# DBT JRF 2022 — Question 65

Exam: DBT JRF 2022 · Section: B · Topic: Immunology › Antibody Purification - Protein A · Difficulty: Medium

## Question

Protein A used for the purification of IgG is isolated from:

## Options

- **A.** Staphylococcus aureus
- **B.** Streptomyces lividans
- **C.** Streptomyces pyogenes
- **D.** Staphylococcus carnosus

## Answer

Option A

## Explanation

Protein A from Staphylococcus aureus — IgG purification: Protein A is a surface protein from S. aureus cell wall that has an extraordinary property: • Binds with very high affinity to the Fc region of IgG antibodies from many mammalian species (especially human, mouse, rabbit IgG). • Binding is through the CH2-CH3 hinge region of the Fc portion. Application in antibody purification: • Protein A-Sepharose affinity columns are the gold standard for purifying IgG. • Crude serum/culture supernatant is loaded → IgG binds to Protein A → contaminants washed away → IgG eluted with low pH buffer (pH 2.5–3.0) or high salt. • Achieves >95% purity in one step. Note: Protein G (from Streptococcus) also binds Fc but with slightly different species specificity. Answer: Protein A (from S. aureus) binds the Fc region of IgG; used for one-step IgG affinity purification.

Source: https://mypyqbuddy.com/questions/protein-a-used-for-the-purification-of-igg-6a104cd5920734408bc0c750