Department of Biochemistry and Molecular Biology, Indiana University School of Medicine, Indianapolis, IN 46202, USA.
Biochem Biophys Res Commun. 2011 Sep 30;413(3):420-5. doi: 10.1016/j.bbrc.2011.08.106. Epub 2011 Aug 27.
Glycogen, a branched polymer of glucose, acts as an intracellular carbon and energy reserve in many tissues and cell types. An important pathway for its degradation is by transport to lysosomes in an autophagy-like process. It has been proposed that starch-binding domain-containing protein 1 (Stbd1) may participate in this mechanism by anchoring glycogen to intracellular membranes. In addition, Stbd1 has been reported to interact with a known autophagy protein, GABARAPL1, a member of the Atg8 family. Here, we confirm this interaction and identify an Atg8 interacting motif (AIM) in Stbd1 necessary for GABARAPL1 binding as judged by co-immunoprecipitation from cell extracts and co-localization in cells as evidenced by immunofluorescence microscopy. The AIM sequence of Stbd1 (200)HEEWEMV(206) lies within a predicted disordered region of the molecule and fits the consensus of other AIM sequences in cargo-specifying proteins such as p62 and Nix. Mutation of the AIM, including single point mutations of either W203 or V206, eliminated the co-localization of Stbd1 with both over-expressed and endogenous GABARAPL1. Stbd1 may therefore function as a novel cargo binding protein that delivers glycogen to lysosomes in an autophagic pathway that could be termed "glycophagy".
糖原是葡萄糖的支链聚合物，在许多组织和细胞类型中作为细胞内的碳源和能量储备。其降解的一个重要途径是通过自噬样过程运输到溶酶体。有人提出，淀粉结合域蛋白 1（Stbd1）可能通过将糖原锚定在内质网膜上来参与这一机制。此外，据报道，Stbd1 与已知的自噬蛋白 GABARAPL1 相互作用，GABARAPL1 是 Atg8 家族的一员。在这里，我们证实了这种相互作用，并鉴定了 Stbd1 中的一个 Atg8 相互作用基序（AIM），该基序对于 GABARAPL1 的结合是必需的，这可以通过细胞提取物中的共免疫沉淀和免疫荧光显微镜证实的细胞内共定位来判断。Stbd1 的 AIM 序列（200）HEEWEMV（206）位于分子的一个预测无序区域内，符合其他货物指定蛋白（如 p62 和 Nix）中的 AIM 序列的共识。AIM 的突变，包括 W203 或 V206 的单点突变，消除了 Stbd1 与过表达和内源性 GABARAPL1 的共定位。因此，Stbd1 可能作为一种新型货物结合蛋白，将糖原输送到自噬途径中的溶酶体中，这种自噬途径可以称为“糖噬作用”。
