Recognition of cng-repetitive rnas associated with human diseases by rna silencing suppressor p19 as studied by x-ray crystallography

Resumen

Expanded tracts of CNG-triplet repetitive sequences in human genome cause many diseases. We think that repeats cause diseases through RNA silencing pathway (RNAi) due to formation of the double helical RNAs, containing mismatches at each third position. To be recognized by RNAi machinery, such RNAs have to be structurally similar to the canonic A-RNA helix. To test if all CNG-repetitive RNAs form A-RNA double helices that can be easily recognized by an A-RNA binding protein and explore structural behavior of these double-helices upon variation of mismatches, strand-alignments and CNG-repeat regularity, multiple crystal structure determinations have been carried out. Various CNG-repetitive RNAs, designed to contain all possible mismatches Na¿Nb in double-helical structure, were studied by X-Ray crystallography in complex with RNA-silencing suppressor p19 that is known to bind RNA duplexes of a 19 base pairs length in a sequence unspecific way. Comparative structural analysis of the p19/RNA complexes elucidated the important role of the CNG-triplet repetition in the RNA sequences for the double helical structure stability. In turn, the `structural¿ adaptability of the CNG-repetitive RNAs seems more dependable on mismatch pairs. The second part of the work deals with the attempt to find and introduce mutations into p19 that would allow it to recognize one of the CNG-triplets in CNG-repetitive RNA duplex. For the first time, i) the structural behavior of various CNG-repetitive RNAs was studied upon complex-formation with an A-RNA binding protein and ii) RNA sequence specific mutations of p19 were structurally described.