The intramolecular autoglucosylation of monomeric and dimeric glycogenin

ISSOGLIO, FEDERICO M.; BAZÁN, SOLEDAD; CARRIZO, MARÍA E.; CURTINO, JUAN A.

Carlos Paz, Córdoba, Argentina

Congreso; XLIV Reunión Anual de la Sociedad Argentina de Investigación Bioquímica y Biología Molecular (SAIB); 2008

Sociedad Argentina de Investigación Bioquímica y Biología Molecular (SAIB)

It was described that glycogenin exists in solution and crystallizes as dimer at high protein concentrations. These results, together with the enzyme concentration independent specific rate of glucosylation, lead to propose an inter-subunit, intradimeric reaction mechanism for autoglucosylation. We analyzed the size of glycogenin by gel filtration and the specific rate of autoglucosylation at low protein concentrations and describe that the enzyme exist as monomer at low concentrations, showing a glucosylation kinetics also consistent with an intramolecular reaction mechanism. Accordingly, the dimeric glycogenin subunit might glucosylate as the monomer do, by a similar intra-molecular instead of intermolecular, intersubunit mechanism. The specific rate of autoglucosylation of the dimeric enzyme is up to two times the rate of the monomeric form. Referring to which form, monomer or dimer, would actually initiate the autoglucosylation in vivo, it is conceivable that just after synthesized, a molecule of glycogenin initiates its autoglucosylation without the need to reach the concentration required for dimerization. The monomer to dimer conversion resulting in the increase of the autoglucosylation efficiency, would allow glycogenin to modulate the de novo biosynthesis of proteoglycogen at the initial step of the glucose polymerization.