Abstract
The marine unicellular algae, coccolithophorids produce a calcified biomineral named coccolith. Coccolith has a fine and elaborate ultrastructure of calcium carbonate crystals. In Emiliania huxleyi, a unique acid polysaccharide, coccolith polysaccharide (CP) composed of α-1,3-mannose in the main chain, is located on the coccolith and in coccolith producing vesicles. Therefore, CP has been suggested to be involved in coccolith formation. In order to study on CP biosynthesis, we tried to identify a cDNA of key enzyme in CP biosynthesis from Emiliania EST database and cloned a putative cDNA of GDP-Mannose pyrophosphorylase providing GDP-mannose, a substrate for α-1,3-mannose synthesis. The deduced protein sequence was 382 a.a. (40.9 kDa) in size, and was highly homologous to the known GDP-mannose pyrophosphorylase. This is the first identification of cDNA related to CP synthesis. Regulation of its induction may become a useful tool for the study of the molecular mechanism of coccolith crystallization.
