Spectroscopic Study of the Interaction between Horse Heart Myoglobin and Zirconium(IV)-Substituted Polyoxometalates as Artificial Proteases.

This study investigated the molecular interactions between horse heart myoglobin and zirconium(IV)-substituted polyoxometalates, and found that, among the studied polyoxometalates, the most efficient at selectively hydrolyzing myoglobin was the 2:2 Zr -Keggin catalyst.

Explanation of Research

• This research dealt with studying the molecular interactions between Horse Heart Myoglobin (HHM) and zirconium(IV)-substituted polyoxometalates (POMs). The main intention of the study was to understand the efficiency of different Zr (IV) substituted POMs in performing selective hydrolysis of HHM, a type of protein.
• The researchers used a range of techniques to understand these molecular interactions. These included circular dichroism (CD), UV/Vis spectroscopy, tryptophan fluorescence spectroscopy, and 1H and 31P NMR spectroscopy. These methods respectively enabled the scientists to study the changes in the protein structure, absorbance and reflectance of the solution, changes in the fluorescence of the tryptophan residues in the protein, and changes in the atomic level properties of hydrogen and phosphorus in the system.

Findings from the Investigation

• A tryptophan fluorescence quenching study was performed to understand the level of interaction between HHM and the examined POMs. This study revealed that 2:2 Zr -Keggin had the strongest interaction with HHM among all the Zr-POMs examined. This makes it the most reactive POM for this system.
• Through 31P NMR spectroscopy studies, it was observed that in solution, 2:2 Zr -Keggin dissociated into a simpler 1:1 Zr -Keggin structure. This simpler structure is speculated to be a catalytically active species, which aids in the hydrolysis of HHM.
• CD, UV/Vis, tryptophan fluorescence, and 1H NMR spectroscopy tests were conducted to understand if HHM undergoes denaturation in the presence of Zr -POMs. The results indicated that the protein does not undergo complete denaturation.
• In addition, CD spectroscopy revealed a decrease in the α-helical content of HHM when Zr -POMs were introduced. This effect was substantially observed in the presence of a large Zr -Wells-Dawson structure, whereas a small Zr -Lindqvist POM showed the least influence.
• The investigation also found that the Soret band at λ=409 nm is maintained in the presence of all examined Zr-POMs. This indicated no significant conformational changes in the protein at the heme group.