Quasi-planar nucleus structure in apoferritin crystallization.

Area of Science:

• Materials Science
• Biophysics
• Physical Chemistry

Background:

• First-order phase transitions, including condensation and crystallization, rely on critical nuclei formation.
• Nucleus structure significantly impacts nucleation thermodynamics and kinetics.
• Current models often assume compact, 3D nucleus structures, particularly for spherical building blocks.

Purpose of the Study:

• To investigate the structure of critical nuclei during apoferritin crystallization.
• To challenge the prevailing assumption of compact critical nucleus structures.
• To explore the implications of nucleus structure on nucleation theories.

Main Methods:

• Direct atomic force microscopy (AFM) observations of near-critical-size clusters.
• Analysis of cluster molecular arrangements.
• Comparison of cluster structure with final crystal structure.

Main Results:

• Near-critical-size clusters of apoferritin are planar, not compact.
• These clusters consist of 1-2 monomolecular layers arranged in rods.
• The molecular arrangement within clusters mirrors that of the final apoferritin crystals.

Conclusions:

• The critical nucleus structure for apoferritin crystallization is planar, deviating from compact models.
• Unexpected critical nucleus structures may be common, especially for anisotropic molecules.
• Advanced nucleation theories should consider nucleus structure as a variable parameter.