Spears J.L.,Ohio State Center for Biology |
Rubio M.A.T.,Ohio State Center for Biology |
Gaston K.W.,Ohio State Center for Biology |
Wywial E.,International Institute of Molecular and Cell Biology in Warsaw |
And 6 more authors.
Journal of Biological Chemistry | Year: 2011
Editing of adenosine (A) to inosine (I) at the first anticodon position in tRNA is catalyzed by adenosine deaminases acting on tRNA (ADATs). This essential reaction in bacteria and eukarya permits a single tRNA to decode multiple codons. Bacterial ADATa is a homodimer with two bound essential Zn2+. The ADATa crystal structure revealed residues important for substrate binding and catalysis; however, such high resolution structural information is not available for eukaryotic tRNA deaminases. Despite significant sequence similarity among deaminases, we continue to uncover unexpected functional differences between Trypanosoma brucei ADAT2/3 (TbADAT2/3) and its bacterial counterpart. Previously, we demonstrated that TbADAT2/3 is unique in catalyzing two different deamination reactions. Here we show by kinetic analyses and inductively coupled plasma emission spectrometry that wild type TbADAT2/3 coordinates two Zn2+ per heterodimer, but unlike any other tRNA deaminase, mutation of one of the key Zn2+-coordinating cysteines in TbADAT2 yields a functional enzyme with a single-bound zinc. These data suggest that, at least, TbADAT3 may play a role in catalysis via direct coordination of the catalytic Zn2+. These observations raise the possibility of an unusual Zn2+ coordination interface with important implications for the function and evolution of editing deaminases. © 2011 by The American Society for Biochemistry and Molecular Biology, Inc.