Cleavage of IgG with proteases

When IgG molecules are treated with proteolytic enzymes (peptidases, proteases, proteinases) a limited proteolysis takes place, generating fragments that correspond to the different functional domains:
(click on the images below to see the model for each fragment)

Papain cleaves the heavy chains yielding three peptide fragments:

  • two Fab fragments (the name comes from fragment antigen binding; each separate Fab fragment is still capable of binding an antigen molecule);
  • and a single Fc fragment (from fragment crystallisable), since the two heavy chains remain bound through disulphide links.

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Papain: origin and applications

Papain

papaya (fruit)This enzyme can be extracted from the juice of the unripe fruit of papaya (Carica papaya).

It has application (can you imagine why?):

  • as meat tenderiser
  • in Medicine, as a digestive
  • to remove dead tissue in injuries (sores, ulcers, burns, surgical wounds, cysts,...): mixed with urea, in the form of an ointment for external use (commercial brands: Accuzyme, Ethezyme 830, Gladase, Kovia, Panafil, Ziox)
  • for clotting milk
  • in wool preparation
  • in pet food, to reduce viscosity and make it more pallatable
  • as an ingredient in cleansing solutions for soft contact lenses

If IgG is instead treated with pepsin, the cleavage points on the heavy chains are slightly different, giving:

  • a single fragment called F(ab')2 where the two Fab domains remain linked through the hinge region,
  • and another Fc' fragment, slightly different from the one obtained with papain (actually, this one is not obtained whole as shown here, but fragmented in several peptides, since pepsin has several targets on the H chain).

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Pepsin: origin and applications

Pepsin

gastric mucoseThis enzyme is synthesized by cells in the stomach lining and is secreted as a component of gastric juice.

Etimológicamente procede del griego pepsis, digestión.

Etymologically the name comes from the Greek pepsis, digestion.

It has application (can you imagine why?):

  • as a digestive (after purifying pepsin from pig or calf stomach)

The Fab, F(ab')2 and Fc fragments are useful in research and analytical laboratories.