Fig. 1. Primary structure of CHL2. (A) Schematic representation of chordin, CHL1(l), and CHL2. SP stands for signal peptide. The CR1 and CR3 regions in CHL1 and CHL2 (black boxes) are most homologous to CR3 of chordin (also in black). The chordin CR1 (in gray) and CR3 possess the BMP-binding capability (Larrain et al., 2000). Putative BMP1/Tolloid cleavage sites are indicated with an asterisk, while actual Tolloid cleavage sites (Scott et al., 1999) are shown by vertical arrows. The CHL1 ORF had two sites with amino acid sequence variations (dE and d5) (Nakayama et al., 2001). (B) Amino acid sequences of mouse, rat and human CHL2 protein precursors. The three CRs are indicated by boxes. The vertical arrow indicates the NH₂-terminal amino acid of mature mCHL2-FLAG (Leu²⁶), as determined by amino acid sequencing of purified recombinant protein. (C) Amino acid sequence alignment showing sequence similarities between CR1 or CR3 of mouse CHL1 and CHL2, and CR3 of mouse chordin. Ten conserved cysteines (highlighted in black) are found in the spacing typical of vertebrate chordins. Other conserved amino acids are highlighted in gray.