Control and recognition of anionic ligands in myoglobin

Area of Science:

• Biochemistry
• Molecular Biology
• Protein Engineering

Background:

• Myoglobin (Mb) is a crucial protein for oxygen transport and storage.
• The distal histidine (His E7) plays a key role in modulating Mb's ligand-binding properties.
• Understanding Mb structure-function relationships informs protein engineering and drug design.

Purpose of the Study:

• To investigate the impact of specific mutations on myoglobin's ligand-binding kinetics and equilibrium.
• To explore alternative mechanisms of ligand stabilization in myoglobin variants lacking the distal histidine.
• To compare the stability of ligand adducts in engineered myoglobins with wild-type sperm whale, horse, and Aplysia limacina myoglobins.

Main Methods:

• Site-directed mutagenesis of a synthetic sperm whale myoglobin gene.
• Equilibrium and kinetic experiments to measure ligand binding.
• Analysis of ferric and ferrous myoglobin mutants and wild-type proteins.

Main Results:

• Mutants with an arginyl residue at position E10 (His E7 Val-Thr E10 Arg) exhibited greatly enhanced stability of Mb:heme ligand adducts.
• Comparison with wild-type sperm whale, horse, and Aplysia limacina myoglobins highlighted the stabilizing effect of the E10 arginyl residue.
• Reactivity differences between ferric and ferrous states of wild-type and mutant myoglobins were characterized.

Conclusions:

• The introduction of an arginyl residue at position E10 significantly stabilizes myoglobin-ligand complexes.
• Myoglobins lacking the distal histidine may employ alternative mechanisms for ligand stabilization.
• These findings provide insights into protein structure-function relationships and potential for protein engineering.