What is Small Molecule SELEX? SELEX is an iterative in vitro selection process that sifts through a vast random library of nucleic acid sequences (typically 10^13 - 10^15 different molecules) to find the few that bind tightly and specifically to a target. The Challenge with Small Molecules: Low epitope density: Small molecules offer limited surface area for binding, making it hard to find high-affinity aptamers. Immobilization required: They must be attached to a solid support (beads, chip, column) for partitioning, which can mask potential binding sites or introduce non-specific interactions. Negative Selection is Crucial: To avoid selecting aptamers that bind to the immobilization matrix instead of the target. Standard Service Workflow (What the Provider Does): Project Design & Target Immobilization: Consultation: The provider works with you to understand the target's chemistry, desired affinity, and application (e.g., biosensor, therapeutic inhibitor, diagnostic). Conjugation: They chemically conjugate your small molecule to an appropriate carrier (e.g., beads, magnetic particles, agarose resin, or a surface like a chip). This is a critical, proprietary step for many providers. The SELEX Cycle (Repeated 8-15 rounds): Incubation: The vast oligonucleotide library is incubated with the immobilized target. Partitioning: Unbound sequences are washed away. Sequences bound to the target (and unfortunately, sometimes to the matrix) are retained. Elution: Bound…
Core Concept The central idea is "Target-based Drug Discovery." Instead of screening compounds on whole cells or organisms (phenotypic screening), you start with a specific protein (e.g., a kinase, receptor, ion channel) implicated in a disease. Services then help you understand that target and find molecules that modulate it. Categories of Protein Target Services These services typically follow the drug discovery pipeline: 1. Target Identification & Validation Bioinformatics & Omics Analysis: Mining genomic, proteomic, and clinical data to identify novel disease-associated targets. Genetic Validation: CRISPR/Cas9 gene editing (knock-out/knock-in), siRNA/shRNA knockdown to confirm the target's role in disease pathways. Functional Validation: Cell-based assays to see if modulating the target affects disease-relevant phenotypes. 2. Protein Expression & Purification Recombinant Protein Production: Cloning, expressing (in E. coli, insect, or mammalian cells), and purifying milligram to gram quantities of the target protein. This is essential for structural studies and biochemical assays. Membrane Protein Expertise: Specialized services for difficult-to-express targets like GPCRs and ion channels. Tagging & Labeling: Adding tags (His, GST, FLAG) for purification or fluorescent/isotopic labels for assays. 3. Structural Biology & Biophysics X-ray Crystallography: Determining high-resolution 3D structures of protein-ligand complexes. Cryo-Electron Microscopy (Cryo-EM): For large complexes or membrane proteins unsuitable for crystallography. Nuclear Magnetic Resonance (NMR) Spectroscopy: For studying dynamics and ligand binding in solution. Surface…
Traditional SELEX (Systematic Evolution of Ligands by EXponential enrichment) is a method to select high-affinity, specific nucleic acid aptamers from a vast random library (10¹³-10¹⁵ sequences). The bottleneck has always been the final cloning and Sanger sequencing of only a few dozen candidates, which often misses rare, high-performance aptamers. NGS-assisted SELEX integrates Next-Generation Sequencing at multiple rounds of the SELEX process. This provides a massive, data-rich view of the entire evolutionary landscape, enabling intelligent selection and identification of the best aptamers. Typical Workflow of an NGS-Assisted SELEX Service A professional service provider will manage this entire pipeline: Project Design & Library Synthesis: Collaboration to define target (protein, small molecule, cell), counter-selection requirements, and library design (random region length, fixed primers for NGS). Parallel SELEX Execution: Performing the iterative selection process (binding, partitioning, amplification) across multiple rounds (usually 8-12). Key NGS Integration Points: Initial Library Analysis: Sequencing the naive library to confirm diversity and complexity. Monitoring Rounds (e.g., Rounds 3, 6, 9): Taking small samples from intermediate rounds for NGS. This is the critical advantage. It tracks: Sequence Enrichment: Which families are becoming more abundant. Diversity Collapse: When to stop selection before losing good candidates. Informed Decision-Making: Data guides adjustments in selection stringency for subsequent rounds. Final Round Deep Sequencing: Comprehensive NGS of…
