Protein Band Smearing on Western Blot (Western Blot (CST Guide))

Question

Accepted Answer

Protein bands appear as vertical smears rather than discrete sharp bands. Smearing may occur above or below the expected molecular weight, making band interpretation difficult. Common causes: 1) Differential glycosylation: N-glycan or O-glycan modifications result in smear at higher than predicted molecular weights 2) Protein degradation: proteases create degradation products appearing as smear below expected molecular weight 3) Incomplete lysis without sonication: unsheared nuclear DNA interferes with SDS-PAGE gel loading and migration 4) Old lysate samples: degradation products accumulate even when stored at -80°C Solutions: 1) Treat samples with PNGase F enzyme to cleave N-glycans from glycoproteins; compare treated vs. untreated to confirm glycosylation-induced smearing 2) Add protease inhibitors: leupeptin (1.0 µg/ml) and PMSF to lysis buffer, or use Protease Inhibitor Cocktail (100X) #5871 3) Perform sonication: 3 × 10 second bursts with microtip probe sonicator at 15W (50% power) on ice to shear nuclear DNA 4) Use fresh lysate samples; store at -80°C for long-term storage and avoid repeated freeze-thaw cycles 5) Check PhosphoSitePlus for potential glycosylation sites on target protein