title: An RNA-binding respiratory component mediates import of type II tRNAs into Leishmania mitochondria.
abstract: Transport of tRNAs across the inner mitochondrial membrane of the kinetoplastid protozoon Leishmania requires interactions with specific binding proteins (receptors) in a multi-subunit complex. The allosteric model of import regulation proposes cooperative and antagonistic interactions between two or more receptors with binding specificities for distinct tRNA families (types I and II, respectively). To identify the type II receptor, the gene encoding RIC8A, a subunit of the complex, was cloned. The C-terminal region of RIC8A is homologous to subunit 6b of ubiquinol cytochrome c reductase (respiratory complex III), while the N-terminal region has intrinsic affinity for type II, but not for type I, tRNAs. RIC8A is shared by the import complex and complex III, indicating its bi-functionality, but is assembled differently in the two complexes. Knockdown of RIC8A in Leishmania lowered the mitochondrial content of type II tRNAs but raised that of type I tRNAs, with downstream effects on mitochondrial translation and respiration, and cell death. In RIC8A knockdown cells, a subcomplex was formed that interacted with type I tRNA, but the negative regulation by type II tRNA was lost. Mitochondrial extracts from these cells were defective for type II, but not type I, import; import and regulation were restored by purified RIC8A. These results provide evidence for the relevance of allosteric regulation in vivo and indicate that acquisition of new tRNA-binding domains by ancient respiratory components have played a key role in the evolution of mitochondrial tRNA import.
authors.affiliation: Genetic Engineering Laboratory, Indian Institute of Chemical Biology, Calcutta 700032, India.
authors.forename: Saibal
authors.initials: S
authors.lastname: Chatterjee
authors.forename: Pratik
authors.initials: P
authors.lastname: Home
authors.forename: Saikat
authors.initials: S
authors.lastname: Mukherjee
authors.forename: Bidesh
authors.initials: B
authors.lastname: Mahata
authors.forename: Srikanta
authors.initials: S
authors.lastname: Goswami
authors.forename: Gunjan
authors.initials: G
authors.lastname: Dhar
authors.forename: Samit
authors.initials: S
authors.lastname: Adhya
mesh_terms: D000495:Allosteric Site; D000818:Animals; D001692:Biological Transport; D003001:Cloning, Molecular; D003432:Cross-Linking Reagents / Q000494:pharmacology; D005786:Gene Expression Regulation; D020662:Guanine Nucleotide Exchange Factors / Q000737:chemistry* / Q000502:physiology; D006801:Humans; D007895:Leishmania tropica / Q000378:metabolism*; D026901:Membrane Transport Proteins / Q000737:chemistry* / Q000502:physiology; D008928:Mitochondria / Q000378:metabolism*; D008958:Models, Molecular; D017434:Protein Structure, Tertiary; D012313:RNA / Q000378:metabolism*; D012343:RNA, Transfer / Q000737:chemistry*; D011994:Recombinant Proteins / Q000737:chemistry
chemical_list: D003432:Cross-Linking Reagents; D020662:Guanine Nucleotide Exchange Factors; D026901:Membrane Transport Proteins; D011994:Recombinant Proteins; C561938:Ric8A protein, human; D012313:RNA; D012343:RNA, Transfer