LOCALIZATION OF G-PROTEINS IN MACROPHAGES AND ESCHERICHIA-COLI DURINGPHAGOCYTOSIS

Heterotrimeric GTP-binding proteins (G-proteins) have been shown to pl ay an important role in cellular signalling. However, G-protein involv ement in the intracellular spreading of bacterial pathogens is still p oorely understood. In this study, antibodies, that recognize G-protein alpha-subunits (anti-G(alpha)), were used to investigate the localiza tion of G-proteins in the macrophage-like cell line P388D(1) and E. co li, also in their L-forms, during phagocytosis. In E. coli, anti-G(alp ha)-binding sites were detected preferably in the cell wall and septa of the whole bacterial forms as well as in the cytoplasm of L-forms. W estern blotting of bacterial lysates demonstrated protein bands with p ositive immunoreaction to antibodies against G(s alpha), G(i alpha), a nd G(common alpha) with a higher affinity to the antibody against G(s alpha). Immunoreaction with the anti-G(s alpha)-antibody was markedly higher in pathogenic strains of E. coli. Because of the conserved stru cture in all GTP-binding proteins which seem to derive from a single p rimordial protein involved in signal transduction mechanisms, it is re asonable to assume that some anti-G(a)-positive proteins in E. coli mi ght be related to G-proteins of higher organisms. A putative candidate for bacterial G-proteins seems to be a 36 kDa protein. Enhancement in G-protein immunostaining in the cytoplasm of macrophages around the i nternalized bacteria testifies to the involvement of G-proteins in med iation of endocytosis responses of phagocytes.