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…
What is an Aptamer? First, a quick reminder: Aptamers are short, single-stranded DNA or RNA oligonucleotides that bind to a specific target with high affinity and specificity. They are often called "chemical antibodies." The Core Service: SELEX (The Screening Process) The service revolves around executing a SELEX (Systematic Evolution of Ligands by EXponential enrichment) campaign. This is an iterative, in-vitro combinatorial chemistry process that screens a vast random library (10^14 - 10^15 unique sequences) to find the few that bind your target. A standard SELEX workflow includes: Library Design & Synthesis: Creating the initial random oligonucleotide pool. Incubation: The library is exposed to the target. Partitioning: Bound sequences are separated from unbound ones (the most critical step, varying by target type). Amplification: The bound sequences are amplified (usually by PCR for DNA, RT-PCR for RNA). Counter-Selection (Negative Selection): To increase specificity, the pool is exposed to non-target surfaces (e.g., immobilization matrix, related proteins) to remove non-specific binders. Repetition: Steps 2-5 are repeated for 8-15 rounds until a high-affinity pool is enriched. Cloning & Sequencing: The final pool is cloned, and individual aptamer sequences are identified via Next-Generation Sequencing (NGS). Bioinformatics & Analysis: NGS data is analyzed to identify candidate sequences, often clustered into families based on sequence/structure motifs. Characterization: Top candidates…
