Cuticular proteins from the blue crab alter in vitro calcium carbonate mineralization

Extracellular proteins have long been implicated in the control of mineralization. Cuticular proteins of the blue crab, Callinectes sapidus, undergo changes concurrent with mineralization after molting. A pH drift in vitro mineralization assay was used to assess the effects of cuticular extracts on the inhibition of crystal deposition and the morphology of the resulting crystals. Crystal nucleation was strongly delayed by material extracted into 2% acetic acid within the first 1.5 h post-ecdysis. This effect was not seen with other extracts. No consistent effects of the cuticular extracts on calcium carbonate crystal morphology were observed. Proteins associating with these crystals were extracted and subjected to electrophoresis. These crystal-associated proteins (CAPs) differed depending upon the extraction method and the time after ecdysis when the crab was sacrificed. The early acetic acid extracts produced a unique combination of CAP bands at 66, 42 and 24 kDa. These results are consistent with a model of mineralization in C. sapidus involving (a) certain proteins serving as nucleation sites and attached to the cuticle at all times by acid labile bonds, and (b) other proteins acting as inhibitors of crystal nucleation until being altered at approximately 1 h post-ecdysis. (C) 1998 Elsevier Science Inc. All rights reserved.