Starch-binding domains conservation in starch synthase III isoforms

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

Buenos Aires

Congreso; XLIX Reunión de la Sociedad Argentina de Investigación en Bioquímica y Biología Molecular (SAIB); 2013

SAIB

Starch-binding domains (SBDs) are key modules present innumerous polysaccharide metabolism enzymes. These modules areessential for starch-binding and catalytic activity of starch synthaseIII from A. thaliana. In Ostreococcus tauri, a unicellular green alga,there are three SSIII isoforms, known as Ostta SSIII-A, SSIII-B andSSIII-C. In silico studies show that these three isoforms containtwo, three and no N-terminal SBDs, respectively. In addition,phylogenetic analysis has indicated that OsttaSSIII-A N-terminalfragment is closely related to SSIII N-terminal sequences from othergreen microalgae. Besides, we observed variable SBDs sizes andnumbers in green algae SSIII enzymes. Furthermore, sequencealignment and homology modeling data showed that 3-D structuresobtained and the amino acid residues implicated in starch bindingare well conserved in OsttaSSIII SBD, except in OsttaSSIII-B D1,which might possibly undergo a deletion in the n N-terminal region.Preliminary results from affinity gel electrophoresis assays suggestthat OsttaSSIII SBDs displayed some promiscuity in the bindingto different polysaccharide substrates. These results not onlydiscloses significant information concerning evolutionary andstructure?function aspects of SBD domains, but are also crucial tobetter understand the metabolism of starch in algae.