Endogenous NO protects frataxin deficient Arabidopsis plants from oxidative stress

COLMAN, M. J. R.; DIEGO FABIAN GOMEZ CASATI; LAMATTINA, L.; EDUARDO ZABALETA; MARTIN, M.

Mar del Plata

Congreso; XLIII Reunión SAIB; 2007

Starch-synthase III (SSIII), one of the SS isoforms involved in plant starch metabolism was reported to have a regulatory role on the synthesis of transient starch. SSIII from A. thaliana has an N-terminal transit peptide for chloroplast localization which is followed by three repeated starch-binding domains, SBD, (SSIII residues 22 to 591) and a C-terminal domain (residues 592 to 1025) similar to bacterial glycogen synthase. To elucidate the enzymatic properties of SSIII and the function of the N- domain, we constructed recombinant full length and truncated isoforms of SSIII, lacking one, two or the three SBDs and recombinant SBDs with three (D123), two (D23) or one (D3) SBD domains. Results revealed that the presence of the SBDs confers particular properties to each isoform, increasing the apparent affinity and the Vmax for the oligosaccharide substrate. Under glycogen saturating conditions, the presence of SBDs increases progressively the apparent affinity and Vmax for ADPGlc. Studies on the N-domain confirm our previous results indicating that this region is a carbohydrate binding module and contributes to the binding of different polysaccharides. The results presented here suggest that the N- and C-terminal regions of SSIII have different functions: The N-domain is involved in the binding of the polysaccharide and the C-domain contributes to the molecular activity of the enzyme.