Staphylococcus aureus Protein A (SpA) (SpA)

Staphylococcus aureus Protein A (SpA) is a 42 kDa surface protein and a major virulence factor of Staphylococcus aureus [1]. It is primarily known for its ability to bind the Fc region of immunoglobulin G (IgG) with high affinity, which effectively coats the bacterium in host antibodies in an inverted orientation, preventing recognition by phagocytic Fc receptors and inhibiting opsonophagocytosis [2]. SpA also functions as a B-cell superantigen by binding to the VH3-type B-cell receptors, triggering non-specific B-cell proliferation and subsequent depletion, which impairs the host's adaptive immune response [4]. Given its pivotal role in immune evasion, SpA is a significant target for therapeutic interventions, including monoclonal antibodies like 514G3 and toxoid vaccines like SpA-KKAA, which aim to neutralize its activity and enhance bacterial clearance [3]. Beyond its role in infection, the high affinity of SpA for IgG is exploited in biotechnology for antibody purification and in medical devices like the Prosorba column for treating autoimmune conditions [5]. Sources: [1] UniProt (P02976); [2] Falugi et al. (2013) mBio; [3] XBiotech (514G3); [4] Kim et al. (2010) JEM; [5] FDA (Prosorba).

Other names

Protein AImmunoglobulin-binding protein ASpAStaphylococcal protein A

Monoclonal antibodies bind to SpA to block its interaction with the Fc region of IgG and the VH3-type B-cell receptor, thereby restoring opsonophagocytic clearance and preventing B-cell apoptosis [2, 3]. In extracorporeal treatments, immobilized Protein A is used to remove IgG and immune complexes from the blood to reduce inflammation in autoimmune diseases [5].