A Unique Mycoplasma Protein Generically Binds All Types of Antibodies and Blocks Antigen Binding

They reported in the February 7, 2014, issue of the journal Science that the crystal structure of the external domain of transmembrane Protein M differed from other known protein structures, as did its mechanism of antibody binding. Protein M bound with high affinity to all types of human and nonhuman immunoglobulin G, predominantly through attachment to the conserved portions of the variable region of the kappa and gamma light chains. Furthermore, Protein M blocked antibody-antigen binding, likely because of its large C-terminal domain extending over the antibody-combining site, blocking entry to large antigens.

The investigators suggested that the most immediate use for Protein M will likely be as a tool for immobilizing antibodies in mixtures and cell cultures as a preparatory step in the generation of highly purified antibodies for research and drug manufacturing. “It may be the most useful antibody purification device ever found,” said senior author Dr. Richard A. Lerner, professor of immunochemistry at The Scripps Research Institute.

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