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The Equilibrium Binding Constant and Binding Strength

The Equilibrium Binding Constant and Binding Strength

The equilibrium binding constant (Kb) quantifies the strength of a protein-ligand interaction. Kb can be calculated as follows when the reaction is at equilibrium:

The Equilibrium Binding Constant and Binding Strength

The Equilibrium Binding Constant and Binding Strength

The equilibrium binding constant (Kb) quantifies the strength of a protein-ligand interaction. Kb can be calculated as follows when the reaction is at equilibrium:

Ligand Binding Sites

Ligand Binding Sites

Proteins are dynamic macromolecules that carry out a wide variety of essential processes; however, the activities of most proteins depend on their interactions with other molecules or ions, known as ligands.
Protein-ligand interactions are quite specific; even though numerous potential ligands surround a cellular protein at any given time, only a particular ligand can bind to that protein. Moreover, a ligand binds only to a dedicated area on the surface of the protein, known as the...

Ligand Binding Sites

Ligand Binding Sites

Proteins are dynamic macromolecules that carry out a wide variety of essential processes; however, the activities of most proteins depend on their interactions with other molecules or ions, known as ligands.
Protein-ligand interactions are quite specific; even though numerous potential ligands surround a cellular protein at any given time, only a particular ligand can bind to that protein. Moreover, a ligand binds only to a dedicated area on the surface of the protein, known as the...

Conserved Binding Sites

Conserved Binding Sites

Many proteins’ biological role depends on their interactions with their ligands, small molecules that bind to specific locations on the protein known as ligand-binding sites. Ligand-binding sites are often conserved among homologous proteins as these sites are critical for protein function.
Binding sites are often located in large pockets, and if their location on a protein’s surface is unknown, it can be predicted using various approaches. The energetic method computationally analyses the...

Conserved Binding Sites

Conserved Binding Sites

Many proteins’ biological role depends on their interactions with their ligands, small molecules that bind to specific locations on the protein known as ligand-binding sites. Ligand-binding sites are often conserved among homologous proteins as these sites are critical for protein function.
Binding sites are often located in large pockets, and if their location on a protein’s surface is unknown, it can be predicted using various approaches. The energetic method computationally analyses the...

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Related Experiment Video

Updated: Jun 17, 2026

Fluorescence Anisotropy as a Tool to Study Protein-protein Interactions

Fluorescence Anisotropy as a Tool to Study Protein-protein Interactions

Published on: October 21, 2016

How much binding affinity can be gained by filling a cavity?

Yuko Kawasaki¹, Eduardo E Chufan, Virginie Lafont

¹Department of Biology, Johns Hopkins University, Baltimore, MD 21218, USA.

Chemical Biology & Drug Design

|December 24, 2009

Summary

Optimizing drug binding affinity involves filling cavities with functionalities that enhance geometric fit. This study reveals three thermodynamic phases, leading to significant binding affinity increases and providing lead optimization guidelines.

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Determining Binding Affinity (KD) of Radiolabeled Antibodies to Immobilized Antigens

Determining Binding Affinity (K_D) of Radiolabeled Antibodies to Immobilized Antigens

Published on: June 23, 2022

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Last Updated: Jun 17, 2026

Fluorescence Anisotropy as a Tool to Study Protein-protein Interactions

Fluorescence Anisotropy as a Tool to Study Protein-protein Interactions

Published on: October 21, 2016

Determining Binding Affinity (KD) of Radiolabeled Antibodies to Immobilized Antigens

Determining Binding Affinity (K_D) of Radiolabeled Antibodies to Immobilized Antigens

Published on: June 23, 2022

Area of Science:

Medicinal Chemistry
Biophysics
Computational Chemistry

Background:

Drug development relies heavily on optimizing binding affinity.
Geometric fit and specific interactions are key to drug efficacy.
Understanding thermodynamic contributions is crucial for rational drug design.

Purpose of the Study:

To evaluate the thermodynamic consequences of van der Waals interactions in drug binding.
To investigate the impact of increasing van der Waals radii on binding affinity.
To identify thermodynamic signatures guiding lead optimization.

Main Methods:

Systematic evaluation of functionalities with increasing van der Waals radii (-H, -F, -Cl, CH(3)).
Analysis of thermodynamic parameters: enthalpy and entropy changes.
Correlation of thermodynamic signatures with binding affinity changes.

Main Results:

A two-orders-of-magnitude increase in binding affinity was observed.
Three distinct thermodynamic phases were identified.
Phase 1: Enthalpy gain (-1.5 kcal/mol) and entropy loss (+0.9 kcal/mol) yielding a 3.5-fold affinity increase.
Phase 2: Simultaneous enthalpic and entropic gains, improving affinity 25-fold.
Phase 3: Trend collapse with functionalities larger than the cavity, causing significant enthalpy and affinity losses.

Conclusions:

Van der Waals interactions play a critical role in modulating binding affinity.
Distinct thermodynamic phases offer insights into binding mechanisms.
The observed thermodynamic signatures provide valuable guidelines for lead optimization in drug discovery.