Nurse shark IgNAR (gray tubes) bound to hen egg white lysozyme (solid surface over blue tubes). The complementarity determining region (CDR) loops CDR1 (green) and CDR3 (yellow) of IgNAR are used for lysozyme recognition. Two other regions of sequence hypervariability HV2 (purple) and HV4 (cyan) are also highlighted and may be used for antigen recognitin in other IgNAR molecules.