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Does Ionic Screening Lower Activation Barriers for Conformational Transitions in Proteins?

Jan M Antosiewicz¹, Maciej Długosz¹

¹Division of Biophysics, Institute of Experimental Physics, Faculty of Physics , University of Warsaw , Pasteura 5 , 02-105 Warsaw , Poland.

The Journal of Physical Chemistry. B

|November 28, 2018

Summary

This summary is machine-generated.

This study reveals protein-carbohydrate binding kinetics, showing ionic strength influences conformational changes. Increased ionic strength accelerates both forward and reverse conformational transitions in hen egg-white lysozyme binding with tri-N-acetylglucosamine.

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Area of Science:

Biochemistry
Chemical Kinetics
Protein-Ligand Interactions

Background:

Hen egg-white lysozyme (HEWL) is a model protein for studying enzyme kinetics.
Understanding protein-ligand binding mechanisms is crucial in biochemistry.
Tri-N-acetylglucosamine is a key substrate analogue for lysozyme.

Purpose of the Study:

To investigate the binding kinetics of HEWL with tri-N-acetylglucosamine.
To determine the influence of pH and ionic strength on the binding mechanism.
To elucidate the elementary stages and rate constants governing the binding process.

Main Methods:

Stopped-flow spectroscopy utilizing tryptophyl fluorescence.
Kinetic analysis through numerical integration of chemical master equations.
Systematic variation of solution pH (3.2 and 11) and ionic strength.

Main Results:

The binding process follows a two-step mechanism involving four elementary stages.
Rate constants for conformational transitions (forward and reverse) were evaluated.
Both forward and reverse conformational transition rate constants increase with ionic strength, irrespective of pH.

Conclusions:

The binding mechanism involves diffusional complex formation, dissociation, and conformational transitions.
Ionic strength modulates protein conformational dynamics during binding.
Ionic screening of electrostatic interactions likely lowers the activation barrier for protein conformational changes.