Alterations in the Molecular Configuration of Mucin Glycoproteins Entail a Loss of Lubricity

Abstract Mucins, a family of glycoproteins, provide highly efficient lubrication on the eyes, in the mouth, and in the gastrointestinal tract of mammals. Although two key mechanisms responsible for the outstanding lubricity of mucin solutions, i.e ., sacrificial layer formation and hydration lubrication, have been identified, recent research indicates that the complex structure of mucins, e.g ., the presence of folded domains in the termini of the glycoproteins, might also be relevant for the tribological performance of mucin solutions. Here, we manipulate the molecular configuration of three different mucins ( i.e. , porcine gastric mucin MUC5AC, bovine submaxillary mucin MUC5B, and porcine intestinal mucin MUC2) by treating the glycoproteins either with the crosslinking agent glutaraldehyde (GA) or with the denaturing agent guanidine hydrochloride (Gua) and assess the ensuing consequences of those treatments. Although we observe a clear reduction in the lubricity of all mucin solutions upon treatment, neither mucin aggregation, nor a reduction of mucin hydration, nor an altered adsorption behavior of mucins to hydrophobic PDMS surfaces can account for this effect. Instead, we suggest that the treatments prevent the stretching of mucins and/or the unfolding of the mucin termini, and both processes may play an important role in retarding the force-induced desorption of mucins from surfaces as required for efficient hydration lubrication. Our results pinpoint molecular mechanisms which—to date—were not sufficiently considered for macromolecular lubricants. A better characterization of these molecular mechanisms will not only deepen our understanding of mucin-based lubricants but will also open the path for the development of more efficient, bio-inspired lubricants. Graphical abstract