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DNA recognition by a beta-sheet.

DNA recognition by a beta-sheet is discussed in the light of crystal structures of the MetJ and Arc repressors. The DNA binding geometry of a beta-sheet can be understood in terms of (i) close fitting of the two surfaces and (ii) matching of residue and base positions. A beta-sheet is not entirely flat but has a curvature. A beta-sheet of the Met-Arc family faces the DNA major groove with its convex surface; the local DNA major groove is deepest at the centre. The beta-sheet follows 6 bp; every two residues face the DNA and the first and fifth residues, which are separated by 13.2 A, bind, respectively, to the third and sixth bases, which are separated by 13.5 A, on the same DNA strand.