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.