Protein blotting: detection of proteins with colloidal gold, and of glycoproteins and lectins with biotin-conjugated and enzyme probes

Abstract

Methods to detect "native" proteins immobilized on nitrocellulose membranes in spot tests or on blots prepared from polyacrylamide slab gels after electrophoretic separation are described. Gold sols were found to be useful as general stains for proteins: They are polychromatic, yield an indelible record, and are complementary to india ink as protein stains because these two stains have different sensitivities for a number of proteins tested. For detection of wheat germ lectin (WGL)-binding glycoproteins, avidin-peroxidase was an effective enzyme probe, because the glycoportion of the avidin moiety possesses binding affinity to WGL. Glycocomponents in human parotid saliva were detected with this probe and with the following biotin-conjugated lectins as intermediary probes: soybean lectin, Bandeiraea simplicifolia lectin, Lotus tetragonolobus lectin, and kidney bean lectin. Autoclaving blots prior to probing eliminated endogenous peroxidase activity. Concanavalin A and WGL were separated by isoelectric focusing and detected on blots with horseradish peroxidase and avidin-peroxidase, respectively. The versatility of the biotin/avidin system was used to detect other lectins on similar blots using biotin-conjugated glycoproteins as intermediary probes: Helix pomatia lectin and B. simplicifolia lectin were detected with biotinyl neoglycoproteins, and kidney bean lectin with biotin-conjugated components of parotid saliva.