Probing lectin-mucin interactions by isothermal titration microcalorimetry

Area of Science:

• Biochemistry
• Biophysics
• Molecular Biology

Background:

• Isothermal titration microcalorimetry (ITC) is a powerful tool for determining thermodynamic binding parameters of biological molecules.
• While extensively used for lectin-carbohydrate interactions, its application to lectin-glycoprotein binding is less explored.
• Challenges like sample precipitation and high sample requirements can hinder ITC experiments.

Purpose of the Study:

• To investigate the thermodynamic binding parameters of lectin-glycoprotein interactions using ITC.
• To explore the binding mechanism of lectins with multivalent glycoproteins like mucins.
• To understand the entropic contributions to high-affinity lectin-mucin interactions.

Main Methods:

• Utilized Isothermal Titration Microcalorimetry (ITC) to measure binding thermodynamics.
• Studied the interactions between lectins and various forms of mucins (multivalent globular and linear glycoproteins).
• Employed careful experimental design to overcome common ITC challenges such as sample precipitation.

Main Results:

• Determined thermodynamic binding parameters (affinity, stoichiometry, enthalpy, entropy, free energy) for lectin-mucin interactions.
• Observed a dynamic binding mechanism involving lectins binding and 'jumping' between carbohydrate epitopes on mucins, leading to increased affinity.
• Found that high-affinity lectin-mucin cross-linking is primarily driven by favorable binding entropy associated with the 'bind and jump' mechanism.

Conclusions:

• The 'bind and jump' mechanism enhances lectin affinity for multivalent glycoproteins like mucins.
• Lectin-mucin binding shares mechanistic similarities with protein-DNA interactions.
• Enhanced entropic effects may represent a common binding mechanism for ligands interacting with biopolymers in general.