Role of biopolymers in hard tissue generation in organism

POLY 377

Suresh Valiyaveettil, chmsv@nus.edu.sg, Singapore-MIT Alliance, National University of Singapore, 3 Science Drive, Singapore 117543, Singapore
It is believed that highly organized biomacromolecules perform sophisticated functions in living organisms. We are slowly beginning to understand the structure - function relationship of these complex molecules. Recently, we reported the purification and characterization of a few novel eggshell specific proteins, extracted from eggshell matrix. Ansocalcin (extracted from goose eggshell) showed ~53% homology to ovocleidin 17 (OC 17), the eggshell specific protein from chicken eggshell. To understand the role of ansocalcin and OC 17 in eggshell calcification, we carried out in vitro crystal growth experiment of calcium carbonate in presence of these two proteins. Our results indicate that the proteins interact differently with calcium carbonate crystals. The crystal growth pattern was little affected by OC 17. At lower concentrations, it induced crystals exhibiting protrusions along {10.4} faces. At higher concentrations the crystal surfaces were severely roughened followed by appearance of microscopic (0.5-2 m) sized pores. At this level OC-17 was deposited on some of the crystals, whereas crystals grown in presence of ansocalcin showed strong changes in the pattern and morphology depending on the concentration. At lower concentrations of ansocalcin, spiral pits were formed on the calcite surfaces, with increase in concentration, spherical polycrystalline aggregates and at the highest concentrations spheroidal and ellipsoidal aggregates were observed. We propose that ansocalcin associates to form dimers and trimers in solution which acts as a template inducing calcite aggregation.