Creative Biolabs is glad to provide single domain antibody (sdAb) stability improvement service for our client all over the world. With the consistent growth of therapeutic sdAb in the global market, it is important for improving the safety, reliability, and stability of the discovered sdAbs. As stability is one of the most important requirements in the application of therapeutic and diagnostic, Creative Biolabs has developed a remarkable platform for sdAb stability improvement which would be helpful for your sdAb discovery and development projects.

Background

Single domain antibodies (sdAbs) are antibody fragment consisting of a single monomeric variable antibody domain, derived from the heavy-chain-only antibodies produced by camelids and sharks, or the specific developed human V_H and V_L domain. SdAbs, with a molecular weight of only ~15 kDa, are much smaller than other antibodies. Due to the characteristics of small size, simple production, and high affinity, sdAb allows a broad range of applications in biotechnical and therapeutic use. While like other conventional antibodies, the stability is still one important factor for the sdAb, especially for those developed from human V_H and V_L domain.

The in vitro stability of sdAbs can be defined by two concepts, the physical stability (thermodynamic stability) and the chemical stability (proteolytic stability). In general, sdAbs are known to be signally stable compared with conventional antibodies. However, it is still necessary to extend the application of sdAbs in extreme environments against temperature induced denaturation, pH induced denaturation, protease hydrolysis and mechanical shear stress to achieve a variety of goals of research and investigation.

Fig. 1 Disulfide-bond Stabilized sdAb. (Hagihara et al. 2012)

Single Domain Antibody Stability Improvement Service

With years of experience, Creative Biolabs has developed efficient methods to improve the stability of sdAb. On the one hand, an elegant solution is based on two amino acid substitutions within the framework to form an additional intra-domain disulfide bond while having minimal effects on antigen affinity. On the other hand, CDR is grafted onto the stable framework. Commonly, untargeted mutagenesis and phage display screening at appropriately stringent conditions. In addition, a method is provided to predict the proteolytic susceptibility of sdAb and to subsequently increase the proteolytic stability through genetic engineering as well. Meanwhile, we are also flexible enough to discuss the proposal with our customers or follow a published one to fulfill your specific demands.

Fig. 2 Topical Process of sdAb Mutagenesis.

Creative Biolabs has been a long-term expert in the field of sdAb stability improvement. Our service can be tailor-designed to meet your specific needs. Our seasoned scientists are confident in offering the best service for our customers. If you are interested in our sdAb stability improvement service, please do not hesitate to inquire us for more details.

Reference

1. Hagihara, Y.; Saerens, D. Improvement of single domain antibody stability by disulfide bond introduction. Single Domain Antibodies: Methods and Protocols. 2012, 399-416.

Published Data

• Analysis of the CDRs to the Thermal Stability of SdAbs

Fig. 3 CDR swaps lower affinity but may increase or decrease melting temperature. (Dan Zabetakis, 2013)

Single-domain antibodies have excellent affinity and specificity, and most of them are refolded and can bind to antigens after thermal denaturation. SdAb A3 was selected from the phage display sdAb library of immunized llama and showed high affinity and specificity for staphylococcal enterotoxin B (SEB). In this article, the researchers constructed a series of CDR exchange mutants, in which the CDRs from unrelated sdAb were integrated into the framework of A3, and the CDRs of A3 were integrated into other sdAb frameworks. All three CDRs from A3 were moved to the frameworks of sdAb D1 (a ricin binder) and anti-ricin sdAb C8. Similarly, CDRs from sdAb D1 and sdAb C8 are moved to the sdAb A3 framework. They evaluated the unchain temperature and binding capacity of each CDR exchange mutant. The results show that CDR2 plays a key role in the binding and stability of sdAb A3. In general, the results of CDR exchange show that CDR interaction plays an important role in protein stability.

FAQ

1. What is the stability of single-domain antibodies?

   Single-domain antibodies have a recombinant antibody structure that usually contains only one antigen-binding domain (the single variable region). Compared with the traditional complete antibody, its structure is simpler. However, single-domain antibodies may have stability problems under some conditions, including temperature changes, pH changes, extreme ionic strength, and so on. These stability problems may lead to structural changes or degradation of antibodies, thus affecting their activity and potency.

2. How to improve the stability of single-domain antibodies?

   Choose the appropriate antibody framework: the appropriate antibody framework is very important to improve the stability of single-domain antibodies. By selecting an antibody framework with good stability, the structural change and degradation risk of single domain antibodies in the process of preparation and storage can be reduced.
   Structural optimization: the structure of single-domain antibodies is optimized by protein engineering technology, including adjusting amino acid sequence, introducing stable mutants, or changing the glycosylation mode of proteins.
   Use of stabilizing reagents: when preparing and storing single-domain antibodies, some stabilizers can be added to improve their stability. These stabilizers can include glucose, glycerol and amino acids, which can protect single-domain antibodies from the external environment such as temperature, pH value, and ionic strength.
   Use appropriate storage conditions: the correct storage conditions are essential to maintain the stability of single-domain antibodies. It is generally recommended to store single-domain antibodies at low temperatures (4 °C or less) and under aseptic conditions to reduce their degradation and denaturation during storage.

3. What are the reasons that may affect the stability of single domain antibodies?

   Temperature change: protein denaturation or aggregation may occur at high temperatures, resulting in a loss of biological activity.
   The change of pH value: the change of acid-base environment may cause conformational change or chemical denaturation of single-domain antibodies.
   Oxidation: oxidation is a common problem in the stability of single-domain antibodies, which may lead to oxidative modification of proteins, thus affecting their biological activity and pharmacological properties.
   Repeated freeze-thaw: frequent freeze-thaw cycles may damage the stability of single-domain antibodies and lead to protein aggregation or degradation.
   The change of ionic strength: the change of ionic strength may affect the charge state and solubility of a single domain antibody and then affect its stability and activity.

4. What are the biophysical properties that need special attention in the process of improving the stability of single-domain antibodies?

   It includes the hydrophobicity, charge distribution, glycosylation state, and special structure of the amino acid sequence of the antibody. The increase in hydrophobicity may enhance the internal stability of the antibody and reduce the tendency for aggregation in an aqueous solution. The reasonable design of charge distribution can affect the stability of antibodies at different pH values, thus reducing the risk of aggregation or degradation. Glycosylation also has an important effect on the solubility and stability of antibodies, so it needs to be controlled in the preparation process. In addition, special amino acid sequence structures, such as oxidizable cysteine residues, also need to be considered in the design and optimization process.

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