Plant NBR1 is a selective autophagy substrate and a functional hybrid of the mammalian autophagic adapters NBR1 and p62/SQSTM1
Plant NBR1 is a selective autophagy substrate and a functional hybrid of the mammalian autophagic adapters NBR1 and p62/SQSTM1
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DOI：
10.4161/auto.7.9.16389
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发表时间：
2011-09-01
期刊：
影响因子：
13.3
通讯作者：
Johansen, Terje
中科院分区：
文献类型：
--
作者：
Svenning, Steingrim;Lamark, Trond;Johansen, Terje
（宏观）自噬包括细胞质内容物的非选择性大量降解以及受损细胞器、细胞内微生物、蛋白质聚集体、细胞结构和特定可溶性蛋白质的选择性自噬。选择性自噬由自噬适配器介导，如p62/SQSTM 1和NBR 1。p62和NBR 1本身是选择性自噬底物，但它们也作为降解其他底物的货物受体。令人惊讶的是，我们发现NBR 1的同源物分布在整个真核生物界，而p62仅限于后生动物。作为仅具有NBR 1同源物的所有生物的代表，我们更详细地研究了拟南芥NBR 1（AtNBR 1）。AtNBR 1在结构域结构和氨基酸序列上与哺乳动物NBR 1比与p62更相似。然而，与p62类似，AtNBR 1通过PB 1结构域进行均聚。因此，AtNBR 1具有哺乳动物NBR 1和p62的杂交特性。AtNBR 1具有2个乌巴结构域，但只有C-末端的乌巴结构域结合泛素。AtNBR 1通过保守的LIR（LC 3相互作用区）基序结合AtATG 8，并且需要AtATG 8或人GABARAPL 2的共表达才能在HeLa细胞中被识别为自噬底物。为了监测AtNBR 1在拟南芥中的自噬隔离，我们制作了表达AtNBR 1的转基因植物，AtNBR 1融合到pH敏感的荧光标签，红色酸不敏感的mCherry和酸敏感的黄色荧光蛋白的串联融合。这一策略使我们能够表明，AtNBR 1是一种自噬底物降解的液泡依赖于PB 1结构域的聚合特性和AtATG 7的表达。液泡输入需要功能性LIR。
(Macro)autophagy encompasses both an unselective, bulk degradation of cytoplasmic contents as well as selective autophagy of damaged organelles, intracellular microbes, protein aggregates, cellular structures and specific soluble proteins. Selective autophagy is mediated by autophagic adapters, like p62/SQSTM1 and NBR1. p62 and NBR1 are themselves selective autophagy substrates, but they also act as cargo receptors for degradation of other substrates. Surprisingly, we found that homologs of NBR1 are distributed throughout the eukaryotic kingdom, while p62 is confined to the metazoans. As a representative of all organisms having only an NBR1 homolog we studied Arabidopsis thaliana NBR1 (AtNBR1) in more detail. AtNBR1 is more similar to mammalian NBR1 than to p62 in domain architecture and amino acid sequence. However, similar to p62, AtNBR1 homo-polymerizes via the PB1 domain. Hence, AtNBR1 has hybrid properties of mammalian NBR1 and p62. AtNBR1 has 2 UBA domains, but only the C-terminal UBA domain bound ubiquitin. AtNBR1 bound AtATG8 through a conserved LIR (LC3-interacting region) motif and required co-expression of AtATG8 or human GABARAPL2 to be recognized as an autophagic substrate in HeLa cells. To monitor the autophagic sequestration of AtNBR1 in Arabidopsis we made transgenic plants expressing AtNBR1 fused to a pH-sensitive fluorescent tag, a tandem fusion of the red, acid-insensitive mCherry and the acid-sensitive yellow fluorescent proteins. This strategy allowed us to show that AtNBR1 is an autophagy substrate degraded in the vacuole dependent on the polymerization property of the PB1 domain and of expression of AtATG7. A functional LIR was required for vacuolar import.