Related Experiment Video
Updated: Aug 15, 2026

Using Scaffold Liposomes to Reconstitute Lipid-proximal Protein-protein Interactions In Vitro
Published on: January 11, 2017
Human tear viscosity: an interactive role for proteins and lipids
Scott M Gouveia1, John M Tiffany
1Nuffield Laboratory of Ophthalmology, University of Oxford, Oxford, OX2 6AW, UK.
Abstract:
Human tear viscosity is poorly understood. Tears need to remain on the ocular surface for lubrication without causing damage to the surface epithelia due to drag when blinking. Whole tears are shear-thinning (non-Newtonian), which cannot be explained by the amount of mucin present, nor by individual proteins. Whole tears minus lipids become Newtonian. Though no free lipids had previously been found in collected tears, tear lipocalin (TL), a major tear protein, is known to bind lipids. In this study, we aimed to confirm whether there are any free lipids in collected tears, and to clarify the combined contribution of tear proteins to viscosity, including experiments on recombinant TL, both without (apo-TL) and with (holo-TL) bound lipid. We also investigated possible oligomer formation by holo- and apo-TL as a mechanism for viscosity using SDS-PAGE and analytical ultracentrifugation (AU). For comparison, we have included results for beta-lactoglobulin, a well-characterised lipocalin protein. No free lipids were detected in whole tears. Rheology showed that any protein combination that included lysozyme or lactoferrin was shear-thinning, as was apo-TL, though holo-TL was Newtonian (linear). Results from SDS-PAGE and AU showed apo-TL to be entirely monomeric, but holo-TL showed some dimerization. Both apo- and holo-beta-lactoglobulin exhibited a monomer-dimer equilibrium. We conclude that hetero-protein interactions, possibly electrostatic, involving lipid-binding-induced structural changes to TL, significantly contribute to the viscosity of human tears.
More Related Videos
08:50The Mechanics of (Poro-)Elastic Contractile Actomyosin Networks As a Model System of the Cell Cytoskeleton
Published on: March 10, 2023
09:29Obtention of Giant Unilamellar Hybrid Vesicles by Electroformation and Measurement of their Mechanical Properties by Micropipette Aspiration
Published on: January 19, 2020
Related Concept Videos
Membrane Fluidity
Mosaic nature of the membrane
The mosaic characteristic of the membrane helps the plasma membrane remain fluid. The integral proteins and lipids exist as separate but loosely-attached molecules in the membrane. The membrane is a relatively...
Membrane Fluidity
Fluid Mosaic Model
Viscosity
The SI unit of viscosity is...
Mechanical Protein Functions
Protein Diffusion in the Membrane