Newborn IgM and IgW VH families conserve residues important for the Ig fold motif. The VH structures are formatted per the IMGT numbering system . (A) IgM Ig fold is maintained in IgM VH family members. The nurse shark canonical IgM Genbank accession # M92851  was compared to the more divergent members from group I clone 30E and group VI clone 36E. Hydrophobic amino acids (hydropathy index with positive value: I, V, L, F, C, M, A) and tryptophan (W) at positions at which more than 50 % of analysed IG and TR sequences were positive are highlighted in blue . Prolines (P) are marked in yellow and conserved Ig fold residues Cys at positions 23 and 104, and Tryp (W) at position 41 are highlighted in yellow lettering. This modeling demonstrates that Ig fold motifs strand B and F Cys and hydrophobic core residues are conserved in these VH domains. Hatched circles represent residues of the canonical VH IMGT structure that are not utilized in the shark VH. (B) The IMGT numbering system was used to compare the VH domains of the conventional IgW U51450  to representatives of the IgW VH divergent groups III and V. These divergent VH families maintain the Ig fold motif and utilize Pro in the FR similar to IgM (refer to part A).