Structures of the T. brucei kRNA editing factorMRB1590 reveal unique RNA-binding pore motifcontained within an ABC-ATPase fold

Kinetoplastid RNA (kRNA) editing is a process thatcreates translatable mitochondrial mRNA transcriptsfrom cryptogene encoded RNAs and is unique forkinetoplastids, such as Trypanosoma brucei. In additionto the catalytic 20S editosome, multiple accessoryproteins are required for this conversion. Recently, the multiprotein mitochondrial RNA bindingcomplex 1 (MRB1) has emerged as a key player inthis process. MRB1 consists of six core proteins butmakes dynamic interactions with additional accessoryproteins. Here we describe the characterizationof one such factor, the 72 kDa MRB1590 protein. Invivo experiments indicate a role for MRB1590 in editingmitochondrial mRNA transcripts, in particular thetranscript encoding the ATP synthase subunit 6 (A6) .Structural studies show that MRB1590 is dimericand contains a central ABC-ATPase fold embeddedbetween novel N- and C-terminal regions. The Nterminaldomains combine to create a basic pore andbiochemical studies indicate residues in this regionparticipate in RNA binding. Structures capturing distinctMRB1590 conformations reveal that the RNAbinding pore adopts closed and open states, withthe latter able to accommodate RNA. Based on thesefindings, implications for MRB1590 function are discussed.