DNA recognition by beta-sheets.

The modes of DNA recognition by beta-sheets are analyzed by using the known crystal and solution three-dimensional structures of DNA-protein complexes. Close fitting of the protein surface and the DNA surface determines the binding geometry. Interaction takes place so that essentially the N-to-C direction of the beta-strands either follows or crosses the DNA groove. Upon following the major groove a two-stranded antiparallel beta-sheet dives into the groove and contacts DNA bases with its convex side facing the DNA, while upon following the minor groove, it binds around the sugar-phosphate backbones, with its opposite concave side shielding the DNA. In order for the beta-strands crossing the minor groove to interact with the DNA, the dinucleotide steps need to almost totally helically untwist and roll around major groove. The beta-sheet, on the other hand, needs to adopt a concave curvature on the binding surface in the direction that follows the DNA minor groove, and a convex surface in the direction that bridges the sugar-phosphate backbones across the groove. The result is to produce a hyperbolic paraboloidal DNA-binding surface.