Structural insights into the interaction between molluscan hemocyanins and phenolic substrates: An in silico study using docking and molecular dynamics

• Molluscan hemocyanin, an oxygen carrier protein exhibits phenoloxidase activity.
• Docking studies reveal that the c-terminal β-domain blocks access to active site.
• Enzyme kinetics show SDS-induced enhancement in the enzyme activity of hemocyanin.
• MD studies show that SDS improves active site access by displacing the β-domain.
• Binding of phenolic substrates to hemocyanin improves after exposure to SDS.

Hemocyanin is a multimeric type-3 copper containing oxygen carrier protein that exhibits phenoloxidase-like activity and is found in selected species of arthropoda and mollusca. The phenoloxidase activity in the molluscan hemocyanins can be triggered by the proteolytic removal of the C-terminal β-rich sandwich domain of the protein or by the treatment with chemical agents like SDS, both of which enable active site access to the phenolic substrates. The mechanism by which SDS treatment enhances active site access to the substrates is however not well understood in molluscan hemocyanins. Here, using a combination of in silico molecular dynamics (MD) and docking studies on the crystal structure of Octopus dofleini hemocyanin (PDB code:1JS8), we demonstrate that the C-terminal β-domain of the protein plays a crucial role in regulating active site access to bulky phenolic substrates. Furthermore, MD simulation of hemocyanin in SDS revealed displacement of β-domain, enhanced active site access and a resulting increase in binding affinity for substrates. These observations were further validated by enzyme kinetics experiments.

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