An eastern blot is an analytical technique used to detect post‑translational modifications on proteins, such as carbohydrate or lipid moieties, after they have been separated by gel electrophoresis and transferred to a membrane.
Explanation
Eastern blotting is conceptually similar to the western blot but focuses on identifying covalent modifications rather than the polypeptide backbone itself. Proteins are first separated by sodium dodecyl sulphate‑polyacrylamide gel electrophoresis or two‑dimensional electrophoresis and then transferred onto nitrocellulose or polyvinylidene fluoride membranes. Instead of probing with antibodies against protein epitopes, the membrane is incubated with reagents that bind specific modifications: lectins recognize particular sugar motifs, antibodies can target glycan epitopes, and hydrophobic stains or antibodies can detect lipidation. Detection can involve enzyme‑linked or fluorescent labels, similar to western blots. Variations include the eastern‑western blot, which sequentially probes for both modifications and the protein backbone, and far‑eastern blotting, which separates lipids by thin‑layer chromatography before transfer to membranes. Eastern blotting is valuable for mapping glycosylation patterns, characterizing lipoproteins, validating recombinant protein modifications and studying disease‑associated alterations in glycan structures. Because glycosylation is highly heterogeneous, careful choice of lectins and controls is needed.
Applications and examples
Eastern blotting has been used to examine glycosylation of immunoglobulins by probing transferred proteins with concanavalin A or wheat germ agglutinin. Viral glycoproteins such as influenza haemagglutinin and HIV gp120 can be assessed for appropriate glycan trimming using panels of lectins. Far‑eastern blotting allows visualization of glycolipids extracted from tissues; for example, gangliosides separated by thin‑layer chromatography can be transferred to membranes and detected with cholera toxin B subunit. Detection of lipid modifications on small GTPases such as Ras can be achieved with antibodies that recognize farnesylated or geranylgeranylated forms. Another variation uses Pro‑Q Emerald dye to stain periodate‑oxidized glycans on blotted proteins.
Eastern blot and related methods expand the immunoblot toolbox to encompass not only protein abundance but also critical post‑translational modifications. Mapping these modifications provides insights into protein function, quality control and disease mechanisms.
Related Terms: Western blot, Glycosylation, Lectin, Lipidation, Far‑eastern blot