title: RNase P enzymes: divergent scaffolds for a conserved biological reaction.
abstract: Ribonuclease P (RNase P) catalyzes the maturation of the 5' end of precursor-tRNAs (pre-tRNA) and is conserved in all domains of life. However, the composition of RNase P varies from bacteria to archaea and eukarya, making RNase P one of the most diverse enzymes characterized. Most known RNase P enzymes contain a large catalytic RNA subunit that associates with one to 10 proteins. Recently, a protein-only form of RNase P was discovered in mitochondria and chloroplasts of many higher eukaryotes. This proteinaceous RNase P (PRORP) represents a new class of metallonucleases. Here we discuss our recent crystal structure of PRORP1 from Arabidopsis thaliana and speculate on the reasons for the replacement of catalytic RNA by a protein catalyst. We conclude, based on an analysis of the catalytic efficiencies of ribonucleoprotein (RNP) and PRORP enzymes, that the need for greater catalytic efficiency is most likely not the driving force behind the replacement of the RNA with a protein catalyst. The emergence of a protein-based RNase P more likely reflects the increasing complexity of the biological system, including difficulties in importation into organelles and vulnerability of organellar RNAs to cleavage.
authors.affiliation: Department of Biological Chemistry, University of Michigan, Ann Arbor, MI, USA.
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Howard
authors.forename: Xin
authors.initials: X
authors.lastname: Liu
authors.forename: Wan Hsin
authors.initials: WH
authors.lastname: Lim
authors.forename: Bradely P
authors.initials: BP
authors.lastname: Klemm
authors.forename: Carol A
authors.initials: CA
authors.lastname: Fierke
authors.forename: Markos
authors.initials: M
authors.lastname: Koutmos
authors.forename: David R
authors.initials: DR
authors.lastname: Engelke
mesh_terms: D017360:Arabidopsis / Q000201:enzymology / Q000235:genetics / Q000378:metabolism; D029681:Arabidopsis Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D020134:Catalytic Domain; D002736:Chloroplasts / Q000201:enzymology* / Q000235:genetics / Q000378:metabolism; D019143:Evolution, Molecular; D008928:Mitochondria / Q000201:enzymology* / Q000235:genetics / Q000378:metabolism; D012322:RNA Precursors / Q000737:chemistry / Q000378:metabolism; D012323:RNA Processing, Post-Transcriptional; D016337:RNA, Catalytic / Q000235:genetics / Q000378:metabolism; D012343:RNA, Transfer / Q000235:genetics / Q000378:metabolism*; D043262:Ribonuclease P / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*
chemical_list: D029681:Arabidopsis Proteins; D012322:RNA Precursors; D016337:RNA, Catalytic; D012343:RNA, Transfer; C581753:PRORP1 protein, Arabidopsis; D043262:Ribonuclease P
keywords: MRPP; PRORP; RNA world; RNase P; mitochondrial tRNA; ribozyme; tRNA processing