Q.22 Papain digestion of IgG antibody molecule results into –

1. 2 Fab fragments and 1 Fc fragment
2. 2 Fc fragments and 1 Fab fragment
3. 4 Fab fragments and 2 Fc fragments

4. Papain digestion of IgG produces 2 Fab fragments and 1 Fc fragment. This is the correct answer for the multiple-choice question, as confirmed by standard immunology principles.

   Question Breakdown

   Papain is a cysteine protease from papaya that cleaves IgG antibodies above the hinge region in the heavy chains, after disulfide bonds. This action separates the Y-shaped IgG into its functional parts without further degrading the Fc portion.

   Option Analysis

   • 2 Fab fragments and 1 Fc fragment: Correct. Each Fab (50 kDa) includes one light chain and the VH-CH1 of one heavy chain for antigen binding. The Fc (50 kDa) comprises CH2-CH3 from both heavy chains for effector functions like complement activation.

   • 2 Fc fragments and 1 Fab fragment: Incorrect. Papain yields only one intact Fc from the paired heavy chain constant regions; it does not split into two Fc pieces.​

   • 4 Fab fragments and 2 Fc fragments: Incorrect. IgG has just two Fab arms; over-digestion might fragment further, but standard papain digestion stops at two Fab and one Fc.

   • 1 Fab and 1 Fc fragment: Incorrect. Cleavage symmetrically produces two identical Fab fragments from the two arms of the IgG molecule.​1 Fab and 1 Fc fragment

   Introduction to Papain Digestion of IgG Antibody

   Papain digestion of IgG antibody is a key technique in immunology, where the enzyme papain cleaves the antibody above its hinge region. This process generates 2 Fab fragments and 1 Fc fragment, essential for research and therapeutics. Ideal for GATE Life Sciences prep, this breakdown covers mechanisms, results, and applications.

   IgG Structure Basics

   IgG, the most common antibody, forms a Y-shape with two heavy chains and two light chains linked by disulfide bonds. The Fab regions at the tips bind antigens, while the Fc stem handles immune effector functions.​

   How Papain Digestion Works

   Papain requires a reducing agent like cysteine and cleaves peptide bonds above the hinge region’s disulfide bonds. This yields:

   • Two Fab fragments (~50 kDa each), retaining antigen-binding sites.

   • One Fc fragment (~50 kDa), from the dimerized heavy chain constants.

   ​
   Diagram showing papain cleavage sites on IgG, producing 2 Fab and 1 Fc.​

   Why Other Digestion Results Differ

   Pepsin digestion below the hinge gives F(ab’)2 (two linked Fab) and pFc’. Papain uniquely preserves the intact Fc, unlike harsher proteases.​

   Applications in Research

   Fab fragments enable better tissue penetration for diagnostics and drugs, avoiding Fc-mediated effects. Fc is used in crystallography and receptor studies.

   GATE Exam Relevance

   This topic tests antibody structure-function knowledge. Memorize: papain = 2 Fab + 1 Fc for quick MCQ solves.​