title: GNIP, a novel protein that binds and activates glycogenin, the self-glucosylating initiator of glycogen biosynthesis.
abstract: Glycogenin is a self-glucosylating protein involved in the initiation of glycogen biosynthesis. Self-glucosylation leads to the formation of an oligosaccharide chain, which, when long enough, supports the action of glycogen synthase to elongate it and form a mature glycogen molecule. To identify possible regulators of glycogenin, the yeast two-hybrid strategy was employed. By using rabbit skeletal muscle glycogenin as a bait, cDNAs encoding three different proteins were isolated from the human skeletal muscle cDNA library. Two of the cDNAs encoded glycogenin and glycogen synthase, respectively, proteins known to be interactors. The third cDNA encoded a polypeptide of unknown function and was designated GNIP (glycogenin interacting protein). Northern blot analysis revealed that GNIP mRNA is highly expressed in skeletal muscle. The gene for GNIP generates at least four isoforms by alternative splicing. The largest isoform GNIP1 contains, from NH(2)- to COOH-terminal, a RING finger, a B box, a putative coiled-coil region, and a B30.2-like motif. The previously identified protein TRIM7 (tripartite motif containing protein 7) is also derived from the GNIP gene and is composed of the RING finger, B box, and coiled-coil regions. The GNIP2 and GNIP3 isoforms consist of the coiled-coil region and B30.2-like domain. Physical interaction between GNIP2 and glycogenin was confirmed by co-immunoprecipitation, and in addition GNIP2 was shown to stimulate glycogenin self-glucosylation 3-4-fold. GNIPs may represent a novel participant in the initiation of glycogen synthesis.
authors.affiliation: Department of Biochemistry and Molecular Biology and Center for Diabetes Research, Indiana University School of Medicine, Indianapolis, Indiana 46202, USA.
authors.forename: Alexander V
authors.initials: AV
authors.lastname: Skurat
authors.forename: Amy D
authors.initials: AD
authors.lastname: Dietrich
authors.forename: Lanmin
authors.initials: L
authors.lastname: Zhai
authors.forename: Peter J
authors.initials: PJ
authors.lastname: Roach
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D015152:Blotting, Northern; D019556:COS Cells; D002352:Carrier Proteins / Q000096:biosynthesis* / Q000737:chemistry*; D003001:Cloning, Molecular; D003593:Cytoplasm / Q000378:metabolism; D018076:DNA, Complementary / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D005964:Glucosyltransferases; D006003:Glycogen / Q000378:metabolism*; D006023:Glycoproteins / Q000737:chemistry* / Q000378:metabolism*; D006801:Humans; D007700:Kinetics; D051379:Mice; D008969:Molecular Sequence Data; D018482:Muscle, Skeletal / Q000378:metabolism; D010957:Plasmids / Q000378:metabolism; D011233:Precipitin Tests; D011485:Protein Binding; D020033:Protein Isoforms; D017434:Protein Structure, Tertiary; D011817:Rabbits; D011994:Recombinant Proteins / Q000378:metabolism; D017386:Sequence Homology, Amino Acid; D014018:Tissue Distribution; D014162:Transfection; D000070584:Tripartite Motif Proteins; D020798:Two-Hybrid System Techniques; D044767:Ubiquitin-Protein Ligases
chemical_list: D002352:Carrier Proteins; D018076:DNA, Complementary; D006023:Glycoproteins; D020033:Protein Isoforms; D011994:Recombinant Proteins; D000070584:Tripartite Motif Proteins; C051887:glycogenin; D006003:Glycogen; C458504:TRIM7 protein, human; D044767:Ubiquitin-Protein Ligases; D005964:Glucosyltransferases