A CYTOLYTIC FUNCTION FOR A SIALIC ACID-BINDING LECTIN THAT IS A MEMBER OF THE PENTRAXIN FAMILY OF PROTEINS

A variety of invertebrates possess plasma lectins with sialic acid rec ognition capabilities, One of the best studied of these lectins is lim ulin, which is a member of the pentraxin family of proteins and is fou nd in the plasma of the American horseshoe crab, Limulus polyphemus, W e find that limulin is one of several sialic acid-binding lectins of l imulus plasma and is present at a much lower abundance than Limulus C- reactive protein, the other plasma pentraxin, Limulin was purified by sequential affinity chromatography on phosphorylethanolamine agarose, which isolates the pentraxins and separates limulin from the other sia lic acid-binding lectins of the plasma, followed by fetuin-Sepharose, which binds limulin and separates it from Limulus C-reactive protein, the most abundant pentraxin of the plasma, We show here that limulin i s the mediator of the Ca+2-dependent hemolytic activity found in the p lasma of Limulus, Plasma that was depleted in the pentraxins by passag e over phosphorylethanolamine-agarose or was depleted in the sialic ac id-binding lectins by passage over fetuin Sepharose lacked hemolytic a ctivity, Purified limulin was hemolytic at concentrations of 3-5 nM. T he other sialic acid-binding lectins of Limulus plasma and Limulus C-r eactive protein were nonhemolytic. Foreign cell cytolysis by limulin r epresents a novel function for a plasma lectin and is the first docume nted function for limulin.