analyses generate novel specificities to assemble the components of multienzyme bacterial...

Area of Science:

• Biochemistry
• Molecular Biology
• Structural Biology

Background:

• Cellulosomes are complex bacterial nanomachines essential for degrading plant biomass.
• Assembly relies on specific interactions between dockerin and cohesin modules.
• Acetivibrio cellulolyticus utilizes a unique scaffoldin system (ScaA, ScaB, ScaC) for cellulosome organization.

Purpose of the Study:

• To elucidate the mechanism underlying the specificity of type-I cohesin-dockerin interactions in Acetivibrio cellulolyticus.
• To investigate the roles of ligand-binding surfaces and structural scaffolds in mediating these specificities.
• To engineer novel specificities within the cellulosome assembly machinery.

Main Methods:

• Crystal structure determination of an enzyme dockerin bound to a ScaA cohesin.
• Site-directed mutagenesis to identify specificity-determining amino acid residues.
• Rational design and protein engineering to alter cohesin-dockerin binding specificities.

Main Results:

• The crystal structure revealed two identical binding orientations for enzyme dockerins on ScaA cohesins.
• Mutagenesis identified residues crucial for type-I cohesin-dockerin specificity in A. cellulolyticus.
• Novel specificities were successfully engineered into ScaB-associated dockerins, but not enzyme-associated dockerins.

Conclusions:

• Dockerin specificity is determined by an intricate interplay between the ligand-binding surface and the structural scaffold.
• The findings provide insights into the modular assembly of complex enzymatic systems.
• This study offers a foundation for engineering tailored cellulosomes for biomass degradation.