DEAE-cellulose, as an anion exchanger, preferentially binds proteins with a negative charge due to its positively charged functional groups. The correct answer is option 3.

Introduction

In protein purification, the DEAE cellulose anion exchanger plays a crucial role by selectively binding proteins based on their charge properties. This technique relies on electrostatic interactions where the positively charged resin attracts negatively charged biomolecules. Understanding this mechanism is essential for life sciences students preparing for exams in biochemistry and molecular biology.

Option Analysis

Each option represents a different protein charge scenario in ion-exchange chromatography.

• Option 1: No charge
  Proteins with no net charge (at their isoelectric point, pI) lack electrostatic attraction to the positively charged DEAE groups, so they do not bind and flow through the column.

• Option 2: Positive charge
  Positively charged proteins repel the positive charges on DEAE cellulose, preventing binding; these proteins typically pass unbound in the flow-through fraction.

• Option 3: Negative charge
  Negatively charged proteins (when buffer pH > protein pI) are strongly attracted to the protonated diethylaminoethyl (DEAE) groups on the cellulose matrix, enabling selective binding and purification.

• Option 4: Binding does not relate to charge
  Binding in anion exchange fundamentally depends on charge interactions; non-charge-based mechanisms apply to other chromatography types like size-exclusion.

Mechanism of DEAE Cellulose

DEAE cellulose features diethylaminoethyl groups attached to a cellulose backbone, which become protonated (positively charged) at neutral pH (typically pH 7-8). This weak anion exchanger operates via reversible ionic bonds with protein carboxylates or phosphates.

Proteins bind when their net charge is negative, controlled by buffer pH relative to the protein’s pI. Elution occurs by increasing salt concentration (e.g., NaCl gradient) or pH, disrupting interactions.

Applications in Protein Purification

DEAE cellulose excels in separating acidic proteins, nucleic acids, and enzymes from complex mixtures. Common in lab protocols for hemoglobin, albumin, or plasmid DNA isolation, it offers high capacity and biocompatibility.

For optimal results, start with low ionic strength buffers and scout pH 0.5-2 units above the target protein’s pI.​

Key Takeaway for Exams

Remember: Anion exchangers like DEAE cellulose bind negative charges (pH > pI); cation exchangers bind positive charges (pH < pI). This principle is frequently tested in GATE, CSIR NET, and biochemistry exams.​