title: Structural basis on the dityrosyl-diiron radical cluster and the functional differences of human ribonucleotide reductase small subunits hp53R2 and hRRM2.
abstract: Ribonucleotide reductase (RNR) is an enzyme for the de novo conversion of ribonucleotides to deoxyribonucleotides. The two human RNR small subunits hRRM2 and hp53R2 share 83% sequence homology but show distinct expression patterns and function. Structural analyses of the oxidized form of hRRM2 and hp53R2 indicate that both proteins contain a conserved Gln127-hp53R2/Gln165-hRRM2 close to the dinuclear iron center and the essential tyrosine residue Tyr124-hp53R2/Tyr162-hRRM2 forms hydrogen bonds with the tyrosine and iron ligands, implying a critical role for the glutamine residue in assembling the dityrosyl-diiron radical cofactor. The present work also showed that Tyr221 in hRRM2, which is replaced by Phe183 in hp53R2, forms a hydrogen bond with Tyr162 to extend the hydrogen bond network from Gln165-hRRM2. Mutagenesis and spectroscopic experiments suggested that the tyrosine-to-phenylalanine switch at Phe183-hp53R2/Tyr221-hRRM2 could lead to differences in radical generation or enzymatic activity for hp53R2 and hRRM2. This study correlates the distinct catalytic mechanisms of the small subunits hp53R2 and hRRM2 with a hydrogen-bonding network and provides novel directions for designing and developing subunit-specific therapeutic agents for human RNR enzymes.
authors.affiliation: Department of Molecular Pharmacology, City of Hope National Medical Center, Duarte, California 91010, USA.
authors.forename: Bingsen
authors.initials: B
authors.lastname: Zhou
authors.forename: Leila
authors.initials: L
authors.lastname: Su
authors.forename: Yate-Ching
authors.initials: YC
authors.lastname: Yuan
authors.forename: Frank
authors.initials: F
authors.lastname: Un
authors.forename: Norby
authors.initials: N
authors.lastname: Wang
authors.forename: Madhukar
authors.initials: M
authors.lastname: Patel
authors.forename: Bixin
authors.initials: B
authors.lastname: Xi
authors.forename: Shuya
authors.initials: S
authors.lastname: Hu
authors.forename: Yun
authors.initials: Y
authors.lastname: Yen
mesh_terms: D000595:Amino Acid Sequence; D019943:Amino Acid Substitution / Q000235:genetics; D018797:Cell Cycle Proteins / Q000737:chemistry* / Q000378:metabolism*; D002942:Circular Dichroism; D004578:Electron Spin Resonance Spectroscopy; D005609:Free Radicals / Q000378:metabolism*; D006801:Humans; D058085:Iron Compounds / Q000378:metabolism*; D008969:Molecular Sequence Data; D016296:Mutagenesis / Q000235:genetics; D050505:Mutant Proteins / Q000737:chemistry / Q000378:metabolism; D021122:Protein Subunits / Q000737:chemistry / Q000378:metabolism*; D012262:Ribonucleoside Diphosphate Reductase / Q000737:chemistry* / Q000378:metabolism*; D012264:Ribonucleotide Reductases / Q000737:chemistry* / Q000378:metabolism*; D016415:Sequence Alignment
chemical_list: D018797:Cell Cycle Proteins; D005609:Free Radicals; D058085:Iron Compounds; D050505:Mutant Proteins; D021122:Protein Subunits; C405947:RRM2B protein, human; D012264:Ribonucleotide Reductases; C093713:ribonucleotide reductase M2; D012262:Ribonucleoside Diphosphate Reductase