In terms of extensive experience in the field of single domain antibody (sdAb) discovery and development, Creative Biolabs has built up a novel intrabody discovery platform to screen and validate novel sdAbs that can specifically bind to intracellular targets within various cellular compartments. Our professional scientists can utilize either the yeast or the mammalian two-hybrid system to screen the sdAb library and validate the specific intrabodies.

Background

In recent years, specific antibodies against extracellular or cell surface targets are the fastest-growing new class of therapeutic molecules in the biomedical and pharmaceutical industries. However, the majority of potential therapeutic targets are intracellular, while most antibodies cannot readily recognize such molecules because of the inability to form stable structures in the intracellular environment. Intrabodies are a class of antibodies that can bind to intracellular antigens and function in the intracellular environment. They are directed against intracellular target molecules and expressed within a specific subcellular compartment as directed by the intracellular localization signals genetically fused to N- or C-terminus. Intrabodies have wide applications in dissecting target protein function, in target validation and functional genomics, as well as acting as potential therapeutic reagents.

Compared with other conventional antibody formats (e.g. full length, Fab, scFv), single domain antibody which is an antibody fragment consisting of a single monomeric variable antibody domain, has indicated greater developability and manufacturability as a new candidate for intrabody discovery. As a novel antibody format, the comparatively low molecular mass of sdAb (~15 kDa) leads to better permeability in tissues. Unlike full-length antibodies, sdAbs do not show complement system triggered cytotoxicity because they lack the Fc region. SdAbs derived from either camelid or cartilaginous fishes take advantage of high stability under extreme conditions (e.g. high temperature, acidic or alkaline conditions). In addition, they can bind to hidden epitopes that are not accessible by conventional antibodies, for example to the active sites of enzymes. This property has been shown to result from their extended CDR3 loops, which contribute to penetrating such sites.

Yeast Two-Hybrid Method

The yeast two-hybrid system is an in vivo genetic method used to detect protein-protein interactions. In this system, the antigen protein (referred to as the "bait") is fused with the Gal4 DNA binding domain (DNA-BD), while single domain antibodies (sdAbs) engineered from heavy chain antibodies found in camelids are fused to the Gal4 activation domain (AD). When the antigen and antibody library fusion proteins interact, the DNA-BD and AD come into proximity, activating the transcription of reporter genes. This approach allows for the discovery of high-affinity single domain antibodies specific to the antigen. Intrabodies discovered on this platform are expressed and selected within yeast cells, often recognize the native conformation of the antigen and have direct therapeutic potential.

Fig. 1 Schematic representation of yeast two-hybrid method.

Features of Our Intrabody Discovery Service

• Recognizes the native conformation of the antigen.
• In vivo antigen expression rather than purified protein form.
• Specific antibodies can be validated in a high-throughput or more precise manner.
• Better targeting of proteins and domain binders that are unstable or difficult to obtain in vitro.
• Flexible system selection to obtain the most specific and affinity intrabodies.

Published Data

• Intrabody-Induced Cell Death by Targeting Tb BILBO1 Protein

Fig. 2 SdAbs as Tb BILBO1 immunofluorescence detection tools.¹

Trypanosoma brucei, a type of protist, poses health risks as a zoonotic parasite in Sub-Saharan Africa. Scientists investigated the cytoskeleton (the cell's internal skeleton) of these parasites, focusing on the essential protein BILBO1. To create targeted antibodies, they immunized alpacas with full-length Tb BILBO1 protein. These antibodies, known as single-domain antibodies (sdAbs), were then tested and expressed as intrabodies. Remarkably, these functional intrabodies accurately bind to Tb BILBO1, disrupting cytoskeleton formation and leading to rapid cell death.

• Selection of a Single Domain Intrabody Against TDP-43

Fig. 3 Selection of anti-TDP-43 intrabody.²

Amyotrophic lateral sclerosis (ALS), a devastating neurodegenerative disease, results from neuronal death. The culprit is the protein TDP-43, which plays crucial roles in DNA/RNA binding and nucleic acid metabolism. Unfortunately, in ALS patients, TDP-43 aggregates within neurons, turning toxic. Researchers have made significant strides in combating this toxicity. They have harnessed V_HH antibodies (intrabodies) from llamas, specifically targeting TDP-43. These intrabodies work inside cells, blocking toxic TDP-43 and promoting its degradation. By predicting the structure of these intrabodies using computational models, scientists suggest mutations that enhance their expression. Their findings clarify strategies for alleviating TDP-43 protein disease in ALS and provide potential new tools for diagnosis.

Creative Biolabs is convinced that collaborating with our customers is the best way to share our full knowledge and experience. Our seasoned scientists are pleased to offer custom services for our clients to stratify the specific needs and expectations of their valuable projects. If you are interested in discovering your intrabodies, please feel free to inquiry us for more details.

FAQ

1. What is an intrabody?

   Intrabody, or endogenous antibody, is a fragment of antibody expressed in cells. They are usually single-domain antibodies (sdAb), single-chain variable fragments (scFv), or other small antibody variants, which enable them to stably exist and function in the cytoplasm. Intrabodies can specifically bind to the target protein, thus interfering with its function, and can be used in the treatment of diseases, the study of protein function, and as a biotechnology tool.

2. What are the applications of Intrabody?

   Intrabodies are mainly used for research and treatment. In basic research, they can be used to block the function of specific proteins and help scientists understand the role of these proteins in cells. In the medical field, intrabodies can be used to treat a variety of diseases, especially those involving misfolded or overexpressed proteins, such as neurodegenerative diseases and certain types of cancer. Their high specificity and ability to reach inside cells make them a promising therapeutic tool.

Resources

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