VMC 221: Veterinary Immunology and Serology (1+1)

HINGE REGION

• Fab regions of immunoglobulin which bind antigen can swing around central molecule and it is possible as they are hinged.
• The hinge region is about 12 amino acid long and located between C_H1 and C_H2 and the sequence is unique for each immunoglobulin class and subclass. But the μ and ε heavy chains do not have hinge region.
• The hinge region of IgD lack in cysteine residue thus there is no inter chain links.
• This region is hydrophilic and rich in proline residues.
• When digested with proteolytic enzyme papain, it cleaves at hinge region by hydrolysis of peptide bonds and produce 3 fragments, 2 ‘Fab’ fragments (sedimentation coefficient is 3.5S) and one F_C fragment.
• When digested with pepsin, the site of cleavage is towards carboxy terminal side of disulphide bond and produce two Fab fragments held together [referred as F(ab) ₂] with sedimentation coefficient of 5S and F_C fragment is digested into multiple fragments.