Natural hybrid silica/protein superstructure at atomic resolution

Area of Science:

• Biomineralization
• Structural Biology
• Materials Science

Background:

• Demosponges form silica spicules via a biomineralization process guided by protein scaffolds.
• Silicateins are key enzymes in this process, forming hybrid silica/protein structures.
• The tertiary structure of silicatein, vital for its function, remained unknown.

Purpose of the Study:

• To determine the atomic structure of silicatein and its associated mineral/organic assembly.
• To elucidate the mechanism of spicule formation and silicatein's role in vivo.
• To understand the crystallization and superstructure formation of silicatein.

Main Methods:

• Serial X-ray crystallography was employed to analyze 2-µm-thick filaments in situ.
• High-resolution transmission electron microscopy (HR-TEM) was used for imaging and chemical analysis.
• Combined techniques provided insights into enzymatic activity and structural assembly.

Main Results:

• The atomic structure of silicatein and the hybrid silica/protein assembly was resolved at 2.4 Å.
• Detailed information on silicatein's enzymatic activity, crystallization, and superstructure formation was obtained.
• A functional, three-dimensional silica/protein superstructure was observed in vivo.

Conclusions:

• The study provides the first atomic-resolution structure of silicatein and its biomineralization complex.
• This reveals the mechanism by which silicatein directs silica morphogenesis in spicules.
• The findings offer insights into naturally occurring crystalline mineral/protein assemblies with biotechnological potential.