Evolutionary conundrum of RNase P: from a catalytic RNA form to a protein only enzyme form

Abstract

RNaza P je esencijalna endonukleaza koja katalizira procesiranje 5'-vodećeg slijeda pre-tRNA. Postoje dva tipa RNaze P: RNA-ovisni enzim tj ribonukleoprotein te isključivo proteinska RNaza P (PRORP). Oba oblika koriste sličan mehanizam katalize i prepoznavanja supstrata te je nedavno otkriveno da isključivo proteinski oblik postoji u svim domenama života, a ne samo kod eukariota, što je dovelo do pitanja zašto su oba oblika RNaze P opstala i koji je oblik onda zapravo ancestralni. Istraživanja komponenti ribonukleoproteinskog oblika RNaze P otkrila su da osim što ovaj enzim ima ulogu katalize procesiranje pre-tRNA, njegove podjedinice sudjeluju u mnogim drugim biokemijskim procesima koji su bitni za normalno funkcioniranje stanice zbog čega je njegov opstanak u stanici esencijalan. RNP oblici RNaze P u svim domenama života imaju visoko očuvano aktivno mjesto katalize, za razliku od PRORP oblika koji ne dijele nikakvu sličnost. Ove činjenice ukazuju na to da je RNP oblik ancestralni, a da su PRORP oblici kasnije neovisno konvergentno evoluirali. Evolucijska priča RNaze P veoma je kompleksna i postoje mnoga nagađanja kako se odvijala, no pravi odgovor još uvijek ostaje enigmaRNase P is an essential endonuclease responsible for catalyzing 5’ end maturation of pre-tRNAs. Two types of RNase P enzymes exist: RNA-dependent enzymes (ribonucleoproteins) and protein-only RNase Ps (PRORP). A recent discovery that both types of RNase P exist in all domains of life and that both types use a similar mechanism for catalysis and substrate recognition, inspires questions relating to the ancestral form of RNase P as well as to the reasoning for retention of both types in contemporary organisms. The protein components of RNA-dependent enzymes are not only involved in the catalyzes of 5' end maturation but they also play an important role in various biochemical processes in the cell. This may provide a plausible explanation why the retention of these proteins is essential. The active site of the RNA-dependent type of RNase P is universally conserved in all domains of life, unlike the active site of the protein only types of RNase P which greatly varies. This suggests that the RNA-dependent type of RNase P is the ancestral form and that the diverse PRORP forms convergently evolved afterwards. The evolutionary story of RNase P is very complex and there are many speculations on how RNase P evolved but the real answer is still not clear