4ggj
From Proteopedia
Crystal structure of Zucchini from mouse (mZuc / PLD6 / MitoPLD)
Structural highlights
Function[PLD6_MOUSE] Regulates mitochondrial shape through facilitating mitochondrial fusion. During spermatogenesis, plays a critical role in PIWI-interacting RNA (piRNA) biogenesis. piRNAs provide essential protection against the activity of mobile genetic elements. piRNA-mediated transposon silencing is thus critical for maintaining genome stability, in particular in germline cells when transposons are mobilized as a consequence of wide-spread genomic demethylation. Has been proposed to act as a cardiolipin hydrolase to generate phosphatidic acid at mitochondrial surface (PubMed:21397848). Although it cannot be excluded that it can act as a phospholipase in some circumstances, it should be noted that cardiolipin hydrolase activity is either undetectable in vitro (PubMed:23064227 and PubMed:23064230), or very low. In addition, cardiolipin is almost exclusively found on the inner mitochondrial membrane, while PLD6 localizes to the outer mitochondrial membrane, facing the cytosol. Has been shown to be a backbone-non-specific, single strand-specific nuclease, cleaving either RNA or DNA substrates with similar affinity (PubMed:23064227 and PubMed:23064230). Produces 5' phosphate and 3' hydroxyl termini, suggesting it could directly participate in the processing of primary piRNA transcripts.[1] [2] [3] [4] Publication Abstract from PubMedPIWI-family proteins and their associated small RNAs (piRNAs) act in an evolutionarily conserved innate immune mechanism to provide essential protection for germ-cell genomes against the activity of mobile genetic elements. piRNA populations comprise a molecular definition of transposons, which permits them to distinguish transposons from host genes and selectively silence them. piRNAs can be generated in two distinct ways, forming either primary or secondary piRNAs. Primary piRNAs come from discrete genomic loci, termed piRNA clusters, and seem to be derived from long, single-stranded precursors. The biogenesis of primary piRNAs involves at least two nucleolytic steps. An unknown enzyme cleaves piRNA cluster transcripts to generate monophosphorylated piRNA 5' ends. piRNA 3' ends are probably formed by exonucleolytic trimming, after a piRNA precursor is loaded into its PIWI partner. Secondary piRNAs arise during the adaptive 'ping-pong' cycle, with their 5' termini being formed by the activity of PIWIs themselves. A number of proteins have been implicated genetically in primary piRNA biogenesis. One of these, Drosophila melanogaster Zucchini, is a member of the phospholipase-D family of phosphodiesterases, which includes both phospholipases and nucleases. Here we produced a dimeric, soluble fragment of the mouse Zucchini homologue (mZuc; also known as PLD6) and show that it possesses single-strand-specific nuclease activity. A crystal structure of mZuc at 1.75 A resolution indicates greater architectural similarity to phospholipase-D family nucleases than to phospholipases. Together, our data suggest that the Zucchini proteins act in primary piRNA biogenesis as nucleases, perhaps generating the 5' ends of primary piRNAs. The structural biochemistry of Zucchini implicates it as a nuclease in piRNA biogenesis.,Ipsaro JJ, Haase AD, Knott SR, Joshua-Tor L, Hannon GJ Nature. 2012 Nov 8;491(7423):279-83. doi: 10.1038/nature11502. Epub 2012 Oct 14. PMID:23064227[5] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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