Figure 1. The A-loop of the ErbB2 kinase domain adopts a different conformation from that of epidermal growth factor receptor (EGFR or ErbB1). A) Sequence alignment of the A-loops of EGFR and ErbB2. Identical residues are indicated with a vertical bar, similarity by a dot. Asterisks indicate the phosphorylated tyrosine residues. B) Superimposition of the modeled structures of the ErbB2 kinase domain with the A-loop in phosphorylated or unphosphorylated states. Red denotes the unphosphorylated and blue denotes the phosphorylated A-loop.