Phosphoserine Charge State Drives Ion Condensation and Spatial Polyamine Presentation in Multirepeat Silaffin

Area of Science:

• Biomineralization
• Materials Science
• Biochemistry

Background:

• Diatom silaffins guide silica formation via modified repeat domains.
• The impact of post-translational modifications (PTMs) on silaffin structure is not well understood.

Purpose of the Study:

• Investigate how PTMs influence the conformational ensemble of diatom silaffins.
• Elucidate the role of phosphate charge state and ionic strength in silaffin organization.

Main Methods:

• All-atom molecular dynamics (MD) simulations of a 195-residue silaffin construct (Sil1p R1-R7).
• Simulated native and deprotonated phosphate variants under varying NaCl concentrations.
• Analyzed ensemble compaction, ion organization, and polyamine accessibility.

Main Results:

• Silaffin structure disorders from AlphaFold 3 predictions.
• Phosphate charge state, not salt concentration, dictates ensemble compaction and ion organization.
• Doubly deprotonated phosphate forms extensive Na+ shells and bridging networks, leading to a compact state with surface-exposed polyamines.

Conclusions:

• Silaffin compaction is driven by phosphate charge and ion bridging, creating structured intermediates.
• Repeat-scale organization is crucial and not evident from single-peptide studies.
• Findings advance understanding for creating hierarchical biomimetic silica materials.