Dextran: Multifunctional polysaccharides for biology and medicine
Product Manager：Harrison Michael
Dextrans are polysaccharides with molecular weights starting at 1,000 Daltons, consisting of a linear backbone of α-linked D-glucopyranosyl units. Their unique structural properties and versatility make them essential in various biological and medical research applications.
I. Structural Characteristics of Dextrans
Dextrans are categorized into three main types based on their structural features:
1. Class 1 Dextrans: These have an α(1→6)-linked D-glucopyranosyl backbone with side branches linked by α(1→2), α(1→3), or α(1→4) bonds. The exact structure depends on the microbial strains and cultivation conditions used in their production.
2. Class 2 Dextrans (Alternans): Characterized by alternating α(1→3) and α(1→6)-linked D-glucopyranosyl units with α(1→3)-linked branches.
3. Class 3 Dextrans (Mutans): These have a backbone of consecutive α(1→3)-linked D-glucopyranosyl units with α(1→6)-linked branches.
Advanced NMR spectroscopy techniques are crucial for the detailed structural analysis of these dextrans.
II. Synthesis and Sources of Dextrans
Dextrans are synthesized by various bacteria, including beneficial lactic acid bacteria like Leuconostoc mesenteroides and Lactobacillus brevis, as well as dental plaque-forming Streptococcus mutans. These bacteria produce dextrans from sucrose through dextransucrase enzymes that catalyze the polymerization of glucose residues.
Optimizing the biosynthesis process is essential for enhancing dextran production for industrial and research applications.
III. Functional Roles in Microbial Systems
Dextrans play a critical role in bacterial adhesion and biofilm formation. They help bacteria modulate their cell surface properties, which can be adjusted based on the polysaccharide's rigidity and environmental factors like pH and ionic strength. At low salt conditions, rigid polysaccharides with a softer surface result in low bacterial adhesion, whereas more flexible polysaccharides with a rigid surface lead to higher adhesion.
The elasticity of dextrans, influenced by the pyranose ring structure, is vital for structural integrity. The glucopyranose ring transitions from a chair-like to a boat-like conformation under force, allowing dextrans to handle mechanical stress and modulate ligand binding in biological systems.
IV. Physical and Chemical Properties
Purified dextrans, depending on microbial strains and production methods, are white, tasteless solids with high water solubility. Their solutions behave as Newtonian fluids, with viscosity influenced by concentration, temperature, and molecular weight distribution.
Understanding these properties is crucial for developing dextran-based products in pharmaceuticals, cosmetics, and other industries requiring precise viscosity control.
Dextrans have a long history of safety and are used as additives in food and chemicals, as well as in pharmaceutical and cosmetics manufacturing. They are investigated for targeted and sustained delivery of drugs, proteins, enzymes, and imaging agents. Clinically, dextrans with a molecular weight range of 75-100 kDa are used as blood-plasma volume expanders in transfusions. Other applications include using dextrans with polyethylene glycol in aqueous two-phase systems for biochemical extraction. The hydroxyl groups in dextran offer many sites for derivatization, creating a largely unexplored class of biocompatible and environmentally safe compounds.
Cross-linked dextran beads are widely used in chromatography in biochemical research and industry. The classic application of cross-linked dextrans is as gel filtration media in packed-bed columns for separating and purifying biomolecules with molecular weights ranging from 0.7-200 kDa. Ion exchange chromatography also utilizes dextran derivatized with positively or negatively charged moieties such as carboxymethyl (CM), diethylaminoethyl (DEAE), diethyl(2-hydroxypropyl) aminoethyl (QAE), and sulfopropyl (SP).
V. Biological Functions and Roles of Dextrans
Dextrans significantly influence bacterial adhesion and biofilm formation, which are crucial for both beneficial and pathogenic interactions. Their secretion allows bacteria to adjust their cell surface properties, affecting adhesion and biofilm stability. The structural integrity and elasticity of dextrans are key factors in these processes. The transition of the glucopyranose ring from a chair-like to a boat-like conformation under mechanical stress enables dextrans to accommodate various biological functions.
VI. Medical and Experimental Applications of Dextrans
Drug Delivery Systems
Dextrans are widely used in drug delivery systems due to their biocompatibility and ability to form stable complexes with various drugs. Conjugating drugs with dextran can enhance stability, bioavailability, and controlled release of therapeutic agents. This is particularly important in targeted drug delivery, where dextran-based nanoparticles can reduce side effects and improve treatment efficacy.
Blood-Plasma Volume Expanders
In clinical settings, dextrans with molecular weights of 75-100 kDa are used as blood-plasma volume expanders. These dextrans help maintain blood pressure and volume in patients experiencing significant blood loss or shock, thanks to their high water solubility and appropriate rheological properties.
Tissue Engineering and Wound Healing
Recent advancements have explored using dextran hydrogels in tissue engineering and wound healing. Due to their biocompatibility and ability to form biodegradable matrices, dextran hydrogels provide a conducive environment for cell development and tissue regeneration. These hydrogels can be tailored to deliver development factors and other therapeutic agents, enhancing the healing process.
Chromatography and Biochemical Research
Cross-linked dextran beads are extensively used in chromatography for separating and purifying biomolecules. These beads serve as gel filtration media in packed-bed columns, allowing the separation of molecules based on size. Ion exchange chromatography also employs dextran derivatized with charged moieties, enabling the efficient separation of proteins, nucleic acids, and other biomolecules.
Research on Bacterial Adhesion and Biofilms
Dextrans are vital in studying bacterial adhesion and biofilm formation. Understanding how dextrans modulate bacterial surface properties and adhesion mechanisms can help develop strategies to prevent and control biofilm-related infections. This knowledge is particularly relevant in dental research, where dextran-producing bacteria like Streptococcus mutans play a significant role in tooth decay.
Conclusion
Dextrans are versatile polysaccharides with crucial roles in biological and medical research. Their unique structural properties and functional versatility make them invaluable in a wide array of applications, from drug delivery systems and clinical therapies to tissue engineering and biochemical research. Ongoing advancements continue to expand the potential uses of dextrans, underscoring their importance as a multifunctional biomaterial in science and medicine.
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