IDENTIFICATION AND CHARACTERIZATION OF A NOVEL STARCH BRANCHING ENZYME FROM Ostreococcus tauri

HEDIN, N.; BARCHIESI, J.; GOMEZ CASATI, D.F.; BUSI, M.V.

Cordoba

Congreso; 52th Annual Meeting Argentine Society for Biochemistry and Molecular Biology; 2011

Sociedad Argentina de Investigación en Bioquímica y Biología Molecular

Starch branching enzyme (BE) is a highly conserved protein from plants to algae. This enzyme participates on starch granule assembly by the addition of α-1,6 glucan branches in the α-1,4 polyglucans. This modification determines the fine structure of amylopectin, andthus, the final structure of the starch granule. In this work we describe the function of a starch branching enzyme from the picoalgae Ostreococcus tauri. Although previous in silico evidence suggested that this protein is a starch debranching enzyme, structure-functionstudies confirmed that this polypeptide is a BE comprising two in tandem carbohydrate binding domains (from CBM41 and CBM48 families) at the N-terminal end of the protein followed by a C-terminal catalytic domain. The analysis of truncated isoforms shows thatthe CBMs bind differentially to starch and the distinct starch fractions. Moreover, no catalytic activity was detected in the CD alone or with the truncated forms of the protein. The results suggest that this O. tauri protein is a functional BE containing a CBM41 andCBM48 that are essential for enzyme activity and regulation.