The solution structure of the Za domain of the human RNA editing enzyme ADAR1 reveals a prepositioned binding surface for Z-DNA
M. Schade, C. Turner, R. Kuehne, P. Schmieder, K. Lowenhaupt, A. Herbert, A. Rich, H. Oschkinat
Proc. Natl. Acad. Sci. USA (1999) 96, 12465-12470
Double-stranded RNA deaminase I (ADAR1) contains the Z-DNA binding domain Za. Here we report the solution structure of free Za and map the interaction surface with Z-DNA, confirming roles previously assigned to residues by mutagenesis. Comparison with the crystal structure of the (Za)2/Z-DNA complex shows that most Z-DNA contacting residues in free Za are prepositioned to bind Z-DNA, thus minimizing the entropic cost of binding. Comparison with homologous (a + b)helix-turn-helix/B-DNA complexes suggests that binding of Za to B-DNA is disfavored by steric hindrance, but does not eliminate the possibility that related domains may bind to both B- and Z-DNA.