Common Protectants and Formulations for Protein Storage

Proteins face major risks during storage: surface adsorption and aggregation, conformational denaturation, chemical degradation (oxidation/hydrolysis/deamidation), and microbial contamination. Choosing an appropriate buffer system and protectants, together with suitable temperature and aliquoting strategies, can markedly extend stability and preserve activity.

I. Preventing surface adsorption and aggregation

Proteins at low concentration readily adsorb to container walls (e.g., microtubes, glassware), lowering recovery; at high concentration, stronger intermolecular interactions favor aggregation and precipitation.

1.Inert proteins

Bovine serum albumin (BSA)

For low-concentration proteins (typically <1 mg/mL) prone to wall adsorption, let BSA adsorb first to protect the target protein. Commonly 0.01%–0.1% (w/v), occasionally up to 0.5%. May interfere with mass spectrometry and immunoassays (cross-reactivity/background) and with Bradford quantification; BSA can bind hydrophobic ligands and metal ions, potentially affecting some functional assays.

Casein

Commonly used to block nonspecific binding in immunoassay systems; likewise may interfere with downstream immunoassay quantitation.

2.Nonionic surfactants

​Tween-20、Triton X-100

Coat hydrophobic interfaces and reduce conformational disturbance and aggregation at the air–liquid/container wall, especially effective for membrane or hydrophobic proteins. Typically 0.005%–0.1% (v/v); a common starting point is 0.01%. May alter enzyme activity or affect certain binding/separation steps; Triton is a stronger detergent than Tween—pilot tests recommended.

​Poloxamers(e.g., Pluronic F-68)

Sometimes gentler under shear/stirring/freeze–thaw stress; an alternative option.

II. Maintaining structural stability (anti-denaturation)

These reagents stabilize the native conformation and prevent unfolding.

1.Polyols and sugars

​Glycerol

Preferential exclusion/solvent effects stabilize folding; lowers freezing point and reduces ice damage. Typically 10%–50% (v/v). At 50%, solutions are not fully frozen at −20 °C, suitable for “partial-freeze” storage to avoid repeated freeze–thaw. Increases viscosity and may slightly affect enzymatic rates and spectrophotometry; high concentrations impede pipetting.

​Sucrose, trehalose

Preferential exclusion/vitrification; widely used for lyophilization and −80 °C storage. Generally 2%–10% (w/v); higher for lyophiles. Prefer nonreducing sugars (sucrose, trehalose); avoid reducing sugars (e.g., glucose) for long-term aqueous storage to prevent glycation.

2.Amino acids and amines

​Glycine, proline, arginine·HCl, taurine

Improve solubility; suppress aggregation or off-pathway interactions of folding intermediates. Commonly 50–500 mM, to be screened per protein. High arginine can sometimes reduce stability or affect activity—optimize case-by-case.

III. Preventing chemical degradation

Proteins may undergo oxidation, hydrolysis, or deamidation.

1.Reducing agents (prevent incorrect disulfides and oxidation)

​DTT

Potent and common, but auto-oxidizes in air, especially at pH > 7, with a short half-life. Prepare fresh or replenish regularly; typically 0.1–5 mM.

​β-ME

Strong odor and volatility; weaker than DTT and now largely replaced.

​TCEP

More oxygen-stable and broadly pH-compatible; a better long-acting choice for many systems. Will continuously reduce disulfides; if a protein’s structure/function depends on native disulfides, long-term coexistence with TCEP may disrupt the native state. TCEP can interfere with thiol–maleimide conjugation; compatibility issues exist with certain metals/nucleophiles—confirm downstream needs.

2.Metal chelators (prevent metal-ion–catalyzed oxidation)

EDTA(commonly 0.1–2 mM)

Chelates trace Fe/Cu, reducing Fenton-type reactions. Not recommended for metalloproteins/metal cofactor–dependent enzymes (e.g., zinc proteins, Mg²⁺-dependent complexes); may affect subsequent Ni–NTA purification of His-tag proteins.

3.Protease inhibitors

Broad-spectrum cocktails (e.g., containing AEBSF, aprotinin, leupeptin, pepstatin, E-64, bestatin, etc.)

Use when protease contamination is possible, especially in cell/tissue lysates. Some inhibitors are irreversible or interfere with downstream enzymology; EDTA-containing mixes affect metalloproteins/metal-affinity chromatography. For purified recombinant proteins from clean sources, long-term inclusion is usually unnecessary.

4.Antimicrobials

Sodium azide (NaN₃, 0.02%–0.05% w/v)

Common for short-term storage at 4 °C. Highly toxic; prohibited in cell/in vivo experiments; inhibits HRP and other heme enzymes; can form metal azides in plumbing (explosive risk); handle and dispose properly.

Thimerosal

Historically used in some antibody solutions; mercury compounds pose safety/compliance risks and are largely replaced by safer options.

IV. Buffer systems (maintaining pH)

1.Common buffers: Tris-HCl, PBS (phosphate-buffered saline), HEPES, MOPS, etc.

2.Selection principles: pKa within ±1 of the target pH; consider temperature sensitivity and compatibility with salts/metal ions.

• ​Tris: pH varies significantly with temperature (about −0.028 pH/°C); low temperatures/freezing can cause actual pH drift.
• ​PBS: Incompatible with high concentrations of divalent cations (Ca²⁺/Mg²⁺) or systems prone to precipitation; may affect metal-affinity steps such as Ni–NTA.
• ​HEPES: Better temperature stability than Tris; often used at 4 °C or room temperature.

V. Recommended base formulation

20–50 mM Tris-HCl, pH 8.0 (buffer system)

150 mM NaCl (provides ionic strength, approximates physiological conditions)

10% (v/v) glycerol (stabilizes structure and protects against freezing)

1 mM EDTA (prevents metal-catalyzed oxidation)

0.5 mM TCEP (prevents oxidation; more stable than DTT)

0.02% NaN₃ (antimicrobial, if needed)

VI. Storage strategies

①High-concentration storage: Moderately increasing protein concentration generally improves stability; concentrate first, then aliquot.

②Aliquot management: Regardless of temperature, always aliquot into small volumes to avoid repeated freeze–thaw.

③Storage temperature options:

• 4 °C: For short-term (days to weeks); consider adding a preservative/biocide.
• −20 °C: Common; add 20%–50% (v/v) glycerol to mitigate freeze–thaw and ice-crystal damage.
• −80 °C: Preferred for long-term storage; glycerol optional, but aliquoting is mandatory.
• Liquid nitrogen/vapor phase: For highly precious samples; enables near-“glassy” preservation.
• Lyophilization: Offers the longest stability; pair with sucrose, trehalose as protectants.

Aladdin: https://www.aladdinsci.com/