Structural basis on the dityrosyl-diiron radical cluster and the functional differences of human ribonucleotide reductase small subunits hp53R2 and hRRM2.
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.
Zhou
Bingsen
B
Department of Molecular Pharmacology, City of Hope National Medical Center, Duarte, California 91010, USA.
Su
Leila
L
Yuan
Yate-Ching
YC
Un
Frank
F
Wang
Norby
N
Patel
Madhukar
M
Xi
Bixin
B
Hu
Shuya
S
Yen
Yun
Y
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
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