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

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

BMC Research Notes

BIOMED CENTRAL LTD

Lugar: Londres; Año: 2015 vol. 8 p. 1 - 12

Background: Starch-binding domains are key modules present in several enzymes involved in polysaccharidemetabolism. These non-catalytic modules have already been described as essential for starch-binding and the catalyticactivity of starch synthase III from the higher plant Arabidopsis thaliana. In Ostreococcus tauri, a unicellular greenalga of the Prasinophyceae family, there are three SSIII isoforms, known as Ostta SSIII-A, SSIII-B and SSIII-C.Results: In this work, using in silico and in vitro characterization techniques, we have demonstrated that Ostta SSIIIA,SSIII-B and SSIII-C contain two, three and no starch-binding domains, respectively. Additionally, our phylogeneticanalysis has indicated that OsttaSSIII-B, presenting three N-terminal SBDs, is the isoform more closely related to higherplant SSIII. Furthermore, the sequence alignment and homology modeling data gathered showed that both the main3-D structures of all the modeled domains obtained and the main amino acid residues implicated in starch bindingare well conserved in O. tauri SSIII starch-binding domains. In addition, adsorption assays showed that OsttaSSIII-A D2and SSIII-B D2 domains are the two that make the greatest contribution to amylose and amylopectin binding, whileOsttaSSIII-B D1 is also important for starch binding.Conclusions: The results presented here suggest that differences between OsttaSSIII-A and SSIII-B SBDs in thenumber of and binding of amino acid residues may produce differential affinities for each isoform to polysaccharides.Increasing the knowledge about SBDs may lead to their employment in biomedical and industrial applications.