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Synthetic affinity ligands can circumvent the drawbacks of natural immunoglobulin (Ig)-binding proteins by imparting resistance to chemical and biochemical degradation and to in situ sterilization, as well as ease and low cost of production. Protein L (PpL), isolated from Peptostreptococcus magnus strains, interacts with the Fab (antigen-binding fragment) portion of Igs, specifically with kappa light chains, and represents an almost universal ligand for the purification of antibodies. The concepts of rational design and solid-phase combinatorial chemistry were used for the discovery of a synthetic PpL mimic affinity ligand. The procedure presented in this chapter represents a general approach with the potential to be applied to different systems and target proteins.

The current chromatographic approaches used in protein purification are not keeping pace with the increasing biopharmaceutical market demand. With the upstream improvements, the bottleneck shifted towards the downstream process. New approaches rely in Anything But Chromatography methodologies and revisiting former techniques with a bioprocess perspective. Protein crystallization and precipitation methods are already implemented in the downstream process of diverse therapeutic biological macromolecules, overcoming the current chromatographic bottlenecks. Promising work is being developed in order to implement crystallization and precipitation in the purification pipeline of high value therapeutic molecules. This review focuses in the role of these two methodologies in current industrial purification processes, and highlights their potential implementation in the purification pipeline of high value therapeutic molecules, overcoming chromatographic holdups.