Structural studies of B30.2 domain of GNIP and its interaction with glycogenin

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

Simposio; Third Argentinian Symposium on Glycobiology "GlycoAR 2019"; 2019

The initiation of glycogen biosynthesis involves the self-glucosylation of glycogenin, that synthetizes a maltosaccharide upon which glycogen synthase and branching enzyme continue glucose polymerization. In a yeast two-hybrid screen for proteins that interact with glycogenin, a polypeptide designated GNIP (Glycogenin Interacting Protein), was isolated. GNIP gene generates at least four isoforms, the largest of which (GNIP1) is predicted to have an N-terminal RING domain, a B-box domain, a coiled-coil region (RBCC motif); and a C-terminal B30.2 domain. The GNIP2 isoform, containing the B30.2 domain and a segment of the coiled-coil region, was found to stimulate glycogenin self-glucosylation in vitro while the B30.2 domain (GNIPB30.2) was reported to be necessary for the interaction with the enzyme.In recent years, GNIP1 has been shown to have ubiquitin ligase activity and to be capable of autoubiquitination, with GNIPB30.2 having an essential role in this function. GNIP1 also exhibited glycogenic effect in skeletal muscle when overexpressed.While the RBCC motif is only found in the TRIM family, the B30.2 domain is also present in other unrelated proteins and is thought to mediate selective protein interactions.Here we report the three-dimensional structure of GNIPB30.2 solved in two different crystal forms (at 1.6 Å and 1.8 Å resolution). Preliminary results regarding the characterization of the interaction between GNIPB30.2 and glycogenin are also included.