Distinct substrate specificities of the human tRNA methyltransferases TRMT10A and TRMT10B

Binding affinity does not determine substrate specificity patterns for hTRMT10A and hTRMT10B. Affinities of hTRMT10A and hTRMT10B were determined for each of four different human tRNAs using a double-filter binding assay. The four tRNAs were chosen to represent two G₉-containing tRNA (Arg and Trp, modified efficiently by hTRMT10A and much less efficiently by hTRMT10B), and two A₉-containing tRNAs (Asp and Ala, with Asp modified only by hTRMT10B, and Ala modified by neither enzyme). Apparent K_D values determined by the fit of the data from the binding assay, as described in Materials and Methods, are plotted for each enzyme. Measured K_D,app for hTRMT10A: 0.65 µM (Arg), 2.7 µM (Trp), 2.2 µM (Asp), and 2.2 µM (Ala), and for hTRMT10B: 1.3 µM (Arg), 3.0 µM (Trp), 3.8 µM (Asp), and 2.2 µM (Ala). Error bars represent standard error derived from two independent assays.