Abstract
In the present study, we enumerate and characterize the proteins that comprise the integral spicule matrix of the Strongylocentrotus purpuratus embryo. Two-dimensional gel electrophoresis of [35S]methionine radiolabeled spicule matrix proteins reveals that there are 12 strongly radiolabeled spicule matrix proteins and approximately three dozen less strongly radiolabeled spicule matrix proteins. The majority of the proteins have acidic isoelectric points; however, there are several spicule matrix proteins that have more alkaline isoelectric points. Western blotting analysis indicates that SM50 is the spicule matrix protein with the most alkaline isoelectric point. In addition, two distinct SM30 proteins are identified in embryonic spicules, and they have apparent molecular masses of approximately 43 and 46 kDa. Comparisons between embryonic spicule matrix proteins and adult spine integral matrix proteins suggest that the embryonic 43-kDa SM30 protein is an embryonic isoform of SM30. An adult 49-kDa spine matrix protein is also identified as a possible adult isoform of SM30. Analysis of the SM30 amino acid sequences indicates that a portion of SM30 proteins is very similar to the carbohydrate recognition domain of C-type lectin proteins.
Highlights
During the course of its development a sea urchin embryo constructs a pair of calcareous endoskeletal spicules
The 8 –10 bands previously identified by Benson et al [16] and Venkatesan and Simpson [17] as S. purpuratus spicule matrix proteins have apparent molecular masses similar to many of the proteins separated by the two-dimensional gels presented here
Acidic integral matrix proteins isolated from calcitic adult sea urchin exoskeletal tissues have been shown to bind to specific faces of calcite crystal in vitro [4]
Summary
During the course of its development a sea urchin embryo constructs a pair of calcareous endoskeletal spicules. It is apparent most of the proteins are acidic, with molecular masses ranging from about 20 to over 100 kDa. The 8 –10 bands previously identified by Benson et al [16] and Venkatesan and Simpson [17] as S. purpuratus spicule matrix proteins have apparent molecular masses similar to many of the proteins separated by the two-dimensional gels presented here.
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