Carrier Proteins

Small molecules such as drugs, organic compounds, and peptides and oligosaccharides with a molecular weight of less than 2-5 kDa are not usually immunogenic, even when administered in the presence of adjuvant. In order to generate an immune response to these compounds, it is necessary to attach them to a protein or other compound, termed a carrier, that is immunogenic. When attached to a carrier protein the small molecule immunogen is called a hapten. Haptens are also conjugated to carrier proteins for use immunoassays. The carrier protein provides a means of attaching the hapten to a solid support such as a microtiter plate or nitrocellulose membrane. When attached to agarose they may be used for purification of the anti-hapten antibodies. They may also be used to create a multivalent antigen that will be able to form large antigen-antibody complexes. When choosing carrier proteins, remember that the animal will form antibodies to the carrier protein as well as to the attached hapten. It is therefore important to select a carrier protein for immunization that is unrelated to proteins that may be found in the assay sample. If haptens are being conjugated for both immunization and assay, the two carrier proteins should be as different as possible. This allows the antiserum to be used without having to isolate the anti-hapten antibodies from the anti-carrier antibodies.

One such example is keyhole limpet hemocyanin (KLH). KLH is a respiratory protein found in mollusks. Its large size makes it very immunogenic, and the large number of lysine residues available for conjugation make it very useful as a carrier for haptens. The phylogenic separation between mammals and mollusks increases the immunogenicity and reduces the risk of cross-reactivity between antibodies against the KLH carrier and naturally occurring proteins in mammalian samples. KLH is offered both in its native form, for conjugation via amines, and succinylated, for conjugation via carboxyl groups. Succinylated KLH may be conjugated to a hapten containing amine groups (such as a peptide) via cross-linking with carbodiimide between the newly introduced carboxyl groups of KLH and the amine groups of the hapten.

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H7017 Hemocyanin from Megathura crenulata (keyhole limpet)
H8283 Hemocyanin from Megathura crenulata (keyhole limpet) PBS solution
B8556 Hemocyanin from mollusk buffered aqueous solution
H9035 Hemocyanin from mollusk from Concholepas sp., buffered aqueous glycerol solution
H5654 Hemocyanin, succinylated from Megathura crenulata (keyhole limpet) lyophilized powder
B7542 Maleimide Activated BSA
K0383 Maleimide Activated KLH
T1001 Thyroglobulin from bovine thyroid powder, ≥90% (agarose gel electrophoresis)
T9145 Thyroglobulin from bovine thyroid (For Gel Filtration Chromatography)