Introduction to Aptamers

Monoclonal antibody production technology was developed in 1975. It can be used not only in basic science, but also in the fields of drugs and biosensors, and has great significance in medicine. The world's first therapeutic antibody was discovered in 1986 to prevent kidney transplant rejection. Since then, many antibody drugs have been found to be used to treat various diseases, such as asthma. However, monoclonal technology has certain limitations in treating diseases. For example, antibodies against lipids, carbohydrates and organic macromolecules have low affinity, and the affinity of drug coupling is affected to a certain extent. Therefore, artificial ligands-aptamers are gradually emerging.

An aptamer is a single-stranded nucleic acid molecule that can specifically bind to a variety of targets. It has the unique advantages of small size, low cost, simple and uniform synthesis, easy customization and modification, and as a nucleic acid template. These characteristics make aptamers have a wide range of application potential in target selection. For example, small molecule and ion aptamers can effectively supplement the deficiencies of traditional antibodies and provide more options. As an emerging artificial ligand, aptamers have shown great application prospects in fields such as biomedicine and drug development.

Nucleic acid aptamers are a class of single-stranded DNA or RNA molecules composed of 20 to 110 nucleotides, including random sequences and fixed sequences. Through self-folding, they form high-affinity small molecule groups with tertiary structures, which can specifically bind to target molecules. In recent years, nucleic acid aptamers have made significant progress in the field of small molecule sensing analysis and detection, and are widely used in many fields such as food safety, environmental monitoring and biological analysis, showing their unique potential and application value.

Introduction to Proteins and Nucleic Acid Aptamers

Proteins exist in all biological molecules and establish complex connections with various molecular substances (from single atoms/ions to huge macromolecules). The interaction between molecules is highly specific and plays an important role in living organisms. Since only a few atoms interact when small molecules bind to proteins, nucleic acid aptamer technology has emerged.

The interaction between nucleic acids and proteins plays a vital role in basic cellular processes. Polynucleotides based on DNA or RNA have the ability to specifically target proteins, and the targeting range is wide, including proteins that do not participate in interactions with nucleic acids under physiological and pathological conditions. Changing the structure of aptamers can regulate the interaction with proteins and further affect related pathways.

The first structural characterization of protein-aptamer complexes was reported many years ago, but progress has been slow until now. Van der Oost performed a preliminary analysis of protein-aptamer complexes in 2012. In 2016, a study characterizing the structural theme of protein aptamer recognition described only 16 protein-aptamer complexes at the time. Recently, Novoseltseva et al. investigated the structures of 45 such complexes.

In recent years, with the in-depth study of aptamer-protein interactions, nucleic acid aptamer screening technology has been widely developed and has become a powerful tool for biomolecule detection. Targeted protein degradation is of great significance in the fields of chronic diseases, rare diseases, and cancer research. Therefore, aptamers have been actively used in the design and construction of targeted protein degradation technologies. For many years, there was only one aptamer-based drug on the market, pegaptanib sodium (Macugen by Pfizer/Eyetech), which was approved by the FDA in 2004 for the treatment of macular degeneration. Recently, the FDA approved a second RNA aptamer, avacincaptad pegol (produced by Iveric Bio/Astellas), for the treatment of geographic atrophy secondary to age-related macular degeneration.

Nucleic Acid Aptamer Screening Technology for Proteins

①. Aptamer Sequence Design

The results of SELEX screening are related to the design of the library, so the aptamer sequence design is crucial. It is generally recommended to control the nucleic acid chain length within 300 bp/nt. Because too long nucleic acid molecules will have multiple different binding sites to bind to proteins, there are situations where existing models cannot be used to fit. Therefore, it is recommended to use relatively short nucleic acid fragments (i.e., the core region involved in binding) for interaction studies.

②. Fix Protein or Nucleic Acid

Both can be fixed, depending on the nature of the sample and the purpose of the experiment.

If the protein sample is impure, the protein can be fixed by capture method; if the affinity of different types of proteins and nucleic acid molecules needs to be tested, the nucleic acid is fixed; if the aptamer with high affinity between the nucleic acid library and protein needs to be screened, the protein is fixed.

Screening Methods for Nucleic Acid Aptamers of Proteins

The following are methods for screening nucleic acid aptamers for small molecule targets:

1. Screening Technology based on Target Fixation

After development, the in vitro screening technology of aptamers based on target fixation has solved the problems of non-specific binding of aptamer libraries, exposure of target binding sites, poor affinity, chemical modification, etc.

2. Screening Technology based on Library Fixation - Capture-SELEX

The Capture SELEX screening technology overcomes the above technical problems. The aptamer library of this method consists of three parts: random sequence, docking sequence and primer sequence.

3. Homogeneous Screening Technology

Homogeneous screening technology improves the screening efficiency, and the screened nucleic acid aptamers can be converted into sensors.

4. Automated SELEX

The traditional SELEX screening method has a long cycle, and automated SELEX screening improves the efficiency of aptamer screening. Studies have shown that a variety of tumor or disease-related proteins are selected for counter-screening, coupled with magnetic beads through chemical modification, and then incubated with nucleic acid libraries, and the target protein is screened through multiple rounds of washing-elution.

TekBiotech has made remarkable achievements in the research and application of aptamers, successfully completed a number of aptamer projects, and accumulated rich technical experience and practical application cases. With its mature technology platform, TekBiotech can provide customers with efficient and customized services, especially in the screening and development of aptamers. The company also provides customized SELEX screening technology to help customers accurately screen out high-affinity and specific aptamers according to different research needs.

In addition, TekBiotech also provides customers with one-stop services, including antibody expression and purification, affinity determination, antibody sequencing, etc. Through these services, TekBiotech can not only meet customers' personalized needs in the research and development of aptamers, but also provide customers with high-quality and comprehensive technical support to promote customers' scientific research progress and product development.