GNIP, a novel protein that binds and activates glycogenin, the self-glucosylating initiator of glycogen biosynthesis
GNIP, a novel protein that binds and activates glycogenin, the self-glucosylating initiator of glycogen biosynthesis
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DOI：
10.1074/jbc.m201190200
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发表时间：
2002-05-31
影响因子：
4.8
通讯作者：
Roach, PJ
中科院分区：
文献类型：
--
作者：
Skurat, AV;Dietrich, AD;Roach, PJ
糖原蛋白是一种自身糖基化蛋白，参与糖原生物合成的启动。自身糖基化导致寡糖链的形成，当寡糖链足够长时，支持糖原合酶的作用，将其延长并形成成熟的糖原分子。为了鉴定糖原蛋白的可能调节剂，采用了酵母双杂交策略。通过使用兔骨骼肌糖原作为诱饵，从人骨骼肌cDNA文库中分离出编码三种不同蛋白质的cDNA。其中两个 cDNA 分别编码糖原蛋白和糖原合酶，已知它们是相互作用蛋白。第三个 cDNA 编码未知功能的多肽，被命名为 GNIP（糖原相互作用蛋白）。 Northern 印迹分析显示 GNIP mRNA 在骨骼肌中高表达。 GNIP 基因通过选择性剪接产生至少四种同种型。最大的亚型 GNIP1 包含从 NH2 末端到 COOH 末端、一个环指、一个 B 盒、一个假定的卷曲螺旋区域和一个 B30.2 样基序。先前鉴定的蛋白质TRIM？ （含有蛋白7的三联基序）也源自GNIP基因，由RING指、B盒和卷曲螺旋区域组成。 GNIP2 和 GNIP3 亚型由卷曲螺旋区域和 B30.2 样结构域组成。通过免疫共沉淀证实了 GNIP2 和糖原蛋白之间的物理相互作用，此外 GNIP2 还被证明可以刺激糖原蛋白自身糖基化 3-4 倍。 GNIP 可能是糖原合成起始的新参与者。
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 NH2- to COOH-terminal, a RING finger, a B box, a putative coiled-coil region, and a B30.2-like motif. The previously identified protein TRIM? (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.