title: Structural and biochemical studies of the distinct activity profiles of Rai1 enzymes.
abstract: Recent studies showed that Rai1 and its homologs are a crucial component of the mRNA 5'-end capping quality control mechanism. They can possess RNA 5'-end pyrophosphohydrolase (PPH), decapping, and 5'-3' exonuclease (toward 5' monophosphate RNA) activities, which help to degrade mRNAs with incomplete 5'-end capping. A single active site in the enzyme supports these apparently distinct activities. However, each Rai1 protein studied so far has a unique set of activities, and the molecular basis for these differences are not known. Here, we have characterized the highly diverse activity profiles of Rai1 homologs from a collection of fungal organisms and identified a new activity for these enzymes, 5'-end triphosphonucleotide hydrolase (TPH) instead of PPH activity. Crystal structures of two of these enzymes bound to RNA oligonucleotides reveal differences in the RNA binding modes. Structure-based mutations of these enzymes, changing residues that contact the RNA but are poorly conserved, have substantial effects on their activity, providing a framework to begin to understand the molecular basis for the different activity profiles.
authors.affiliation: Department of Biological Sciences, Columbia University, New York, NY 10027, USA.
authors.forename: Vivien Ya-Fan
authors.initials: VY
authors.lastname: Wang
authors.affiliation: Department of Cell Biology and Neuroscience, Rutgers University, Piscataway, NJ 08854, USA.
authors.forename: Xinfu
authors.initials: X
authors.lastname: Jiao
authors.affiliation: Department of Cell Biology and Neuroscience, Rutgers University, Piscataway, NJ 08854, USA.
authors.forename: Megerditch
authors.initials: M
authors.lastname: Kiledjian
authors.affiliation: Department of Biological Sciences, Columbia University, New York, NY 10027, USA ltong@columbia.edu.
authors.forename: Liang
authors.initials: L
authors.lastname: Tong
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D017124:Conserved Sequence; D004722:Endoribonucleases / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D005095:Exoribonucleases / Q000737:chemistry / Q000378:metabolism; D005656:Fungal Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D006867:Hydrolases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D051379:Mice; D008958:Models, Molecular; D009154:Mutation; D009843:Oligoribonucleotides / Q000378:metabolism; D011485:Protein Binding; D011755:Pyrophosphatases / Q000737:chemistry / Q000378:metabolism; D016601:RNA-Binding Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism
chemical_list: D005656:Fungal Proteins; D009843:Oligoribonucleotides; D016601:RNA-Binding Proteins; C030052:mRNA decapping enzymes; D006867:Hydrolases; D004722:Endoribonucleases; D005095:Exoribonucleases; D011755:Pyrophosphatases