E6-binding structures in sequence and three-dimensional space. (A) Representative amino acid sequences shown to be necessary and sufficient for binding to HPV-16 E6. Sequence comparison among several of the E6-interacting proteins including E6AP, reveals a consensus sequence, LxxϕLsh, where L indicates leucine residues, ϕ is a hydrophobic residue, h is an amino acid residue with a side-chain capable of accepting hydrogen bonds (Asp, Glu, Asn, or Gln), s represents a small amino acid residue (Gly or Ala) and xx is a dipeptide where one of the residues is Asp, Glu, Asn, or Gln. (B) Representative structure of the E6-binding motif (Be et al., 2001) shown interacting with a schematic representing the two zinc fingers of E6. Side-chain positions of the amino acid residues essential in the motif for binding E6 are indicated by spheres. Published single-amino acid mutations of E6 that disrupt binding are in square boxes whereas mutations that retain binding are circled (Liu et al., 1999a; Nomine et al., 2006; Zimmermann et al., 1999). The E6-binding motif appears to bind to a structure formed between the two zinc finger-like structures of E6.