Structural domains comprising this superfamily share the structure of the N-terminal domain of IgA peptidase M64, a family of highly selective metallo-endopeptidases, in this case for IgA, the major class of immunoglobulin in human mucosal secretions. This protein is produced by Clostridium ramosum, a member of the normal flora in the human intestine which is very rarely associated with disease. It seems appropriate to suggest that this peptidases enable these bacteria to escape specific immune defence on mucosal surfaces.

The function of this domain remains unknown.