Protein A is a cell wall component of Staphylococcus aureus. It consists of a single polypeptide chain shaped as a cylinder, which contains five antibody–binding domains. These high affinity regions are specifically bonded to Fc region of the immunoglobulins (specially IgGs of different species). Protein A is temperature stable and it retains its native conformation even in the presence of denaturing agents. Protein A resins have been widely used to purify a wide range of immunoglobulins of different mammalian species and also to purify certain IgG subclasses that have no affinity.
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