Molecular aspects of boundary lubrication by human lubricin : effect of disulfide bonds and enzymatic digestion

Zappone, Bruno, Greene, George W., Oroudjev, Emin, Jay, Gregory D. and Israelachvili, Jacob N. 2008, Molecular aspects of boundary lubrication by human lubricin : effect of disulfide bonds and enzymatic digestion, Langmuir, vol. 24, no. 4, pp. 1495-1508.

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Title Molecular aspects of boundary lubrication by human lubricin : effect of disulfide bonds and enzymatic digestion
Author(s) Zappone, Bruno
Greene, George W.ORCID iD for Greene, George W.
Oroudjev, Emin
Jay, Gregory D.
Israelachvili, Jacob N.
Journal name Langmuir
Volume number 24
Issue number 4
Start page 1495
End page 1508
Total pages 14
Publisher American Chemical Society
Place of publication Washington, D. C.
Publication date 2008-02-19
ISSN 0743-7463
Keyword(s) boundary lubrication
enzymatic digestion
human lubricin
Summary Lubricin (LUB) is a glycoprotein of the synovial cavity of human articular joints, where it serves as an antiadhesive, boundary lubricant, and regulating factor for the cartilage surface. It has been proposed that these properties are related to the presence of a long, extended, heavily glycosylated and highly hydrated mucinous domain in the central part of the LUB molecule. In this work, we show that LUB has a contour length of 220 ± 30 nm and a persistence length of ≤10 nm. LUB molecules aggregate in oligomers where the protein extremities are linked by disulfide bonds. We have studied the effect of proteolytic digestion by chymotrypsin and removal of the disulfide bonds, both of which mainly affect the N− and C− terminals of the protein, on the adsorption, normal forces, friction (lubrication) forces, and wear of LUB layers adsorbed on smooth, negatively charged mica surfaces, where the protein naturally forms lubricating polymer brush-like layers. After in situ digestion, the surface coverage was drastically reduced, the normal forces were altered, and both the coefficient of friction and the wear were dramatically increased (the COF increased to μ = 1.1−1.9), indicating that the mucinous domain was removed from the surface. Removal of disulfide bonds did not change the surface coverage or the overall features of the normal forces; however, we find an increase in the friction coefficient from μ = 0.02−0.04 to μ = 0.13−1.17 in the pressure regime below 6 atm, which we attribute to a higher affinity of the protein terminals for the surface. The necessary condition for LUB to be a good lubricant is that the protein be adsorbed to the surface via its terminals, leaving the central mucin domain free to form a low-friction, surface-protecting layer. Our results suggest that this “end-anchoring” has to be strong enough to impart the layer a sufficient resistance to shear, but without excessively restricting the conformational freedom of the adsorbed proteins.
Language eng
Field of Research 030603 Colloid and Surface Chemistry
090301 Biomaterials
Socio Economic Objective 920116 Skeletal System and Disorders (incl. Arthritis)
HERDC Research category C1.1 Refereed article in a scholarly journal
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Document type: Journal Article
Collection: Institute for Frontier Materials
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