ANGEL2 phosphatase activity is required for non-canonical mitochondrial RNA processing

Abstract

Canonical RNA processing in mammalian mitochondria is defined by tRNAs acting as recognition sites for nucleases to release flanking transcripts. The relevant factors, their structures, and mechanism are well described, but not all mitochondrial transcripts are punctuated by tRNAs, and their mode of processing has remained unsolved. Using Drosophila and mouse models, we demonstrate that non-canonical processing results in the formation of 3′ phosphates, and that phosphatase activity by the carbon catabolite repressor 4 domain-containing family member ANGEL2 is required for their hydrolysis. Furthermore, our data suggest that members of the FAST kinase domain-containing protein family are responsible for these 3′ phosphates. Our results therefore propose a mechanism for non-canonical RNA processing in metazoan mitochondria, by identifying the role of ANGEL2.

The molecular machinery for maturation of primary mtDNA transcripts

“…An additional piece of the puzzle was recently presented when it was proposed that cleavage of non-canonical junctions results in the formation of 3′- or 2′,3′-cyclic phosphate (2′,3′-cP) residues [ 71 ]. Several ribonucleases are known to cleave the phosphodiester bond downstream of the bridging phosphorus atom, resulting in unconventional free 3′ phosphates or 2′,3′-cP, and 5′ hydroxyl groups [ 72 ].…”

“…Several ribonucleases are known to cleave the phosphodiester bond downstream of the bridging phosphorus atom, resulting in unconventional free 3′ phosphates or 2′,3′-cP, and 5′ hydroxyl groups [ 72 ]. Using fly and mouse knockout models of the carbon catabolite repressor 4 domain-containing family member CCR4D, also known as ANGEL2, it was demonstrated that Atp6/8 and Nd5 accumulate 3′ terminal phosphates, preventing their polyadenylation [ 71 ]. Furthermore, the Drosophila ortholog DmAngel (cg12273) co-precipitated with the Drosophila FASTK family member CG13850.…”

Molecular pathways in mitochondrial disorders due to a defective mitochondrial protein synthesis

“…These enzymes cleave on the 5′ and 3' end of the tRNAs respectively, releasing the mRNAs and rRNAs (Rackham et al, 2016). There are however certain gene junctions in the polycistronic mitochondrial transcripts that do not contain a tRNA and the details and protein factors involved in their processing are now starting to emerge (Ohkubo et al, 2021;Clemente et al, 2022). The newly processed RNAs need to be further modified for proper maturation and rRNAs are assembled together with the ribosome protein components to form the mature mitoribosome.…”