The Plant ATG8-binding Proteins / 生物化学与生物物理进展

ATG8-binding proteins play a key role in autophagy, selective autophagy or non-autophagy process by interacting between ATG8 and the ATG8-interacting motif (AIM) or the ubiquitin-interacting motif (UIM). There is great progress of ATG8-binding proteins in yeast and mammalian studies. However, the plant domain is still lagging behind. Therefore, the structure characteristics of plant ATG8 binding protein were firstly outlined. Unlike the single copy of ATG8 gene in yeast, many homologous genes have been identified in plant. The LIR/ AIM-docking site (LDS) of ATG8 protein contains W and L pockets and is responsible for binding to AIM. The ATG8 protein binds to UIM-containing proteins via UIM-docking site (UDS) instead of LDS. UDS is in the opposite position to LDS, so the ATG8 can bind both AIM and UIM proteins. Secondly, the structure and function of ATG8-binding proteins, especially the selective autophagy receptors, were systematically described. The protein NBR1 and Joka2, as proteaphagy receptors, guide ubiquitination protein aggregates to autophagosome for degradation by binding to AIM and ATG8 in Arabidopsis and tobacco, respectively. AtNBR1 also promotes plant immunity by binding the capsid protein of cauliflower mosaic virus and silencing suppressor HCpro of turnip mosaic virus, mediating pathogen autophagy. AtNBR1 still degrades chloroplast by microautophagy under photoinjure or chlorophagy during ibiotic stress. And the protein ORM mediates the degradation of plant immune receptor flagellin sensing 2 (FLS2) through AIM binding to ATG8. Interestingly, ATI1 and ATI2 participate in both chlorophagy and ERphagy. Otherwise, ER membrane protein AtSec62, soluble protein AtC53, and ubiquitin-fold modifier1-specific ligase 1 (UFL1) can be directly bound to ATG8 as ER autophagy receptors. As pexophagy receptor, AtPEX6 and AtPEX10 bind to ATG8 via AIM and participate in pexophagy. RPN10, as a 26S proteasome subunit, whose C-terminal UIM1 and UIM2 bind ubiquitin and ATG8, respectively, mediates the selective autophagy degradation of 26S proteasome inactivation when fully ubiquitinated. Plant-specific mitochondrial localization proteins FCS-like zinc finger (FLZ) and friendly (FMT) may also be mitophagy receptors. CLC2 binds to ATG8 via the AIM-LDS docking site and is recruited to autophagy degradation on the Golgi membrane. The tryptophan-rich sensory protein (TSPO) in Arabidopsis was involved in clearing free heme, porphyrin and plasma membrane intrinsic protein 2;7 (PIP2;7) through the combination of AIM and ATG8. The conformation of GSNOR1 changes during anoxia, exposing the interaction between AIM and ATG8, leading to selective degradation of GSNOR1. At last, the ATG8 binding proteins involved in autophagosome closure, transport and synthetic synthesis was summarized. For example, plant-specific FYVE domain protein required for endosomal sorting 1 (FREE1) is involved in the closure of autophagosomes during nutrient deficiency. Therefore, according to the recent research advances, the structure and function of plant ATG8-binding proteins were systematically summarized in this paper, in order to provide new ideas for the study of plant selective autophagy and autophagy.

Identification and Characterization of the ATG8, a Marker of Eimeria tenella Autophagy / Identificação e Caracterização do ATG8, um marcador de autofagia em Eimeria tenella

Abstract Autophagy plays an important role in maintaining cell homeostasis through degradation of denatured proteins and other biological macromolecules. In recent years, many researchers focus on mechanism of autophagy in apicomplexan parasites, but little was known about this process in avian coccidia. In our present study. The cloning, sequencing and characterization of autophagy-related gene (Etatg8) were investigated by quantitative real-time PCR (RT-qPCR), western blotting (WB), indirect immunofluorescence assays (IFAs) and transmission electron microscopy (TEM), respectively. The results have shown 375-bp ORF of Etatg8, encoding a protein of 124 amino acids in E. tenella, the protein structure and properties are similar to other apicomplexan parasites. RT-qPCR revealed Etatg8 gene expression during four developmental stages in E. tenella, but their transcriptional levels were significantly higher at the unsporulated oocysts stage. WB and IFA showed that EtATG8 was lipidated to bind the autophagosome membrane under starvation or rapamycin conditions, and aggregated in the cytoplasm of sporozoites and merozoites, however, the process of autophagosome membrane production can be inhibited by 3-methyladenine. In conclusion, we found that E. tenella has a conserved autophagy mechanism like other apicomplexan parasites, and EtATG8 can be used as a marker for future research on autophagy targeting avian coccidia.

Resumo A autofagia desempenha um papel importante na manutenção da homeostase celular através da degradação de proteínas desnaturadas e outras macromoléculas biológicas. Nos últimos anos, muitos pesquisadores se concentraram no mecanismo da autofagia em parasitas apicomplexos, mas pouco se sabe sobre esse processo na coccidia aviária. No presente estudo, a clonagem, sequenciamento e caracterização de gene relacionado à autofagia Etatg8 foram investigados pela PCR quantitativa em tempo real (RT-qPCR), mancha ocidental (WB), ensaios indiretos de imunofluorescência (IFAs) e microscopia eletrônica de transmissão (TEM), respectivamente. Os resultados mostraram que o gene Etatg8 de E. tenella possui uma ORF de 375 bp, codificando uma proteína de 124 aminoácidos com estrutura e propriedades semelhantes à de outros apicomplexos. RT-qPCR revelou que Etatg8 é expresso durante os quatro estágios de desenvolvimento de E. tenella. Entretanto, seus níveis transcricionais foram significativamente mais elevados na fase de oocisto não esporulados. Os ensaios de manchas ocidental (WB) e de imunofluorescência (IFA) mostraram que a proteína EtATG8 foi lipidada para ligar-se à membrana do autofagossomo sob condições de deficiência nutritiva (em presença de rapamicina) e se agregar no citoplasma de esporozoítas e merozoítas. No entanto, o processo de produção de membrana do autofagossomo pode ser inibido por um inibidor de autofagia (3-meetiladeninatiladenina, 3-MA). Em conclusão, foi demonstrado que E. tenella tem um mecanismo de autofagia conservado, semelhante ao de outros parasitas apicomplexos, e que EtATG8 pode ser usado como um marcador para futuras pesquisas sobre autofagia direcionada à coccidiose aviária.

Autophagy requires Tip20 in Saccharomyces cerevisiae

Autophagy is a highly conserved intracellular degradation pathway in eukaryotic cells that responds to environmentalchanges. Genetic analyses have shown that more than 40 autophagy-related genes (ATG) are directly involved in thisprocess in fungi. In addition to Atg proteins, most vesicle transport regulators are also essential for each step of autophagy.The present study showed that one Endoplasmic Reticulum protein in Saccharomyces cerevisiae, Tip20, which controlsGolgi-to-ER retrograde transport, was also required for starvation-induced autophagy under high temperature stress. Intip20 conditional mutant yeast, the transport of Atg8 was impaired during starvation, resulting in multiple Atg8 punctadispersed outside the vacuole that could not be transported to the pre-autophagosomal structure/phagophore assembly site(PAS). Several Atg8 puncta were trapped in ER exit sites (ERES). Moreover, the GFP-Atg8 protease protection assayindicated that Tip20 functions before autophagosome closure. Furthermore, genetic studies showed that Tip20 functionsdownstream of Atg5 and upstream of Atg1, Atg9 and Atg14 in the autophagy pathway. The present data show that Tip20,as a vesicle transport regulator, has novel roles in autophagy