Biopharmaceuticals on Instagram: "🧪 The Gold Standard: Protein A Chromatography Explained If you are in downstream processing (DSP), this molecule is your best friend. Here is the breakdown of the primary capture step for Monoclonal Antibodies (mAbs). 1. The "Lock and Key" Mechanism Protein A is a cell wall protein originally found in S. aureus. It has an incredibly high affinity for the Fc (Fragment crystallizable) region of IgG antibodies. This high specificity is why we can achieve >9