Fab Antibody Production Service

Antigen binding fragments (Fab), are from the enzymatic or chemical digestion of a full size antibody (such as a IgG). These fragments are the antigen-binding domains of an antibody molecule, containing a variable region of heavy chain (VH), a variable region of light chain (VL), a constant region of heavy chain 1 (CH₁) and a constant region of light chain (CL) [1]. Fab fragments can be obtained in two ways: via recombinant synthesis or enzymatic cleavage of the parent antibody [2].

With years of research experience in the field of recombinant antibody construction and expression, Biologics International Corp (BIC) offers antibody fragment production services, which include Fab, scFab, Fab’, F(ab’)₂, scFv, diabody, triabody, minibody, and scFv-Fc production. Do not hesitate to get in touch for any further information regarding antibody fragments. We are always glad to assist you.

Fab

Fab fragments with a size of around 50 KDa are the antigen-binding domains of an antibody molecule, containing one constant and one variable domain of each of the heavy and the light chains. The fragments which contain disulfide bridge thiols are called Fab’ fragments, whereas those lacking the thiol functional group are termed Fab fragments [2]. Because of their small sizes, Fab/Fab’ can penetrate tissues more efficiently and be cleared from the blood more rapidly. As they do not have Fc fragments, Fab/Fab’ will not interfere with anti-Fc mediated antibody detection.

Fab Fragments Construction

To produce Fab fragments, two different methods can be employed. The primary method is via enzymatic/chemical cleavage of the whole antibody, in which the whole antibody is cleaved by enzyme (such as papain, pepsin, and ficin) to form F(ab’)₂ fragments, followed by the reduction of those fragments to yield Fab fragments [2]. An alternative method is through the recombinant synthesis of F(ab’)₂ antibody fragments, followed by chemical reduction of these fragments to yield Fab units.

Fab Antibody Library

Currently, most recombinant antibody fragments are generated by phage display antibody libraries [3]. Fab antibody library is advantageous in several important ways: first, compared with monoclonal antibodies, which is very laborious and time-consuming to produce, Fab antibody library can rapidly and efficiently select new antibodies that are difficult to gain through hybridoma technology. Second, like scFv antibodies, it could be easier to generate Fab antibodies with higher affinities. Third, advantages of Fab fragments are highly stable under long term storage [4] and are compatible with common detection antisera without the need for re-engineering. If you need an antibody against some unusual antigens, get in touch, our antibody library with rich diversity and large scale will help you to find an ideal antibody.

More Fab Formats

A F(ab')₂ fragment, which retains a small part of the Fc hinge region, has two antigen binding regions that may increase the affinity to antigen. Reduction of F(ab')₂ fragments produces two monovalent Fab' fragments, which have a free sulfhydryl group that is useful for conjugation with other molecules.

Although the utilization of enzymatic/chemical cleavage methods to generate Fab fragments is convenient and efficient, it requires a large quantity of monoclonal antibody as starting material. A single-chain Fab fragment (scFab) can lead to improved function and production of Fab fragments. According to some studies [3], scFab fragments show superior antigen-binding ability compared to Fab and compensate for some of the disadvantages of the soluble Fab production in E. coli.

Have some antibody formats in mind? Contact us with your ideas, let us see what we can do for you.

Fab vs. scFv Fragment

Fragment Type	scFv	Fab
Composition	VH, VL	VH, VL,CH1, CL
M.W. (kDa)	30	50
Blood clearance	Very rapid	Rapid
Tumor penetration	Great	Good
Retention times	Very short	Short
Affinity	Reduced	Better than scFv
Stability	Unstable over longer periods	High stability in long-term storage
Production	Recombinant methods Easy for expressing in various systems	Enzymatic and recombinant methods Less efficient folding and assembly in E. coli

References

1. Vivi Joosten, Christien Lokman, et al. The production of antibody fragments and antibody fusion proteins by yeasts and filamentous fungi. Microbial Cell Factories, 2003, 2:1.
2. Victor Crivianu-Gaita, Michael Thompson. Aptamers, antibody scFv, and antibody Fab fragments: an overview and comparison of three of the most versatile biosensor biorecognition elements. Biosensors and Bioelectronics, vol.85, 2016, pp.32-45.
3. Michael Hust, Thomas Jostock, et al. Single chain Fab (scFab) fragment. BMC Biotechnology, 2007, 7:14.
4. Karl Kramer, Markus Fiedler, et al. A generic strategy for subcloning antibody variable regions from the scFv phage display vector pCANTAB 5 E into pASK85 permits the economical production of Fab fragments and leads to improved recombinant immunoglobulin stability. Biosensors & Bioelectronics, vol.17, 2002, pp.305-313.

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