Tuning Protein Frameworks via Auxiliary Supramolecular Interactions.

Area of Science:

• Supramolecular chemistry
• Materials science
• Biocrystallography

Background:

• Protein crystals offer precise, periodic arrays of functional units with potential in biomaterials, sensing, and catalysis.
• Controlling the assembly and properties of protein-based crystalline frameworks is crucial for their application.

Purpose of the Study:

• To investigate the modulation of a porous crystalline framework composed of a cationic redox protein and an anionic macrocycle by a small cationic effector.
• To understand how effector concentration and crystallization techniques influence the resulting crystalline architectures.

Main Methods:

• Formation of ternary composites involving protein, calix[8]arene (anionic macrocycle), and a cationic effector.
• X-ray crystallography to determine detailed structural variations.
• Density Functional Theory (DFT) calculations to elucidate the mechanism of framework modulation.

Main Results:

• Ternary composites formed distinct crystalline architectures dependent on effector concentration and crystallization method.
• The effector mediated a conformational change in calix[8]arene, observed in three distinct states, altering interaction networks.
• Co-crystallization with the effector led to framework duplication and reduced porosity due to additional protein 'pillars'.

Conclusions:

• Supramolecular host-guest interactions can be used to engineer protein crystal assembly and properties.
• The identified effector-mediated 'switch' in calixarene conformation provides a mechanism for controlling crystalline framework formation.
• This study offers insights into designing protein-based materials with tunable porosity and architecture.