Starch-Synthase III family encodes a tandem of three starch-binding domains

PALOPOLI, N.; BUSI, M. V.; FORNASARI, M. S.; DIEGO FABIAN GOMEZ CASATI; PARISI, G.; UGALDE, R.

Pinamar

Congreso; XLI Reunión Sociedad Argentina de Investigación en Bioquímica y Biología Molecular (SAIB); 2005

The starch-synthase III (SSIII) is one of the enzymes that participate in the synthesis of starch in plants. SSIII from Arabidopsis thaliana contains a 557-amino acid N-terminal SSIII-specific domain with three internal repeats. Based on similarity searches, fold class assignment methods and homology modeling, we found that each of the repeats encodes for a starch-binding domain (SBD). Although the SSIII from A. thaliana and its plants and algae homologous show no detectable sequence similarity with characterized SBD, the sequential and spatial conservation of residues known to be involved in binding of starch gives a further support for this assignment. As the majority of SBD are found in degrading starch and glycogen microbial enzymes, this is the first report of an SBD both in plants and in a synthesizing enzyme. This results offer important information not only for the evolutionary and functional-structural aspects of the SBD domain, but also for physiological issues in plant starch metabolism.