Biotin-dPEG®₄-hydrazide

Biotin-dPEG®4-hydrazide, product number 10219, is a popular offering from Quanta BioDesign, Ltd. The amphiphilic spacer provides excellent water solubility for the biotin group. The water-soluble dPEG®4 spacer is longer than the hydrophobic aminocaproic acid (LC) spacer used in biotin-LC-hydrazide. Moreover, the dPEG®4 spacer reduces or eliminates non-specific binding in many applications.
Conventional Biotinylation Reagents Compared to Biotin-dPEG®4-hydrazide

Biotinylation is the process of covalently attaching biotin to a molecule such as a peptide, protein, or nucleic acid, or a surface such as glass or gold. Bioconjugation research and product development use biotin extensively. Biotin is poorly soluble in water. However, the amphiphilic dPEG® linker imparts excellent solubility in aqueous media and organic solvents. Traditionally, biotin-hydrazide reagents add the hydrazide moiety directly onto the carboxylic acid end of either biotin or LC-biotin (biotin coupled to aminocaproic acid). These constructs are quite hydrophobic. Therefore, dissolution in an organic solvent (typically DMSO) is required to use them. Their hydrophobic nature can trigger rapid aggregation of biotinylated molecules, especially proteins.

The dPEG®4 spacer in Biotin-dPEG®4-hydrazide is amphiphilic. The ability to use Biotin-dPEG®4-hydrazide directly in water or aqueous buffer makes it more compatible with biological molecules than LC-biotin. Also, this product will not trigger aggregation due to hydrophobicity issues. Indeed, it reduces non-specific binding between biotin and biomacromolecules. A crosslinker's hydrophobicity often triggers non-specific binding.
Using Biotin-dPEG®4-hydrazide in Bioconjugation
Biotin-dPEG®4-hydrazide is a carbonyl-reactive compound that forms semi-permanent hydrazone bonds with aldehydes, ketones, and carboxylic acid groups. Although there are numerous natural small molecules containing aldehydes and ketones, macromolecules of biological importance (peptides, proteins, and nucleic acids) rarely contain them. However, glycosylated proteins such as antibodies frequently contain carbohydrate residues known as reducing sugars that can be oxidized with sodium periodate, neuraminidase, or galactose oxidase to form aldehydes.

The aldehydes thus formed then can be reacted with Biotin-dPEG®4-hydrazide at pH 6.0 – 6.0, labeling the protein with biotin through the formation of a Schiff base. Aniline or para-phenylenediamine catalyzes the reaction, forming the Schiff base quickly. For additional bond stability, sodium cyanoborohydride can be used to reduce the Schiff base to a secondary amine. Via carbodiimide chemistry (for example, 1-Ethyl-3-(3-dimethylaminopropyl)carbodiimide, also known as EDC), Biotin-dPEG®4-hydrazide reacts with carboxylic acid groups forming a stable bond.

Biotin-dPEG®4-hydrazide is highly useful for installing a biotin label onto glycoproteins. It is also used in cell labeling to label glycoproteins on cell surfaces. Biotinylated glycoproteins can be identified using streptavidin-horseradish peroxidase (HRP) conjugates, because of the high affinity between biotin and streptavidin. Biotinylated secondary antibodies are used frequently with streptavidin in plate-based assays such as ELISA and western blots. This reagent, coupled with avidin that has been modified to have reduced biotin-binding affinity, is for affinity purification of molecules.
Oxyamine Alternatives to Biotin-dPEG®4-hydrazide
Compounds functionalized with oxyamine also form bonds with aldehydes and ketones. These bonds are called "oxime bonds." Oxime bonds are more stable than hydrazone bonds at low pH. Consequently, biotin functionalized with oxyamine may be preferable to Biotin-dPEG®4-hydrazide in some applications. Quanta BioDesign offers products with the oxyamine functional group as an alternative to Biotin-dPEG®4-hydrazide.

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