Divergent ß-hairpins determine double-strand versus single-strand substrate recognition of human AlkB-homologues 2 and 3.
Human AlkB homologues ABH2 and ABH3 repair 1-methyladenine and 3-methylcytosine in DNA/RNA by oxidative demethylation. The enzymes have similar overall folds and active sites, but are functionally divergent. ABH2 efficiently demethylates both single- and double-stranded (ds) DNA, whereas ABH3 has a strong preference for single-stranded DNA and RNA. We find that divergent F1 β-hairpins in proximity of the active sites of ABH2 and ABH3 are central for substrate specificities. Swapping F1 hairpins between the enzymes resulted in hybrid proteins resembling the donor proteins. Surprisingly, mutation of the intercalating residue F102 had little effect on activity, while the double mutant V101A/F102A was catalytically impaired. These residues form part of an important hydrophobic network only present in ABH2. In this functionally important network, F124 stacks with the flipped out base while L157 apparently functions as a buffer stop to position the lesion in the catalytic pocket for repair. F1 in ABH3 contains charged and polar residues preventing use of dsDNA substrate. Thus, E123 in ABH3 corresponds to F102 in ABH2 and the E123F-variant gained capacity to repair dsDNA with no loss in single strand repair capacity. In conclusion, divergent sequences outside of the active site determine substrate specificities of ABH2 and ABH3.
Department of Cancer Research and Molecular Medicine, Faculty of Medicine, Norwegian University of Science and Technology, N-7489 Trondheim, Norway.
Vivi Talstad
VT
Monsen
Ottar
O
Sundheim
Per Arne
PA
Aas
Marianne P
MP
Westbye
Mirta M L
MM
Sousa
Geir
G
Slupphaug
Hans E
HE
Krokan
D000071499:AlkB Homolog 2, Alpha-Ketoglutarate-Dependent Dioxygenase; D000071500:AlkB Homolog 3, Alpha-Ketoglutarate-Dependent Dioxygenase; D020134:Catalytic Domain; D004247:DNA / Q000737:chemistry / Q000378:metabolism*; D045643:DNA Repair Enzymes / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D004277:DNA, Single-Stranded / Q000737:chemistry / Q000378:metabolism*; D049308:Dioxygenases / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D006801:Humans; D057927:Hydrophobic and Hydrophilic Interactions; D008958:Models, Molecular; D016297:Mutagenesis, Site-Directed; D017433:Protein Structure, Secondary; D013379:Substrate Specificity
D004277:DNA, Single-Stranded; D004247:DNA; D049308:Dioxygenases; C486439:ALKBH3 protein, human; D000071500:AlkB Homolog 3, Alpha-Ketoglutarate-Dependent Dioxygenase; C486440:ALKBH2 protein, human; D000071499:AlkB Homolog 2, Alpha-Ketoglutarate-Dependent Dioxygenase; D045643:DNA Repair Enzymes