Cellulose-specific Type B carbohydrate binding modules: understanding oligomeric and non-crystalline substrate...

Area of Science:

• Biochemistry
• Molecular Biology
• Biotechnology

Background:

• Effective enzymatic degradation of crystalline polysaccharides requires synergistic enzyme cocktails tailored to substrate crystallinity.
• Multi-modular enzymes with catalytic and carbohydrate-binding modules (CBMs) facilitate targeted carbohydrate recognition.
• Type B CBMs, particularly families 17 and 28, exhibit unique binding affinities for non-crystalline cellulose over oligomers.

Purpose of the Study:

• To investigate the molecular origins of differential carbohydrate recognition in cellulose-specific Type B CBMs.
• To understand the role of protein-ligand dynamics and binding groove topology in CBM functionality.
• To elucidate the mechanisms by which CBMs recognize non-crystalline cellulose.

Main Methods:

• Molecular dynamics (MD) simulations were employed to analyze protein-ligand dynamics and binding free energies.
• Free energy perturbation with Hamiltonian replica exchange MD was used to test hypotheses on binding groove topology.
• Umbrella sampling MD modeled CBMs with decrystallized cellulose to determine ligand binding free energy.

Main Results:

• Protein-ligand dynamics significantly contribute to variations in oligomer binding affinity within CBM families.
• Binding groove topology influences the necessity for tight oligomer binding, differentiating CBM families.
• Family 17 and 28 CBMs exhibit distinct binding affinities for non-crystalline cellulose and oligomers, aligning with experimental data.

Conclusions:

• Provides unprecedented insight into the substrate recognition mechanisms of Type B CBMs for solid and soluble carbohydrates.
• Findings offer promise for enhancing lignocellulosic biomass conversion technologies.
• Potential applications include the development of novel plant cell wall probes.