Preferential binding of SBD from Arabidopsis thaliana SSIII to polysaccharides: Study of amino acid residues involved

VALDEZ, H.A.; PERALTA, D.A.; WAYLLACE NZ; GRISOLÍA, M. J.; GOMEZ-CASATI, D. F.; BUSI M. V.

Starch

WILEY-VCH

Lugar: weinheim; Año: 2011 vol. 63 p. 451 - 460

1521-379X

Abstract SS III (SSIII) has been reported to play a regulatory role in the synthesis of transient starch. SSIII from Arabidopsis thaliana contains 1025 amino acid residues and has an N-terminal transit peptide for chloroplast localization followed by three in tandem starch-binding domains (SBDs D1, D2, and D3, residues 22-591). Its C-terminal catalytic domain (residues 592?1025) is similar to bacterial glycogen synthase. Binding studies to raw starch and its individual components, AM or AP show that the SBD region binds preferentially to AM, and that the D1 domain is mainly responsible for this selective binding. The D2 domain contains two binding sites which include amino acid residues Y394 (binding site 1) and W366 (binding site 2) acting cooperatively with the D1 domain in the binding process while G335 and W340 have a minor role. In addition, mutations in these residues also affect the kinetic parameters for the polysaccharide substrate of SSIII.