Starch-binding domains conservation in starch synthase III isoforms

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

Buenos Aires

Congreso; Reunión de la Sociedad Argentina de Investigación en Bioquímica y Biología Molecular; 2013

Starch-binding domains (SBD) are key modules present in numerous polysaccharide metabolism enzymes. These modules are essential for starch-binding and catalytic activity of starch synthase III from A. thaliana. In Ostreococcus tauri, a unicellular green alga, there are three SSIII isoforms, known as OtSSIII-A, SSIII-B and SSIII-C. In this work, using in silico characterization techniques, we have shown that these three isoforms contain two, three and no N-terminal SBD, respectively. In addition, our phylogenetic analysis has indicated that OtSSIII-A N-terminal fragment is closely related to SSIII N-terminal sequences from other green microalgae. Besides, we observed variable SBD sizes and numbers in green algae SSIII enzymes. Furthermore, sequence alignment and homology modeling data gathered showed that 3-D structures obtained and the amino acid residues implicated in starch binding are well conserved in OtSSIII SBD, except in OtSSIII-B D1, which might possibly unde rgo a N-terminal region deletion. Preliminary results from affinity assays su ggest than OtSSIII SBDs displayed some promiscuity in binding to different polysaccharide substrates. These results not only discloses significant information concerning evolutionary and structure ?function aspects of SBD domains, but are also crucial to approaching the main subject of algae starch metabolism.