Fab and F(ab') 2 from whole lgG
Antibody fragments are functional regions of whole immunoglobulin consisting of the antigen binding fragment (Fab) and the crystallizable fragment (Fc). Fabs may be used to bind their target antigen without directing an immune response, resulting in extremely controlled and pointed targeting. Removal of the crystallizable or constant fragment (Fc) region also reduces potential unwanted non-specific interactions during biochemical assays such as immunohistochemistry. Additionally, antibody fragments can reach 1/3 the size of whole IgG (50kDa vs 150kDa), making them useful in applications which require smaller targeting molecules to penetrate tissue or reduce steric hindrance. Antibody fragmentation provides a means of achieving antibody fragments from whole IgG by enzymatically digestion to produce either a Fab or a bivalent Fab, termed a F(ab')2, as described below.
IgG antibodies are immunoglobulin homodimers of heterodimers; they contain 2 heavy chains (50 kDa) each paired with a light chain (25 kDa). Heavy and light chains, as well as their dimerization, are stabilized through covalent disulfide bridges. Enzymatic cleavage of specific disulfide bonds results in fragments of differing composition.
The use of papain, an enzyme derived from papaya, results in reduction of exposed disulfide bonds in the hinge region of the antibody. This separation, or fragmentation, breaks the the antibody into three segments; 2 Fabs consisting of equal parts heavy chain and light chain, and 1 Fc region. Pepsin, another protease, preferentially digests the Fc region of the antibody, but leaves intact the hinge region, stabilizing the pairs of heavy and light chain regions that recognize antigen, resulting in bivalent Fabs or F(ab')2. Purification post-fragmentation is performed to remove unwanted Fc region, accomplished through protein A/G affinity or size exclusion chromatography.
Antibody fragmentation through enzymatic cleavage requires sufficient amounts of whole IgG. Although IgG is mostly uniform, fragmentation conditions for each antibody require optimization with initial pilot study analysis. Additionally, fragmentation reactions and purification have a typical yield of 40-60%. Should you require production of sufficient antibody quantities prior to fragmentation, our antibody manufacturing solutions pair effortlessly with antibody fragmentation.
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