Ligand Binding Rate Constants in Heme Proteins Using Markov State Models and Molecular Dynamics Simulations

Area of Science:

• Biochemistry
• Computational Biology
• Structural Biology

Background:

• Ligand migration is crucial for protein function, especially in heme proteins where it precedes heme iron binding.
• Understanding ligand migration pathways in globins provides insights into their diverse biological roles.

Purpose of the Study:

• To investigate the molecular mechanisms of O2 and NO migration in two truncated hemoglobins from Mycobacterium tuberculosis (Mt-TrHbN and Mt-TrHbO).
• To elucidate the factors influencing ligand association constants in different hemoglobin states.

Main Methods:

• Utilized molecular dynamics simulations to model ligand movement.
• Employed a Markov State Model to analyze migration pathways.
• Applied empirical kinetic equations to quantify migration processes.

Main Results:

• Identified key events in ligand migration, including site transitions and gate dynamics.
• Demonstrated that differences in association constants for Mt-TrHbN are primarily due to water molecule displacement in the deoxy state.
• Characterized distinct migration behaviors for O2 and NO.

Conclusions:

• The combined approach of simulations, Markov State Models, and kinetic equations offers a powerful framework for studying ligand migration in globins.
• Displacement of water molecules is a critical factor modulating ligand binding affinity in truncated hemoglobins.