The function of this domain is unknown, but it is found towards the N-terminus of bacterial proteins carrying the CAP domain, Pfam:PF00188. All members that do not otherwise carry an additional Cu_amine_oxidN1, Pfam:PF07833, domain are likely to be extracellular as they start with a signal-peptide. Most other non-bacterial proteins with the CAP domain are allergenic [1].

1: Characteristic motifs for families of allergenic proteins. Ivanciuc O, Garcia T, Torres M, Schein CH, Braun W; Mol Immunol. 2009;46:559-568. PMID:18951633