RNase P without RNA: Identification and Functional Reconstitution of the Human Mitochondrial tRNA Processing Enzyme

Abstract

tRNAs are synthesized as immature precursors, and on their way to functional maturity, extra nucleotides at their 5' ends are removed by an endonuclease called RNase P. All RNase P enzymes characterized so far are composed of an RNA plus one or more proteins, and tRNA 5' end maturation is considered a universal ribozyme-catalyzed process. Using a combinatorial purification/proteomics approach, we identified the components of human mitochondrial RNase P and reconstituted the enzymatic activity from three recombinant proteins. We thereby demonstrate that human mitochondrial RNase P is a protein enzyme that does not require a trans-acting RNA component for catalysis. Moreover, the mitochondrial enzyme turns out to be an unexpected type of patchwork enzyme, composed of a tRNA methyltransferase, a short-chain dehydrogenase/reductase-family member, and a protein of hitherto unknown functional and evolutionary origin, possibly representing the enzyme's metallonuclease moiety. Apparently, animal mitochondria lost the seemingly ubiquitous RNA world remnant after reinventing RNase P from preexisting components.

Mitochondrial respiratory chain dysfunction: Implications in neurodegeneration

“…ABAD converts estrone to estradiol, a key antioxidant compound for neurone survival whose intracellular levels are decreased due to the interaction between Aβ and ABAD, a phenomenon that may contribute to Aβ-induced toxicity (Yang et al 2007;Lim et al, 2011). In addition, ABAD is a component of the mitochondrial RNAse P involved in the processing of immature mitochondrial tRNAs (Holzmann et al, 2008).…”

Ribonucleases P/MRP and the Expanding Ribonucleoprotein World

“…In eukaryotic systems, it has recently been shown that a three-component protein complex from human mitochondria shows RNase P activity (90). This labile complex, whose putative catalytic protein subunit (MRPP3) is the most easily detached, is unique among mitochondrial protein complexes in that is the only one present in the mitochondrial matrix without an endosymbiotic component (91).…”

Myxococcus CsgA, Drosophila Sniffer, and human HSD10 are cardiolipin phospholipases

“…A dramatically different model for the human disease state involves HSD10 as an essential component of the RNase P complex (Holzmann et al 2008). This complex is required for 5 ′ cleavage of mitochondrial tRNAs from the polycistronic precursor transcript and contains the proteins MRPP1, MRPP2 (HSD10), and MRPP3, each of which is essential for correct processing in vitro.…”