conchiolin

Conchiolin is a term used for a family of secreted molluscan proteins that form part of the shell’s organic matrix, most prominently in the periostracum, the outer organic layer that covers the calcium carbonate skeleton. It is produced by the mantle and secreted into the extrapallial space during shell formation, where it serves as a scaffold for subsequent mineral deposition.

Composition and properties of conchiolin vary among species, but it is typically rich in sulfur-containing amino acids such as cysteine. The high cysteine content allows disulfide cross-linking, which helps produce a flexible, durable organic framework. Conchiolin is largely insoluble in water and mild solvents, and can be solubilized or disrupted by reducing agents that break disulfide bonds.

Functions in shell formation and structure include providing a protective organic layer that shields underlying mineral phases and guiding the growth of calcium carbonate crystals. In many mollusks, conchiolin forms part of the periostracum and contributes to the overall mechanical properties of the shell by interacting with other organic components such as chitin and various shell proteins.

The precise composition of conchiolin is not uniform across all mollusks, reflecting species-specific variations in secreted proteins. Its study contributes to the broader field of biomineralization and has implications for materials science, where synthetic analogs of natural organic matrices inspire durable, lightweight composites.

See also: mollusk shell, periostracum, nacre, biomineralization.