title: Mutational analysis of bacteriophage T4 RNA ligase 1. Different functional groups are required for the nucleotidyl transfer and phosphodiester bond formation steps of the ligation reaction.
abstract: T4 RNA ligase 1 (Rnl1) exemplifies an ATP-dependent RNA ligase family that includes fungal tRNA ligase (Trl1) and a putative baculovirus RNA ligase. Rnl1 acts via a covalent enzyme-AMP intermediate generated by attack of Lys-99 N zeta on the alpha phosphorus of ATP. Mutation of Lys-99 abolishes ligase activity. Here we tested the effects of alanine mutations at 19 conserved positions in Rnl1 and thereby identified 9 new residues essential for ligase activity: Arg-54, Lys-75, Phe-77, Gly-102, Lys-119, Glu-227, Gly-228, Lys-240, and Lys-242. Seven of the essential residues are located within counterparts of conserved nucleotidyltransferase motifs I (99KEDG102), Ia (118SK119), IV (227EGYVA231), and V (238HFKIK242) that comprise the active sites of DNA ligases, RNA capping enzymes, and T4 RNA ligase 2. Three other essential residues, Arg-54, Lys-75 and Phe-77, are located upstream of the AMP attachment site within a conserved domain unique to the Rnl1-like ligase family. We infer a shared evolutionary history and active site architecture in Rnl1 (a tRNA repair enzyme) and Trl1 (a tRNA splicing enzyme). We determined structure-activity relationships via conservative substitutions and examined mutational effects on the isolated steps of Rnl1 adenylylation (step 1) and phosphodiester bond formation (step 3). Lys-75, Lys-240, and Lys-242 were found to be essential for step 1 and overall ligation of 5'-phosphorylated RNA but not for phosphodiester bond formation. These results suggest that the composition of the Rnl1 active site is different during steps 1 and 3. Mutations at Arg-54 and Lys-119 abolished the overall RNA ligation reaction without affecting steps 1 and 3. Arg-54 and Lys-119 are thereby implicated as specific catalysts of the RNA adenylation reaction (step 2) of the ligation pathway.
authors.affiliation: Molecular Biology Program, Sloan-Kettering Institute, New York, New York 10021, USA.
authors.forename: Li Kai
authors.initials: LK
authors.lastname: Wang
authors.forename: C Kiong
authors.initials: CK
authors.lastname: Ho
authors.forename: Yi
authors.initials: Y
authors.lastname: Pei
authors.forename: Stewart
authors.initials: S
authors.lastname: Shuman
mesh_terms: D000409:Alanine / Q000737:chemistry; D020816:Amino Acid Motifs; D000595:Amino Acid Sequence; D001120:Arginine / Q000737:chemistry; D017122:Bacteriophage T4 / Q000201:enzymology*; D001665:Binding Sites; D004252:DNA Mutational Analysis; D004587:Electrophoresis, Agar Gel; D008239:Lysine / Q000737:chemistry; D008969:Molecular Sequence Data; D009154:Mutation; D010649:Phenylalanine / Q000737:chemistry; D017434:Protein Structure, Tertiary; D012313:RNA / Q000378:metabolism; D011130:RNA Ligase (ATP) / Q000737:chemistry* / Q000235:genetics*; D012343:RNA, Transfer / Q000378:metabolism; D017386:Sequence Homology, Amino Acid; D013329:Structure-Activity Relationship; D014764:Viral Proteins
chemical_list: D014764:Viral Proteins; D010649:Phenylalanine; D012313:RNA; D012343:RNA, Transfer; D001120:Arginine; D011130:RNA Ligase (ATP); C477285:bacteriophage T4 RNA ligase 1; D008239:Lysine; D000409:Alanine