Proteins are composed of amino-acid subunits that through various inter-molecular forces produce well-defined, three-dimensional structures. This process called protein folding can be spontaneous and occur co-translationally, yielding mature and active protein molecules.
Proper folding ensures that key amino-acid subunits are oriented properly in 3-D space to form active sites for substrate binding, catalytic sites producing enzymatic activity, or binding motifs or epitopes that direct interactions with complementary partner biomolecules. Protein misfolding can drastically influence protein function leading to loss of activity or to aberrant activity as observed in neurodegenerative diseases where mis-folded proteins form disruptive amyloid fibrils.
To achieve properly folded and fully functional proteins, the SPOC platform is compatible with a variety of antibody-based and covalent capture tag chemistries that suit customer’s needs. Importantly, the covalent capture tag needs to be expressed in-frame and requires proper folding for covalent attachment to the capture ligand coated biosensor. Therefore, only fully folded proteins are captured onto the chip surface for downstream assays.
Ultimately all strategies yield monolayers of expressed proteins captured onto discrete regions of the biosensor surface with consistent, external orientation of proteins of interest. Additionally, each SPOC biosensor contains a QC set of proteins that can be used for validating array activity by assaying for epitope presentation (antibody binding), proper substrate formation (citrullination), protein – protein interaction (Fos binding to Jun), and enzymatic activity (autophosphorylation).