CRYSTAL-STRUCTURE OF AN ENGRAILED HOMEODOMAIN-DNA COMPLEX AT 2.8-A RESOLUTION - A FRAMEWORK FOR UNDERSTANDING HOMEODOMAIN-DNA INTERACTIONS

The crystal structure of a complex containing the engrailed homeodomain and a duplex DNA site has been determined at 2.8 Å resolution and refined to a crystallographic R factor of 24.4%. In this complex, two separate regions of the 61 amino acid polypeptide contact a TAAT subsite. An N-terminal arm fits into the minor groove, and the side chains of Arg-3 and Arg-5 make contacts near the 5′ end of this "core consensus" binding site. An α helix fits into the major groove, and the side chains of Ile-47 and Asn-51 contact base pairs near the 3′ end of the TAAT site. This "recognition helix" is part of a structurally conserved helix-turn-helix unit, but these helices are longer than the corresponding helices in the λ repressor, and the relationship between the helix-turn-helix unit and the DNA is significantly different. © 1990.