Reversible, β-sheet-dependent self-assembly of the phosphoprotein phosvitin is controlled by the concentration and valency of cations

Phys Chem Chem Phys. 2022 May 18;24(19):11791-11800. doi: 10.1039/d1cp05493g.


The hyperphosphorylated protein phosvitin (PV) undergoes a pH-dependent transition between PII- and β-sheet secondary structures, a process deemed crucial for its role in the promotion of biogenic apatite formation. The transition occurs surprisingly slowly (minutes to hours). This is consistent with a slow aggregation process involving ionic interactions of charged groups on the protein surface. Herein, we determined the associated transition pK values and time constants through matrix least-squares (MLS) global fitting of a series of pH- and time-dependent circular dichroism (CD) spectra recorded in the presence of different mono-, bi- and trivalent cations. Supporting our results with dynamic light scattering data, we clearly identified a close correlation of β-sheet transition and the formation of small aggregates at low pH. This process is inhibited in the presence of all tested cations with the strongest effects for trivalent cations (Fe3+ and Al3+). In the presence of Ca2+ and Mg2+, larger higher-order particles are formed from PV in the β-sheet conformation, as identified from the interpretation of differential scattering observed in the CD spectra. Our observations are consistent with the existence of a multi-step equilibrium between aggregated and non-aggregated species of PV. The equilibrium is highly sensitive to the environment pH and salt concentration with exceptional behavior in the presence of divalent cations such as Ca2+ and Mg2+.

MeSH terms

  • Cations, Divalent / chemistry
  • Circular Dichroism
  • Hydrogen-Ion Concentration
  • Phosphoproteins*
  • Phosvitin*
  • Protein Conformation, beta-Strand
  • Protein Structure, Secondary


  • Cations, Divalent
  • Phosphoproteins
  • Phosvitin