Insights into the interaction of B30.2 domain of GNIP with glycogenin

MUÑOZ SOSA, CHRISTIAN J.; CURTINO, JUAN A.; CARRIZO, MARÍA E.

Congreso; LI Reunión Anual de la Sociedad Argentina de Investigación Bioquímica y Biología Molecular; 2015

Glycogenin (GN) is the autoglucosyltransferase that initiates the biosynthesis of glycogen. By self-glucosylation from UDP-glucose and Mn2+, GN synthesizes a maltosaccharide that acts as substrate for the full polymerization and branching produced by glycogen synthase and branching enzyme, respectively. Mammalian GNs have been extensively studied, however, little is known about their functional regulation. Searching for potential regulators using a yeast two-hybrid screen, an unknown protein was identified, later called GNIP (Glycogenin Interacting Protein). GNIP gene encodes at least three isoformsproduced from alternative splicing: GNIP1, GNIP2 andGNIP3. The predicted structure of GNIP1, the largest isoform, contains an N-terminal RING finger domain, a B box domain, a coiled-coil domain and a C-terminal B30.2 domain.GNIP2, the only isoform that could be expressed ina soluble form, interacts with glycogenin and increases its self-glucosylation 3-4 fold. The interaction with glycogenin is mediated by B30.2, a domain that is present in a large number of proteins with diverse functions. Since little is known about this interaction and its consequences, we have prepared the B30.2 domain of human GNIP and analyzed its effect on glycogenin activity and the dependence ofthe interaction with the oligomeric state of the enzyme. Here we describe the results obtained during these studies.