Functional demonstration of starch binding domains present in Ostreococcus tauri starch synthases isoforms

JULIETA BARCHIESI; NICOLAS HEDIN; DIEGO GOMEZ-CASATI; MIGUEL BALLICORA; MA. VICTORIA BUSI

Bratislava

Congreso; Alamy 6 Congress; 2016

Starch-binding domains are key modules present in several enzymes involved in polysaccharide metabolism. These noncatalyticmodules have already been described as essential for starch-binding and the catalytic activity of starch synthaseIII from the higher plant Arabidopsis thaliana. In Ostreococcus tauri, a unicellular green alga of the Prasinophyceae family,there are three SSIII isoforms, known as Ostta SSIII-A, SSIII-B and SSIII-C. In this work, using in silico and in vitrocharacterization techniques, we have demonstrated that Ostta SSIII-A, SSIII-B and SSIII-C contain two, three and nostarch-binding domains, respectively. Additionally, our phylogenetic analysis has indicated that OsttaSSIII-B, presentingthree N-terminal SBDs, is the isoform more closely related to higher plant SSIII. Furthermore, the sequence alignment andhomology modeling data gathered showed that both the main 3-D structures of all the modeled domains obtained and themain amino acid residues implicated in starch binding are well conserved in O. tauri SSIII starch-binding domains. Inaddition, adsorption assays showed that OsttaSSIII-A D2 and SSIII-B D2 domains are the two that make the greatestcontribution to amylose and amylopectin binding, while OsttaSSIII-B D1 is also important for starch binding. The resultspresented here suggest that differences between OsttaSSIII-A and SSIII-B SBDs in the number of and binding of aminoacid residues may produce differential affinities for each isoform to polysaccharides. Increasing the knowledge aboutSBDs may lead to their employment in biomedical and industrial applications.