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Recently, the Research Group of Huangof the Institute of Biochemistry and Cell Biology of the Shanghai Institute of Life Sciences of the Chinese Academy of Sciences, based on the study of The Rap insights into the sequence-specific recognition of Piwi by Drosophila Papi, published online in PNAS, revealed the molecular mechanism of the Papi protein sequence specifically identifying Piwi proteins and participating in piRNA 3 end pruning in the fruit fly piRNA pathway.
piRNA is a small type of RNA about 24-30 nt in length that protects the integrity of the host cell's genome in the body.
mature piRNA generation and processing processes include precursor generation, intermediate product processing, and piRNA 3' end trimming and methylation modification, resulting in the formation of mature piRNA.
processing at piRNA 3' end requires the involvement of papi (Tdrkh) proteins.
previous studies have shown that papi proteinas as stent proteins can, on the one hand, identify the PWIE protein N-end (G/A) R repeat sequence of Piwi proteins through its eTudor (eTud) domain to identify the arginine symmetric bimethylation modification (sDMA modification) to recruit Piwi protein, on the other hand, recruit piRNA 3'end Trimmer Trimmer to form a piRNA 3' trim end complex.
but Papi's model that identifies the Piwi N end through the eTudor domain lacks a structural basis.
past studies have found that knocking out Papi proteins in fruit flies can specifically affect the length of Piwi protein binding piRNA, while the length of the PiRNA combined with Ago3 and Aub proteins is not affected.
however, there is a lack of molecular mechanism sefactory explanations for the specific effects of Papi protein knockout on Piwi protein binding piRNA length.
in this work, the researchers pinpointed the segmentof in which the papi protein interacts with the N-end of the fruit fly through its eTud domain and Piwi protein, and the crystal structure of the Papi-eTud monomer structure, its compound with Piwi-E-R10me2s (10th arginine DMA modification) and its unmethylated Piwi-N polypeptide complex respectively.
structure reveals that Papi-eTud interacts with the "RGRRR" motif at the Piwi N end, a different motif than the previously reported (G/A) R repeat sequence in other PIWI proteins, specifically present in the fruit fly Piwi protein, and conservatively present in the fruit fly Piwi protein in different subspecies; the sequence specificity of the motif determines the specificity of the Papi-Piwi protein interaction.
experiments in fruit flies have shown that destroying the vital amino acid residues of the Papi protein interacting with Piwi leads to reproductive defects and transposons in fruit flies to inhibit.
researchers demonstrated the specificity of Papi and Piwi interactions in fruit flies through structural biology, combined with co-IP, mass spectrometry and other in vitro biochemical experiments, and provided molecular mechanisms for explaining how Papi recruited Piwi to participate in the piRNA 3' pruning process and specifically affectpiwi-combined piRNA length, extending the understanding of the sequence characteristics and binding patterns of Tudor's structural domain.
research work has been supported by the National Natural Science Foundation of China, the Chinese Academy of Sciences strategic leading science and technology projects and the Chinese Academy of Sciences major scientific and technological infrastructure open research projects.
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