Helix-turn-helix

This is lac repressor, a DNA binding protein. It contacts the DNA operator sequence primarily by a helix-turn-helix motif. The protein starts colored cyan and the DNA is colored light purple. The structural motif is colored helix (blue), turn (yellow) and helix (red). The blue helix fits in the major groove. The loop also contacts DNA. The red helix packs against the blue helix and the turn.

Daber, R., Stayrook, S., Rosenberg, A., Lewis, M.

Structural analysis of lac repressor bound to allosteric effectors

(2007) J.Mol.Biol. 370: 609-619(PubMed)

2pe5 (PDB)