Sequence and atomic-force microscopy analysis of a matrix protein from the shell of the oyster Crassostrea virginica

Atomic-force microscopy of the major class of soluble matrix protein from the oyster Crassostrea virginica revealed that this protein forms a ring structure, perhaps rendering the NH₂-terminus unavailable to Edman degradation. Cleavage of these proteins using mild acid hydrolysis and hydroxylamine produced linear peptides that were able to be sequenced. Peptides consisted of a domain of polyserine-phosphoserine and runs of aspartic acid of 4 to 7 residues, with several other amino acids present. Hydrophobic domains were also isolated. Although phylogenetically distant, oyster shell-matrix protein is similar to the phosphophoryn isolated from dentin and, to a lesser extent, proteins isolated from verteorate bone.