| Structural highlights
Function
[ALKB8_HUMAN] Catalyzes the methylation of 5-carboxymethyl uridine to 5-methylcarboxymethyl uridine at the wobble position of the anticodon loop in tRNA. Catalyzes the last step in the formation of 5-methylcarboxymethyl uridine at the wobble position of the anticodon loop in target tRNA. Has a preference for tRNA(Arg) and tRNA(Glu), and does not bind tRNA(Lys). Required for normal survival after DNA damage. May inhibit apoptosis and promote cell survival and angiogenesis.[1] [2]
Publication Abstract from PubMed
Humans express nine paralogs of the bacterial DNA repair enzyme AlkB, an iron/2-oxoglutarate-dependent dioxygenase that reverses alkylation damage to nucleobases. The biochemical and physiological roles of these paralogs remain largely uncharacterized, hampering insight into the evolutionary expansion of the AlkB family. However, AlkB homolog 8 (ABH8), which contains RNA recognition motif (RRM) and methyltransferase domains flanking its AlkB domain, recently was demonstrated to hypermodify the anticodon loops in some tRNAs. To deepen understanding of this activity, we performed physiological and biophysical studies of ABH8. Using GFP fusions, we demonstrate that expression of the Caenorhabditis elegans ABH8 ortholog is widespread in larvae but restricted to a small number of neurons in adults, suggesting that its function becomes more specialized during development. In vitro RNA binding studies on several human ABH8 constructs indicate that binding affinity is enhanced by a basic alpha-helix at the N terminus of the RRM domain. The 3.0-A-resolution crystal structure of a construct comprising the RRM and AlkB domains shows disordered loops flanking the active site in the AlkB domain and a unique structural Zn(II)-binding site at its C terminus. Although the catalytic iron center is exposed to solvent, the 2-oxoglutarate co-substrate likely adopts an inactive conformation in the absence of tRNA substrate, which probably inhibits uncoupled free radical generation. A conformational change in the active site coupled to a disorder-to-order transition in the flanking protein segments likely controls ABH8 catalytic activity and tRNA binding specificity. These results provide insight into the functional and structural adaptations underlying evolutionary diversification of AlkB domains.
Crystal structure and RNA binding properties of the RNA recognition motif (RRM) and AlkB domains in human AlkB homolog 8 (ABH8), an enzyme catalyzing tRNA hypermodification.,Pastore C, Topalidou I, Forouhar F, Yan AC, Levy M, Hunt JF J Biol Chem. 2012 Jan 13;287(3):2130-43. Epub 2011 Nov 7. PMID:22065580[3]
From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.
References
- ↑ Shimada K, Nakamura M, Anai S, De Velasco M, Tanaka M, Tsujikawa K, Ouji Y, Konishi N. A novel human AlkB homologue, ALKBH8, contributes to human bladder cancer progression. Cancer Res. 2009 Apr 1;69(7):3157-64. doi: 10.1158/0008-5472.CAN-08-3530. Epub, 2009 Mar 17. PMID:19293182 doi:http://dx.doi.org/10.1158/0008-5472.CAN-08-3530
- ↑ Fu D, Brophy JA, Chan CT, Atmore KA, Begley U, Paules RS, Dedon PC, Begley TJ, Samson LD. Human AlkB homolog ABH8 Is a tRNA methyltransferase required for wobble uridine modification and DNA damage survival. Mol Cell Biol. 2010 May;30(10):2449-59. doi: 10.1128/MCB.01604-09. Epub 2010 Mar , 22. PMID:20308323 doi:http://dx.doi.org/10.1128/MCB.01604-09
- ↑ Pastore C, Topalidou I, Forouhar F, Yan AC, Levy M, Hunt JF. Crystal structure and RNA binding properties of the RNA recognition motif (RRM) and AlkB domains in human AlkB homolog 8 (ABH8), an enzyme catalyzing tRNA hypermodification. J Biol Chem. 2012 Jan 13;287(3):2130-43. Epub 2011 Nov 7. PMID:22065580 doi:http://dx.doi.org/10.1074/jbc.M111.286187
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