Direct visualization of colloidal gold‐bound molecules and a cell‐surface receptor by ultrahigh‐resolution scanning electron microscopy

Abstract
The structure of protein A‐coated colloidal gold particles, and of macrophage cell‐surface receptors conjugated with immunogold particles, was studied using an ultrahigh‐resolution scanning electron microscope. Protein A, when conjugated with 15‐nm gold, formed a coat completely surrounding the particle. Particles conjugated with both protein A and immunoglobulin G (IgG) were similar, but with additional protrusions formed by the IgG. IgG molecules directly bound to gold were resolved sometimes as complexes of three units, sometimes as more filamentous, V‐shaped structures. On the cell surface of a macrophage reacted with a monoclonal antibody to Mac‐1 antigen (the murine C3bi receptor) followed by protein A‐gold, gold particles were seen to be linked via the IgG to the receptor, visualized as a round granule.

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