Crystal structure of a heterodimer of editosome interaction proteins in complex with two copies of a cross-reacting nanobody.
The parasite Trypanosoma brucei, the causative agent of sleeping sickness across sub-Saharan Africa, depends on a remarkable U-insertion/deletion RNA editing process in its mitochondrion. A approximately 20 S multi-protein complex, called the editosome, is an essential machinery for editing pre-mRNA molecules encoding the majority of mitochondrial proteins. Editosomes contain a common core of twelve proteins where six OB-fold interaction proteins, called A1-A6, play a crucial role. Here, we report the structure of two single-strand nucleic acid-binding OB-folds from interaction proteins A3 and A6 that surprisingly, form a heterodimer. Crystal growth required the assistance of an anti-A3 nanobody as a crystallization chaperone. Unexpectedly, this anti-A3 nanobody binds to both A3(OB) and A6, despite only ~40% amino acid sequence identity between the OB-folds of A3 and A6. The A3(OB)-A6 heterodimer buries 35% more surface area than the A6 homodimer. This is attributed mainly to the presence of a conserved Pro-rich loop in A3(OB). The implications of the A3(OB)-A6 heterodimer, and of a dimer of heterodimers observed in the crystals, for the architecture of the editosome are profound, resulting in a proposal of a 'five OB-fold center' in the core of the editosome.
Department of Biochemistry, Biomolecular Structure Center, School of Medicine, University of Washington, PO Box 357742, Seattle WA 98195, USA.
Young-Jun
YJ
Park
Els
E
Pardon
Meiting
M
Wu
Jan
J
Steyaert
Wim G J
WG
Hol
D000595:Amino Acid Sequence; D003429:Cross Reactions; D018360:Crystallography, X-Ray; D019281:Dimerization; D024101:Mitochondrial Proteins / Q000737:chemistry* / Q000276:immunology; D008958:Models, Molecular; D008969:Molecular Sequence Data; D055503:Protein Multimerization; D017434:Protein Structure, Tertiary; D015800:Protozoan Proteins / Q000737:chemistry* / Q000276:immunology; D017393:RNA Editing; D016601:RNA-Binding Proteins / Q000737:chemistry* / Q000276:immunology; D057127:Single-Chain Antibodies / Q000737:chemistry* / Q000276:immunology
D024101:Mitochondrial Proteins; D015800:Protozoan Proteins; D016601:RNA-Binding Proteins; D057127:Single-Chain Antibodies