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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.
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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

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Protein-protein Interfaces

Protein-protein Interfaces

Many proteins form complexes to carry out their functions, making protein-protein interactions (PPIs) essential for an organism's survival. Most PPIs are stabilized by numerous weak noncovalent chemical forces. The physical shape of the interfaces determines the way two proteins interact. Many globular proteins have closely-matching shapes on their surfaces, which form a large number of weak bonds. Additionally, many PPIs occur between two helices or between a surface cleft and a...

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.
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Peptide Bonds

Peptide Bonds

A peptide bond covalently attaches amino acids through a dehydration reaction. One amino acid's carboxyl group and another amino acid's amino group combine, releasing a water molecule. The resulting bond is the peptide bond. The products that such linkages form are peptides. As more amino acids join this growing chain, the resulting chain is a polypeptide. Each polypeptide has a free amino group at one end. This end has the N-terminal, or the amino-terminal, and the other end has a free...

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Related Experiment Video

Updated: Dec 8, 2025

Author Spotlight: A Computational Approach to Decipher Amino Acid Preferences in Multispecific Protein-Protein Interactions

Author Spotlight: A Computational Approach to Decipher Amino Acid Preferences in Multispecific Protein-Protein Interactions

Published on: January 26, 2024

Protein-Peptide Binding Energetics under Crowded Conditions.

Samantha S Stadmiller¹, Jhoan S Aguilar¹, Stuart Parnham²

¹Department of Chemistry, University of North Carolina, Chapel Hill, North Carolina 27599, United States.

The Journal of Physical Chemistry. B

|September 16, 2020

Summary

High concentrations of cellular molecules affect protein interactions. Researchers used 19F NMR to study how proteins, sugars, and urea impact SH3-SOS peptide binding, finding protein cosolutes are crucial for understanding cell signaling.

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Area of Science:

Biophysics
Cellular Biology
Biochemistry

Background:

Biological processes occur in crowded cellular environments with high macromolecule concentrations (>300 g/L).
Protein-protein interactions, like SH3 domain with Son of Sevenless (SOS) peptide, are vital for cell signaling but often studied in dilute solutions.
Understanding these interactions under physiological crowding is essential for cell biology.

Purpose of the Study:

To investigate the impact of high concentrations of protein, sugar, and urea cosolutes on the kinetics and thermodynamics of SH3-peptide binding.
To analyze the temperature dependence of binding to quantify enthalpic and entropic contributions.
To assess the influence of cosolutes on SH3 diffusion and relate it to binding kinetics.

Main Methods:

Utilized 19F NMR lineshape analysis to study SH3-peptide binding kinetics and thermodynamics.
Performed temperature-dependent measurements to determine binding energetics.
Quantified translational and rotational diffusion of SH3 in various cosolute conditions.

Main Results:

Protein cosolutes exhibited different binding energetics compared to small molecule cosolutes (sugars, urea).
Most protein cosolutes destabilized SH3-peptide complexes, with non-generalizable effects suggesting specific weak interactions.
Cosolute effects on SH3 diffusion did not always correlate with kinetic changes, indicating peptide properties are also important.

Conclusions:

Physiologically relevant protein cosolutes are critical for accurate studies of macromolecular crowding effects on protein interactions.
The energetic effects of crowding are complex and depend on both the protein and the crowded environment.
Considering the behavior of all interacting partners, including intrinsically disordered peptides, is necessary for interpreting crowding effects in cellular contexts.