Binds 2 calcium ions per subunit. Homopentamer. Pentraxin (or pentaxin) have a discoid arrangement of 5 non-covalently bound subunits (By similarity). Expression is restricted to small intestine, stomach and colon. Within colon, expressed in epithelial cells located within the lower to mid region of transverse and distal crypts, but not in proximal colon. Strongly down-regulated in colon by dietary heme, or by dietary depletion of vitamin E. Up-regulated by calcium. Belongs to the pentraxin family.