The adsorption and desorption of the giant heavily glycosylated protein mucin from solutions of different bulk concentrations have been followed at the nanometer scale using high resolution molecular microscopy based on optical waveguide lightmode spectroscopy. Modeling the layer as a uniaxial thin film allowed the in situ determination of adsorbed mass, mean layer thickness, and structural anisotropy. These parameters manifest highly significant adsorption-desorption hysteresis, indicating at least two dominant glycoprotein conformational types (i.e., molecular states, structurally and kinetically distinguishable). One of them is proposed to be a conformationally extended state that engenders uniaxial symmetry and dominates layers generated from low bulk concentrations. The revealed structure and the mechanism by which it is formed are postulated to be a general feature of the self-assembly of large glycoproteins. We expect that, inter alia, this knowledge will be relevant for understanding the extraordinary effectiveness of mucin thin films as boundary lubricants.