Analysis of Typical Difficulties in Separation and Purification of Natural Proteins: Optimization Schemes Based on Ion Exchange Chromatography and Size Exclusion Chromatography

一、Common Purification Problems, Causes and Countermeasures

Problem 1: Sample rushes through with negligible protein binding

Causes: 

Incorrect buffer pH: pH near the protein’s pI reduces net charge, negating electrostatic attraction against charge stationary phases.

Sample ionic strength too high: Salt can compete for binding and reduces electrostatic interactions.

Wrong medium type: Oppositely charged proteins will not bind to resins due to electrostatic repulsion.

Solutions:

Buffer pH should be 0.5–1.5 units above the protein’s pI for anion exchange (Q/DEAE) columns or 0.5–1.5 units below the protein’s pI for cation exchange (SP/CM) columns to ensure enough surface charge.

Sample should be desalted using dialysis or ultrafiltration so that its conductivity is<5 ms="">

Sample should be run on appropriate media. Acidic proteins should be run on anion exchangers, while basic proteins should be run on cation exchangers.

Problem 2: Very poor recovery of protein; protein of interest binds very tightly and cannot be eluted

Causes: 

Too strong of an electrostatic interaction, too shallow of a salt gradient, too low of a maximum elution salt concentration, slight change in pH causing change in protein charge, and cooperative hydrophobic adsorption within the resin pore ^[2].

Solutions:

Use linear NaCl gradients up to 0.8–1 mol/ L with low flow rates of 0.5–1 column volumes/hr.

Use buffer pH slightly above or below the protein’s pI to decrease electrostatic interactions.

Include 0.01% Tween-20 (nonionic detergent) in the elution buffer to help decrease hydrophobic co-adsorption.

Tips:

Observe the column absorbance at 280 nm during elution. Fractionate eluate separately and analyze the protein profile by SDS- PAGE.

Problem 3: Tailing peaks and overlapping impurity signals during SEC, poor separation resolution

Causes:

Mismatched resin pore size: Protein molecular weight falls at the edge of the resin’s fractionation range.

Overloaded sample volume (exceeding 5% of column volume).

Excess flow rate prevents full diffusion and partition inside gel pores.

Protein aggregation creates larger oligomers with altered hydrodynamic radii.

Solutions:

Select resins by molecular weight: Superdex 200 (>100 kDa), Superdex 75 (20–100 kDa), G-75/G-15 (small proteins).

Concentrate samples and limit injection volume to 2%–5% column volume.

Reduce flow rate to 0.3–0.5 mL/min to extend diffusion equilibrium time.

Run SEC at low temperature with reducing agents and protease inhibitors to suppress aggregation and degradation.

Application Positioning:

SEC serves as the final polishing step to remove aggregates, degraded fragments and small-molecule impurities, improving monomer homogeneity.

Problem 4: Severe activity loss and degraded bands after complete purification

Causes:

High operating temperature during lysis and chromatography, persistent hydrolysis by endogenous proteases, extreme pH or salt disrupting spatial conformation, and abrupt buffer changes between IEX and SEC steps.

Solutions:

Perform all steps at 4 °C and add broad-spectrum protease inhibitor cocktails to lysis, equilibration and elution buffers.

Maintain buffer pH within the protein’s stable range and avoid extreme acid or alkaline environments.

Desalt IEX eluates via ultrafiltration to match SEC buffer and prevent dramatic osmotic shocks.

Problem 5: Unsatisfactory overall purity after serial IEX and SEC purification

Causes:

Target and contaminating proteins possess highly similar charge and molecular weight; unfiltered particulate impurities clog resin pores before loading.

Solutions:

Refine IEX salt gradients and collect target peaks in segmented fractions to boost resolution.

Insert ammonium sulfate precipitation or hydrophobic interaction chromatography as intermediate polishing steps between IEX and SEC.

Remove particulate debris via depth filtration and high-speed centrifugation before sample loading to protect column bed integrity^[3].

二、Purification Services and Technical Advantages of Camede Biotech

1.Customized Process Design

Engineers design tailored workflows: crude treatment → IEX capture → SEC polishing. For large proteins, multi-stage SEC is prioritized for impurity clearance; small proteins undergo preliminary IEX fractionation before fine SEC separation to fit all molecular weight ranges.

2. Complete Chromatography Hardware Support

Fully automated AKTA purification systems are equipped with a full portfolio of anion/cation exchange media (Q, SP, DEAE, CM) and SEC resins (Superdex 75/200, Sephacryl S). Flexible medium combinations resolve weak binding and low resolution issues.

3.Full-process Quality Control and Activity Protection

Low-temperature operations and dedicated inhibitor cocktails are applied from sample pretreatment. All pH, salt gradient and flow rate parameters are precisely controlled. Post-purification tests including SDS-PAGE, SEC-HPLC and activity assays generate complete test reports. Delivered protein purity can exceed 95% with intact biological activity retained.

4.Flexible Service Modes

Clients may purchase full-turnkey purification or individual modules including IEX optimization, SEC polishing and sample pretreatment. For proteins with unknown physicochemical properties, small-scale trials identify optimal parameters before scale-up to cut experimental costs.

5.Rich Experience with Challenging Samples

The team has extensive experience purifying low-abundance, aggregation-prone and membrane-bound natural proteins, effectively resolving common industrial bottlenecks such as insufficient IEX adsorption and overlapping SEC peaks.

Reference

[1] Wu M, et al. Isolation and purification of immunoglobulin G from bovine colostrums by hydrophobic charge-induction chromatography[J]. Journal of Dairy Science, 2015,98(5):2973-2981

[2] 王启迪，全灿，周俊波。蛋白质纯化技术研究进展 [J]. 现代生物医学进展，2017,17 (32):6374-6379.

[3] Fekete S, et al. Hydrophobic interaction chromatography for the characterization of monoclonal antibodies and related products[J]. Journal of Pharmaceutical and Biomedical Analysis, 2016,130:3-18.