Single-chain variable fragment
Fragment / From Wikipedia, the free encyclopedia
A single-chain variable fragment (scFv) is not actually a fragment of an antibody, but instead is a fusion protein of the variable regions of the heavy (VH) and light chains (VL) of immunoglobulins, connected with a short linker peptide of ten to about 25 amino acids.[1] The linker is usually rich in glycine for flexibility, as well as serine or threonine for solubility, and can either connect the N-terminus of the VH with the C-terminus of the VL, or vice versa.[2] This protein retains the specificity of the original immunoglobulin, despite removal of the constant regions and the introduction of the linker.[3] The image to the right shows how this modification usually leaves the specificity unaltered.
![Thumb image](http://upload.wikimedia.org/wikipedia/commons/thumb/0/04/ScFv-rotation.gif/300px-ScFv-rotation.gif)
![Thumb image](http://upload.wikimedia.org/wikipedia/commons/thumb/f/f8/Single_chain_variable_fragment.svg/220px-Single_chain_variable_fragment.svg.png)
These molecules were created to facilitate phage display, where it is highly convenient to express the antigen-binding domain as a single peptide. As an alternative, 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 (chimeric antigen receptor).
Unlike monoclonal antibodies, which are often produced in mammalian cell cultures, scFvs are more often produced in bacteria cell cultures such as E. coli.[3]