Aptamer Capture-SELEX Service refers to a specialized, outsourced process where a company or academic core facility performs the entire Capture-SELEX procedure to develop DNA or RNA aptamers for a client's specific target molecule. This is a crucial service for researchers and companies who need high-affinity, specific aptamers but lack the specialized equipment, expertise, or time to run the SELEX process in-house. Let's break down what this service entails. 1. What is Capture-SELEX? First, understand the standard SELEX (Systematic Evolution of Ligands by EXponential enrichment). It's an iterative process to select aptamers from a vast random oligonucleotide library (10^14 - 10^15 different sequences). Capture-SELEX is a specific variant designed primarily for small molecules or targets that are difficult to immobilize directly on a solid support without affecting their structure/function. The Key Difference: Instead of immobilizing the target itself, a short, complementary "capture strand" is immobilized on beads or a surface. The initial ssDNA library is designed with a region complementary to this capture strand. The target is free in solution. How it Works: The library is bound to the surface via the capture strand. The target molecule is introduced in solution. Only library sequences that fold into a structure capable of binding the target will undergo a conformational change. This binding event often weakens or…
What is Live Cell SELEX? Traditional SELEX uses purified target proteins. Live Cell SELEX uses intact, living cells in their native state. This is crucial because: It selects for aptamers that bind to targets in their natural conformation and post-translational modifications (e.g., glycosylation). It inherently selects for cell-specificity (e.g., cancer cell vs. healthy cell) without needing to know the exact molecular target upfront. It can discover aptamers against unknown or membrane-bound targets that are difficult to purify. Core Workflow of a Typical Service A full-service provider will manage the entire pipeline: 1. Project Design & Consultation Target Cell Line Definition: Defining the "positive" cell line (e.g., patient-derived cancer cells, activated immune cells). Counter-Selection Strategy: Choosing the "negative" cell line(s) (e.g., healthy counterpart, isogenic control) to eliminate non-specific binders. Library Design: Recommending or customizing the starting random oligonucleotide library (length, modifications like 2'-F pyrimidines for RNA aptamers for stability). 2. The Selection Phase (The Iterative SELEX Cycles) Incubation: The random library is incubated with the counter-selection cells. Unbound/non-specific sequences are collected. Positive Selection: The pre-cleared library is incubated with the target cells. Cells are washed stringently. Recovery: Cell-bound aptamers are recovered (e.g., by cell lysis, heat elution, or protease treatment). Amplification: Recovered sequences are amplified by PCR (for DNA) or RT-PCR (for…
CUSTOM APTAMER DISCOVERY & DEVELOPMENT is the process of creating target-specific single-stranded DNA or RNA aptamers—short nucleic acids that fold into 3D shapes capable of binding proteins, small molecules, cells, vesicles, or other targets with antibody-like selectivity. Most custom programs rely on SELEX (Systematic Evolution of Ligands by EXponential enrichment), then refine “hits” into robust, application-ready binders through sequencing-driven analysis and post-selection optimization. 1) What Aptamers Are (and Why They’re Used) Aptamers are typically ~15–90 nucleotides long and can be engineered to bind targets across a wide size range (from small molecules to whole cells). They’re attractive because they are chemically synthesized (batch-to-batch consistency), can be readily labeled (fluorophores, biotin, etc.), and are generally thermally stable and re-foldable—features that often simplify assay development and manufacturing. Common aptamer use cases Diagnostics & biosensors (capture probes, signal transducers, point-of-care formats) Targeted delivery & therapeutics research (cell-directed binding, payload delivery concepts) Affinity purification & analytical workflows (pull-downs, enrichment, separations) 2) The Core Workflow in Custom Aptamer Discovery A custom program is best thought of as a pipeline with four linked decisions: target format → selection strategy → analytics → optimization. Step A — Target Definition and “Bindability” Planning…
