Identification of a GM1‐Binding Protein on the Surface of Murine Neuroblastoma Cells

Abstract: S2OY murine neuroblastoma cells appear to express a protein component(s) able to adhere specifically to the oligosaccharide portion of GM1 (oligo‐GM1). To identify proteins with which the oligo‐GM1 becomes closely associated, a radiolabeled (¹²⁵I), photoactivatable derivative of oligo‐GM1 was prepared. This was accomplished by reductive amination of the glucosyl moiety of oligo‐GM1 to 1‐deoxy‐1‐aminoglucitol, followed by reaction of the amine with sulfosuccinimidyl 2‐(p‐azidosalicylamido)ethyl‐1,3′‐dithiopropionate (SASD). Crosslinking studies using the photoactivatable probe indicated that it came in close proximity to a protein with an apparent molecular mass of ∼ 71 kDa. In competition experiments, as little asa 10‐fold molar excess of oligo‐GM1 resulted in a selective reduction in labeling of this protein; preincubation with a 200‐fold molar excess of siayllactose was necessary to observe the same change in the labeling pattern, lending additional support to the hypothesis that the ∼ 71‐kDa protein specifically associates with oligo‐GM1. Cell surface location of the oligo‐GM1 binding protein was confirmed using subcellular fractionation and morphological analyses.