Single chain variable fragment

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RasMol rendering of the structure of an immunoglobulin.

Rotating scFv fragment with highlighted complementatity determining regions (CDRs).

Single Chain Variable Fragment (scFv) is a fusion of the variable regions of the heavy and light chains of immunoglobulins, linked together with a short (usually serine, glycine) linker. This chimeric molecule retains the specificity of the original immunoglobulin, despite removal of the constant regions and the introduction of a linker peptide. The image to the right shows how this modification usually leaves the specificity unaltered. These molecules were created historically to facilitate phage display where it is highly convenient to express the antigen binding domain as a single peptide. Alternatively, scFv can be created directly from subcloned heavy and light chains derived from a hybridoma. scFvs have many uses - e.g. flow cytometry, immunohistochemistry and as antigen binding domains of artificial T cell receptors.

[edit] scFv Purification

Single chain variable fragments lack the constant Fc region found in complete antibody molecules, and thus, the common binding sites (e.g. Protein A/G) used to purify antibodies. These fragments can often be purified/immobilized using Protein L since Protein L interacts with the variable region of kappa light chains.

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