Human β2-microglobulin is a substrate of tissue transglutaminase: Polymerization in solution and on the cell surface

Abstract

Incubation of purified human β2-microglobulin (B2-m) with tissue transglutaminase (Tgase) resulted in the formation of high molecular weight polymers revealed by sodium dodecyl sulfate polyacrylamide gel electrophoresis. In the presence of 30 mM [14C]methylamine, the polymer formation was prevented, but incorporation of methylamine into β2-m (equal to 1 methylamine per 1 molecule) could be observed. From the sheddings of peripheral blood mononuclear cells occurring in the presence of Tgase, it is apparent that anti-β2-m immunoadsorbent removed, in addition to human leukocyte antigen (HLA) and β2-m, some other proteins. The enzyme could incorporate [14C]methylamine into β2-m of the shedding cells. On addition of rabbit anti-human β2-m antibody, followed by fluoresceine-labeled goat anti-rabbit IgG antibody to human mononuclear blood cells, the otherwise homogeneous distribution of fluorescence turned into spots and patches on cells previously incubated with Tgase or Ca2+-ionophore A23187.