Post-Translational Modifications (PTMs) are chemical modifiers that act to influence protein function. PTMs can turn activities on and off, like a switch, can strengthen or weaken structure, influence stability, and affect many protein-protein interactions, enzymatic activities. PTMs of interest include methylation, phosphorylation, glycosylation, acetylation, ubiquitination, citrullination and others.

Changes in protein phosphorylation of p53 and other oncogene proteins are involved in up to 90% of cancers. Thus, when studying behavior of these proteins in SPOC and other formats, it is vital to have properly modified proteins.

SPOC has three approaches to adding PTMs to arrays of SPOC proteins.

1. SPOC proteins are expressed in a mammalian cell-derived expression system in which native PTMs are encouraged to form (e.g. N-glycosylation)
2. Enzymes and co-factors required for PTMs may be included in the mammalian expression system to help form specific PTMs
3. Following protein synthesis of SPOC arrays, specific protein-modifying enzymes may be added to affect protein modification (e.g. citrullination)