Protein M

Protein M is an immunoglobulin-binding protein found on the cell surface of the human pathogenic bacterium Mycoplasma genitalium. It is presumably a universal antibody-binding protein, as it is known to be reactive against all antibody types tested so far. It is capable of preventing the antigen-antibody interaction due to its high binding affinity to any antibody. The Scripps Research Institute announced its discovery in 2014. It was detected from the bacterium while investigating its role in patients suffering from a cancer, multiple myeloma.

Mycoplasma genitalium was discovered in 1980 from two male patients suffering from non-gonococcal urethritis at St Mary's Hospital, Paddington, London. After two years, in 1983, it was identified as a new species. After several years of intense research, it was found to be the cause of sexually transmitted diseases, such as urethritis (inflammation of the urinary tract) both in men and women, and also cervicitis (inflammation of cervix) and pelvic inflammation in women. However, the molecular nature of its pathogenicity remained unknown for three decades.

On 6 February 2014, The Scripps Research Institute announced the discovery of a novel protein, which they named Protein M, from the M. genitalium cell membrane. Scientists identified the protein during investigations on the origin of multiple myeloma, a type of B-cell carcinoma. To understand the long-term M. genitalium infection, Rajesh Grover, a senior staff scientist in the Lerner laboratory, tested antibodies from the blood samples of patients with multiple myeloma against different Mycoplasma species. He found that M. genitalium was particularly responsive to all types of antibodies he tested from 20 patients. The antibody reactivity was found to be due to an undiscovered protein that is chemically responsive to all types of human and non-human antibodies available. When they isolated and analysed the protein, they discovered that it was unique both in structure and biological functions. Its structure has no resemblance to any known protein listed in the Protein Data Bank.

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