FUNCTIONAL DEMONSTRATIONS OF STARCH BINDING DOMAINS PRESENT IN OSTREOCOCCUS TAURI STARCH SYNTHASES ISOFORMS

DIEGO FABIAN GOMEZ CASATI; HEDIN, N; BUSI, M. V.; BARCHIESI, J; BALLICORA, M.

Smolenice

Congreso; Alamy 6 Congress; 2016

Starch-binding domains are key modules present in several enzymesinvolved in polysaccharide metabolism. Thesenon-catalytic modules have already been described as essential forstarch-binding and the catalytic activity of starch synthase III from thehigher plant Arabidopsis thaliana. In Ostreococcus tauri, a unicellular green alga of the Prasinophyceae family, there are threeSSIII isoforms, known as Ostta SSIII-A, SSIII-B and SSIII-C. In this work, using in silico and in vitro characterization techniques, we have demonstrated that Ostta SSIII-A, SSIII-B and SSIII-C contain two,three and no starch-binding domains, respectively. Additionally, our phylogenetic analysis has indicated that OsttaSSIII-B, presenting three N-terminal SBDs, is the isoform more closelyrelated to higher plant SSIII.Furthermore, the sequence alignment and homology modeling datagathered showed that both the main 3-D structures of all the modeled domainsobtained and the main amino acid residues implicated instarch binding are well conserved in O.tauri SSIII starch-binding domains. Inaddition, adsorption assays showed thatOsttaSSIII-A D2 and SSIII-B D2 domains are the two that make the greatestcontribution to amylose and amylopectin binding, while OsttaSSIII-B D1 isalso important for starch binding.The results presented here suggest that differencesbetween OsttaSSIII-A and SSIII-B SBDs in the number of and binding of aminoacid residues may produce differential affinities for each isoform topolysaccharides. Increasing theknowledge about SBDs may lead to their employment in biomedical and industrialapplications.