Characterization of Starch synthase III from A. thaliana.

VALDEZ, H.; WAYLLACE, N. Z.; PARISI, G.; UGALDE, R.; BUSI, M. V.; DIEGO FABIAN GOMEZ CASATI

Rosario

Congreso; XLII Reunión SAIB; 2006

Glycogen and starch constitute the main form of storage of energy and carbon compounds in living organisms, including mammals, yeast, bacteria and plants. In plants, starch synthase (SS) catalyzes the elongation of á-(1,4) glucans by adding glucose units from the sugar-nucleotide to the non-reducing end of the growing chain. Five classes of SS were described in higher plants: granule-bound SS (GBSS), and soluble SSs (I, II, III and IV/V). All the SS members share high sequence similarity in the C-terminal catalytic domain which belongs to the glycosyltransferases 5 family (GT5). However, they differ significantly in their N-terminal domain to the extent that no sequence similarity could be found between each other.  In particular, SSIII from Arabidopsis thaliana contains an N-terminal transit peptide followed by a non-catalytic SSIII-specific domainand the common C-terminal domain common to all the SS isoforms. In this work, we report the cloning, expression and purification of full length and truncated forms of SSIII from Arabidopsis thaliana. All the proteins were purified to near homogeneity in a one-step procedure. Our results suggest that the N-terminal non-catalytic domain of SSIII play an important role in the modulation of the enzyme activity.