Structural and functional analyses of the severe acute respiratory syndrome coronavirus endoribonuclease Nsp15.
The severe acute respiratory syndrome (SARS) coronavirus encodes several RNA-processing enzymes that are unusual for RNA viruses, including Nsp15 (nonstructural protein 15), a hexameric endoribonuclease that preferentially cleaves 3' of uridines. We solved the structure of a catalytically inactive mutant version of Nsp15, which was crystallized as a hexamer. The structure contains unreported flexibility in the active site of each subunit. Substitutions in the active site residues serine 293 and proline 343 allowed Nsp15 to cleave at cytidylate, whereas mutation of leucine 345 rendered Nsp15 able to cleave at purines as well as pyrimidines. Mutations that targeted the residues involved in subunit interactions generally resulted in the formation of catalytically inactive monomers. The RNA-binding residues were mapped by a method linking reversible cross-linking, RNA affinity purification, and peptide fingerprinting. Alanine substitution of several residues in the RNA-contacting portion of Nsp15 did not affect hexamer formation but decreased the affinity of RNA binding and reduced endonuclease activity. This suggests a model for Nsp15 hexamer interaction with RNA.
Department of Biochemistry and Biophysics, Texas A & M University, College Station, Texas 77843-2128.
Kanchan
K
Bhardwaj
Department of Biochemistry and Biophysics, Texas A & M University, College Station, Texas 77843-2128.
Satheesh
S
Palaninathan
Department of Biochemistry and Biophysics, Texas A & M University, College Station, Texas 77843-2128.
Joanna Maria Ortiz
JMO
Alcantara
Department of Biochemistry and Biophysics, Texas A & M University, College Station, Texas 77843-2128; Department of Entomology, Texas A & M University, College Station, Texas 77843-2128.
Lillian
L
Li Yi
Department of Biochemistry and Biophysics, Texas A & M University, College Station, Texas 77843-2128; Department of Entomology, Texas A & M University, College Station, Texas 77843-2128.
Linda
L
Guarino
Department of Biochemistry and Biophysics, Texas A & M University, College Station, Texas 77843-2128.
James C
JC
Sacchettini
Department of Biochemistry and Biophysics, Texas A & M University, College Station, Texas 77843-2128. Electronic address: ckao@tamu.edu.
C Cheng
CC
Kao
D000595:Amino Acid Sequence; D001665:Binding Sites; D002384:Catalysis; D018360:Crystallography, X-Ray / Q000379:methods; D004722:Endoribonucleases; D007930:Leucine / Q000737:chemistry; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009154:Mutation; D011485:Protein Binding; D011487:Protein Conformation; D011743:Pyrimidines / Q000737:chemistry; D012324:RNA-Dependent RNA Polymerase / Q000737:chemistry* / Q000502:physiology; D045473:Severe acute respiratory syndrome-related coronavirus / Q000378:metabolism*; D012694:Serine / Q000737:chemistry; D013379:Substrate Specificity; D017361:Viral Nonstructural Proteins / Q000737:chemistry* / Q000502:physiology
D011743:Pyrimidines; D017361:Viral Nonstructural Proteins; D012694:Serine; D012324:RNA-Dependent RNA Polymerase; D004722:Endoribonucleases; C000657925:nidoviral uridylate-specific endoribonuclease; D007930:Leucine