Core Technology: SELEX The foundation of all these services is the SELEX process, an in vitro method to select aptamers from a vast random library (typically 10^13 - 10^15 unique sequences). The library is incubated with the target, unbound sequences are washed away, and bound sequences are eluted and amplified by PCR (for DNA) or RT-PCR (for RNA). This cycle is repeated 8-15 times to enrich for the tightest binders. Services for Protein Targets This is the most common application, as aptamers are often touted as "chemical antibodies." 1. Standard Protein SELEX: Target: Purified, recombinant proteins (e.g., cytokines, receptors, enzymes, viral capsids). Key Considerations: Protein Purity & Conformation: Critical for success. Services often require >90% purity and verification of native folding. Immobilization: The protein is usually immobilized on beads (e.g., streptavidin/biotin, Ni-NTA/His-tag) to facilitate partitioning. Some services offer solution-phase SELEX to avoid conformation changes. Counter-Selection: To ensure specificity, libraries are pre-incubated with related proteins or the immobilization matrix to subtract non-specific binders. 2. Specialized SELEX for Complex Proteins: Membrane Protein SELEX: For receptors and channels. Requires special handling (e.g., use of nanodiscs, detergent micelles, or whole cells overexpressing the target). Post-Translationally Modified Protein SELEX: For targets where phosphorylation, glycosylation, etc., are essential for function. 3. Cell-SELEX (for Cell-Surface…
