This is the Cys-box (cysteine-rich) domain found on the N-terminal of anosmin-1 proteins. It is suggested that the Cys-box domain may resemble the cysteine-rich region of the insulin-like growth factor receptor [1]. Family members are found in chordates.

1: Extended and flexible domain solution structure of the extracellular matrix protein anosmin-1 by X-ray scattering, analytical ultracentrifugation and constrained modelling. Hu Y, Sun Z, Eaton JT, Bouloux PM, Perkins SJ; J Mol Biol. 2005;350:553-570. PMID:15949815