Anionic proteins of the sea urchin Lytechinus variegatus tooth.

摘要

Biomineralization is a widespread and ancient phenomenon that involves all five kingdoms and produces a diversity of biogenic minerals. Despite the difference in minerals and species, there may be a common mechanistic feature involved in the biomineralization process. To test this hypothesis, the teeth of the invertebrate sea urchin Lytechinus varigatus were selected and compared to vertebrate mineralization systems. Acid soluble sea urchin proteins reacted positively with antibodies to vertebrate DMP1, DMP2, DSP and BSP II. These acid soluble proteins contained two low molecular weight bands that stained with Stains All stain and contained phosphoproteins with a significant P-Ser content comparable to bone phosphoprotein. A custom sea urchin tooth cDNA library was made and probed with DMP2 antibodies. The clones were sequenced and some of the unknown clones were identical. These clones coded for a 53 amino acid protein that had two hydrophobic ends and a very acidic -DDSDG-center section. This acidic section was similar to the (DSS) repeats of DMP2. The protein was called Urchin Tooth Matrix protein 6.5 (UTM 6.5) and a synthetic protein and antibodies were made to the acidic central section and part of the C-terminal hydrophobic arm. Primers were made to the coding sequence of UTM 6.5 and the sequence was found in the sea urchin tooth mRNA. Western blots of guanidine soluble and HCl soluble sea urchin tooth proteins reacted positively to anti-UTM 6.5 antibodies with the guanidine soluble proteins showing very strong staining in three low molecular weight bands. This data along with modeling of UTM 6.5 seemed to indicate that it is a membrane bound protein with the acidic portion outside of the membrane. Immunohistochemistry on sea urchin tooth cross-sections revealed that anti-DMP2 reacted with the syncytial cell nuclei while anti-UTM 6.5 was strongly concentrated on the syncytial membranes adjacent to the developing mineral. Thus it appears that sea urchin tooth contains mineralization proteins with epitopes similar to those of vertebrate mineralization proteins. While the mineral formed is different, invertebrates and vertebrates may use similar mineralization strategies.