CRYSTAL PROTEIN INTERACTIONS STUDIED BY OVERGROWTH OF CALCITE ON BIOGENIC SKELETAL ELEMENTS

A key parameter in the biological control of crystal formation is the interaction of a group of acidic macromolecules with the mineral phase . Here we study protein-calcite interactions using epitaxial overgrowt h of synthetic calcite crystals under conditions in which local releas e of occluded macromolecules from the biogenic substrate occurs. The m acromolecules subsequently interact with the newly formed overgrown cr ystals, resulting in modified calcite morphology. This novel method pr ovides a means of mapping crystal-protein interactions under condition s that minimally affect the conformational states of the acidic macrom olecules. We show that proteins released from calcitic sponge spicules and mollusc prisms specifically interact with {001} and {01l} faces o f calcite, whereas proteins released from echinoderm skeletal elements only interact with {01l} faces. The extent to which the overgrown cry stals are affected by the proteins varies even in the same organism an d within the same element, depending on the site and crystallographic orientation of the skeletal elements.