Sodium dodecyl sulphate-polyacrylamide gel electrophoresis and western blotting for protein antigen analysis

Sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE) has now become a standard tool in most laboratories for protein analysis and purification. Several SDS-PAGE systems have been described but the most widely used one is the discontinuous buffer system introduced for disc gel electrophoresis. Western blotting or the process of transfer of the electrophoretically separated proteins onto immobilizing matrices such as nitrocellulose membrane is an extension of SDS-PAGE system and provides, on the nitrocellulose blot, an identical copy of the electrophoretic separation pattern of the proteins present in the gels. The immobilized proteins can be further reacted with an appropriate probe such as antibody for identification of its corresponding antigen. The protein antigen/antibody complex is then detected by using radioactively labelled or enzyme-linked second antibody probe. The technique is very useful for analysis and characterization of complex protein antigens using immune sera from several sources or vice versa. The protocol given presented here illustrates such a separation by which complex protein antigens of blood stages of Plasmodium vivax obtained from blood of patients with vivax malaria are fractionated by SDS-PAGE and treated with immune sera from patients with acute vivax malaria and the antigen/antibody complex formed are detected by 125I-labelled anti-human immunoglobulins. 5 refs, 2 figs