What is Whole-cell SELEX? Whole-cell SELEX (Systematic Evolution of Ligands by EXponential enrichment) is a technique used to discover aptamers (single-stranded DNA or RNA molecules) that bind specifically to a target living cell. Unlike traditional SELEX that uses a purified protein target, whole-cell SELEX presents the target in its native, complex cellular environment. This allows for the selection of aptamers against: Native cell-surface proteins in their proper folding and post-translational modifications. Complex targets like transmembrane receptors in their natural lipid environment. Unknown surface biomarkers without prior knowledge of the cell's molecular makeup. Specific cell states (e.g., activated, cancerous, infected) based on differences in surface expression. The Core Process: How Whole-cell SELEX Works A professional service will manage this complex, iterative pipeline: Library & Design: Starting with a vast, random synthetic oligonucleotide library (10^14 - 10^15 unique sequences). Positive Selection: Incubating the library with the target cells (e.g., cancer cells, stem cells, bacteria). Aptamers that bind to any surface structure are retained. Counter-Selection (Critical Step): The bound pool is then exposed to non-target or control cells (e.g., healthy cells, a different cell line). Sequences that bind to these are discarded. This step is crucial for generating specificity. Elution & Amplification: Aptamers specifically bound to the target cells are recovered, amplified by PCR…
What is Solution-Phase SELEX? SELEX (Systematic Evolution of Ligands by EXponential Enrichment) is the iterative process used to discover aptamers—single-stranded DNA or RNA molecules that bind to a specific target with high affinity and specificity. Solution-Phase SELEX refers to performing the selection process with the target molecule free in solution, rather than immobilized on a solid surface (like beads or a column). This often involves a partitioning step that separates bound from unbound sequences using a method like filtration, capillary electrophoresis, or magnetic bead capture of the target. Key Advantages of Solution-Phase SELEX Preservation of Native Target Conformation: The target is in its natural, free state in solution. This is crucial for complex targets like membrane proteins, which can denature or present epitopes unnaturally when immobilized. Access to All Binding Sites: All surfaces of the target are available for aptamer binding, increasing the diversity of potential aptamers discovered. Avoidance of Non-Specific Binding to Solid Support: Reduces background noise from library sequences sticking to the immobilization matrix (e.g., sepharose beads, plastic wells), leading to cleaner selections. Better for Small Molecules and Peptides: Ideal for targets that are difficult to immobilize without blocking their functional groups. Mimics Physiological Conditions: More closely replicates how the aptamer will interact with its target in real-world applications…
