Table 2.

Conserved aromatic-amine interaction and indole–hydrogen bonds in known lipocalin structures

3D Structures	Aromatic-amine interaction	Hydrogen bond (atom)
Retinol-binding protein (current)	Try24–Arg139	Trp24 (NE1)–Phe20 (O)
β-Lactoglobulin	Trp19–Arg124	Trp19 (NE1)–Val15 (O)
Bilin-binding protein	Trp27–Arg137	Trp27 (NE1)–His24 (O)
Major urinary protein	Trp23–Arg126	Trp23 (NE1)–Ile19 (O)
Odorant-binding protein	Trp17–Lys121	Trp17 (NE1)–Leu13 (O)
Androgen-dependent epididymal retinoic acid–binding protein	Trp15–Arg119	Trp15 (NE1)–Phe11 (O)
Allergen Bos D2	Trp16–Lys119	Trp16 (NE1)–Ile12 (O)
Triabin	Trp25–Arg129	Trp25 (NE1)–Phe20 (O)