Electrochemical and Spectroscopic Characterization of Co-Neuroglobin: A Bioelectrocatalyst for H₂ Production

Area of Science:

• Biophysical Chemistry
• Bioinorganic Chemistry
• Protein Engineering

Background:

• Human neuroglobin (Hgb) is an oxygen-binding protein involved in oxygen transport and storage.
• Cobalt (Co) substitution in heme proteins can alter their electronic and catalytic properties.
• Understanding the role of specific amino acid residues, like Cys46 and Cys55, is crucial for protein function.

Purpose of the Study:

• To investigate the electronic and spectroscopic properties of cobalt-substituted wild-type (Co-WT) and C46A/C55A mutant human neuroglobin (Co-C46AC55A) in both Co(III) and Co(II) oxidation states.
• To compare these properties with iron (Fe) counterparts and other Co-heme proteins.
• To evaluate the electrocatalytic activity of these Co-neuroglobin variants for hydrogen production.

Main Methods:

• Electronic absorption, Magnetic Circular Dichroism (MCD), and Resonance Raman (RR) spectroscopy.
• Electrochemical measurements to determine redox potentials and catalytic activity.
• Comparison with existing data for Fe-neuroglobin and other Co-heme proteins.

Main Results:

• Both Co-WT and Co-C46AC55A contain low-spin, six-coordinated cobalt ions, with electronic properties largely unaffected by the C46-C55 disulfide bond deletion.
• The redox potentials (E°') for Co(III)/Co(II) are negative and pH-dependent, similar to Fe-neuroglobin.
• Co-WT and Co-C46AC55A exhibit significant electrocatalytic activity for H+ reduction to H2, comparable to Co-porphyrin catalysts, with reduced sensitivity to dioxygen.

Conclusions:

• Cobalt substitution in human neuroglobin yields stable, catalytically active species for hydrogen evolution.
• The C46-C55 disulfide bond does not significantly influence the electronic structure or catalytic function of Co-neuroglobin.
• These findings highlight the potential of engineered heme proteins as electrocatalysts.