Structural and functional exploration of a novel family of proteins having RNase P activity – PRO-RNase P

RNase P is essential to obtain functional tRNAs. The enzyme removes the 5’ leader sequences from tRNA precursors. Until recently all the RNases P characterised were typically found to be ribonucleoproteins with an RNA molecule responsible for the catalytic activity. Hence, it was believed that RNase P was one of the very few universally conserved remnants of the prebiotic RNA world. However, this dogma was contradicted when the molecular components of the RNase P operating in human mitochondria and plant organelles were identified. It appears to be a new kind of RNase P solely composed of proteins. These proteins that we call PRORP, i.e. “Proteinaceous RNase P” are widespread in eukaryotes. They contain two to three pentatricopeptide repeat (PPR) motifs and a metallonuclease domain predicted to perform the actual catalytic activity of RNase P. Our results show that PRORP alone catalyse the 5’ maturation of tRNA precursors that defines RNase P activity.

The discovery and characterisation of this novel kind of proteinaceous RNase P is very recent. Thus, the proposed research aims at getting a much deeper insight into the functions and mode of action of the new proteinaceous RNase P. This research will be multidisciplinary. Through complementary approaches we aim at understanding how PRORP proteins function in general. In particular, we will identify all the RNA substrates and protein partners of PRORP proteins in vivo and we will determine the 3D picture of PRORP proteins, alone and /or in complex with their precursor tRNA substrates. This will enable to compare PRORP enzymes with ribonucleoprotein RNase P and will reveal e.g. if PROPR have evolved to mimic the bacterial ribonucleoprotein RNase P. Altogether, the expected results will enable to apprehend the diversity of function that PRORP proteins can carry out in a single cell and how these functions are integrated with other cellular processes. It will indicate how PRORP proteins select their substrates, how sequences and structures influence recognition and how the actual endonucleolytic cleavage of RNA is catalysed by PRORP. Beyond the intrinsic interest in understanding fundamental biological processes, the structure-function study of PRORP proteins will help to understand the mode of action of PPR proteins. This will be relevant for a huge number of possible applications, e.g. of both agronomical and therapeutical interest.