OLIGOPHOSPHOPEPTIDES OF VARIED STRUCTURAL COMPLEXITY DERIVED FROM THEEGG PHOSPHOPROTEIN, PHOSVITIN

Phosvitins are the principal phosphoproteins in the eggs of oviparous vertebrates. They have an exceptionally high serine content and most, or even all, of the serine residues are esterified to phosphate. The p hosphorylated residues tend to occur in uninterrupted runs of as many as 28 phosphoserines (as in Xenopus phosvitin). This unique structural feature gives phosvitins extraordinary properties and can be expected to play a key role in phosvitin function. For example, the concentrat ion of phosphate groups provides for numerous highly efficient metal-b inding sites in clusters. The mode of binding had been shown to be aff ected by the size of the protein and the degree to which serine residu es are phosphorylated. For structure-function studies of phosvitins (a nd other polyphosphoproteins), phosphopeptides of differentiated struc tural complexity are desirable. Such model peptides were produced in t his work by limited proteolysis of chicken phosvitin, and oligophospho peptides of widely varying sizes, phosphoserine content, and sequence were purified and characterized. These include phosvitin segments cont aining one, two, or several oligophosphoserine runs, corresponding to segments of the N-terminal, C-terminal, and core sequence of the prote in.