More than 90% of nacre matrix proteins are composed of silk-like proteins

Abstract

A proteome is a powerful tool to study nacre biomineralization that occurs in an ordered microenvironment composed mainly of proteins and polysaccharides. As more and more proteins are detected, new questions arise about which proteins are responsible for forming this microenvironment. In this study, shell matrix proteins (SMPs) of nacre were analyzed using label-free quantitative proteome. A total of 99.89% of the insoluble nacre SMPs were composed of silk-like proteins, chitin-binding proteins, and cysteine-rich SMPs, which were responsible for organic framework assembly. A total of 99.34% of the soluble nacre SMPs were composed of silk-like proteins and chitin-binding proteins, which were responsible for forming protein gel filling in organic frameworks. The content of silk-like proteins was more than 90% in both insoluble and soluble nacre SMPs. As organic frameworks and protein gel together constructed a microenvironment for calcium carbonate biomineralization, these results provided a novel understanding of nacre formation.