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Chemical or enzymic reduction/oxidation of integrin cysteine residues (e.g. by reducing agents and protein disulphide isomerase) may be a mechanism for regulating integrin function. It has also been proposed that unique cysteine residues in the integrin 3 subunit are involved in the regulation of alphaIIbeta3. In the present study, we studied systematically the role of disulphide bonds in 3 on the ligand-binding function of alphaIIbbeta3 by mutating individual cysteine residues of beta3 to serine. We found that the disulphide bonds that are critical for alphaIIbbeta3 regulation are clustered within the EGF (epidermal growth factor) domains. Interestingly, disrupting only a single disulphide bond in the EGF domains was enough to activate alphaIIbeta3 fully. In contrast, only two (of 13) disulphide bonds tested outside the EGF domains activated aIIbbeta3. These results suggest that the disulphide bonds in the EGF domains should be intact to keep alphaIIbbeta3 in an inactive state, and that there is no unique cysteine residue in the EGF domain critical for regulating the receptor. The cysteine residues in the EGF domains are potential targets for chemical or enzymic reduction.

The presence of sodium-rich layers on iron oxide surfaces plays an important role in the functionality of glassy lubricants used in harsh working conditions of metal formation. However, the underlying low-friction mechanism of the sodium layer on iron oxide surfaces at the atomic level is not well understood. In this work, Na adsorption on the most stable surface of Fe2O3 (0001) is studied by density functional theory. The most stable adsorption configuration and the modifications induced by the adsorption on the structural as well as the electronic properties of the surface are discussed. By constructing the potential energy surface, we can quantitatively compare the sliding behaviors of two sodium passivated oxide layers with that of clean surfaces. The determination of energy corrugations, sliding paths, static lateral forces, and shear strengths has suggested a significantly lower friction in the Na-passivated system compared to that of the clean surface. The effects of a load on the friction are also investigated. The results indicate that sodium passivation in glass lubricants can help to prevent the direct contact of two oxide surfaces and thereby maintain a low friction and hence wear reduction at high pressures. [ABSTRACT FROM AUTHOR]

A comparative analysis of thin film lubrication of hexadecane between different iron and its oxide surfaces has been carried out using classical molecular dynamic simulation. An ab initio force-field, COMPASS, was applied for n-hexadecane using explicit atom model. An effective potential derived from density functional theory calculation was utilized for the interfacial interaction between hexadecane and the tribo-surfaces. A quantitative surface parameterization was introduced to investigate the influence of surface properties on the structure, rheological properties, and tribological performance of the lubricant. The results show that although the wall-fluid attraction of hexadecane on pure iron surfaces is significantly stronger than its oxides, there is a considerable reduction of shear stress of confined n-hexadecane film between Fe(100) and Fe(110) surfaces compared with FeO(110), FeO(111), Fe2O3(001), and Fe2O3(012). It was found that, in thin film lubrication of hexadecane between smooth iron and iron oxide surfaces, the surface corrugation plays a role more important than the wall-fluid adhesion strength. [ABSTRACT FROM AUTHOR]