An enzyme with a length proof-reading activity as a mechanism to control the size of polysaccharides.

CIOCCHINI, ANDRÉS E.; GUIDOLIN, L. SOLEDAD; CASABUONO, ADRIANA C.; COUTO, ALICIA S.; IÑÓN DE IANNINO, NORA; UGALDE, RODOLFO A.

Mar del Plata, Buenos Aires, Argentina.

Congreso; XLIII Reunión Anual de la Sociedad Argentina de Investigaciones en Bioquímica y Biología Molecular" (SAIB 2007).; 2007

Sociedad Argentina de Investigaciones en Bioquímica y Biología Molecular.

Cyclic b-1,2-glucans are osmolite homopolysaccharides with a cyclic b-1,2-glucan backbone of 17 to 25 glucose residues present in the periplasmic space of several bacteria. Initiation, elongation and cyclization, the three distinctive reactions required for building the cyclic structure, are catalyzed by the same protein, the cyclic b-1,2-glucan synthase (Cgs). The initiation activity catalyzes the transference of the first glucose from UDP-glucose to a yet unidentified amino acid residue in the same protein. Elongation proceeds by the successive addition of glucose residues from UDP-glucose to the non-reducing end of the protein-linked b-1,2-oligosaccharide intermediate. Finally, the protein-linked intermediate is cyclized and the cyclic glucan released from the protein. These reactions do not explain, however, the mechanism by which the number of glucose residues in the cyclic structure is controlled. We now report that control of the degree of polymerization (DP) is carried out by a b-1,2-glucan phosphorylase present at the Cgs C-terminal domain. This last activity catalyzes the phosphorolysis of the b-1,2-glucosidic bond at the non-reducing end of the linear protein-linked intermediate releasing glucose 1-phosphate. The DP is thus regulated by this ?length proof-reading? activity. To our knowledge, this is the first description of a control of the DP of homopolysaccharides.