Characterization of a lectin in human plasma analogous to bovine conglutinin

The structural characteristics of a human plasma protein analogous to bovine conglutinin were studied. The protein was previously found to bind to complement-reacted IgG in a calcium-dependent and N-acetyl-D-glucosamine-inhibitable manner and it further shows cross-reactivity with anti-bovine conglutinin antibody. By gel permeation chromatography the conglutinin activity in human plasma was localized to fractions containing proteins of Mr at around 700,000. The conglutinin was localized by one ELISA for antigen determinants and by another for biological activity. When analysed by sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE) under non-reducing conditions these fractions were shown to contain proteins of about 300,000. When human conglutinin-like protein, partially purified by affinity chromatography, was analysed unreduced by SDS-PAGE followed by western blotting, the cross-reacting anti-bovine conglutinin antibody bound to a protein with an Mr of 330,000. When the sample was reduced and alkylated before electrophoresis a band of 66,000 was immunostained. The 330,000 and 66,000 proteins were shown to be collagenase sensitive. 125I-iC3b was seen to bind to the 330,000 band when incubated with western blots of partially purified human conglutinin.