Thermostability of bovine submaxillary mucin (BSM) in bulk solution and at a sliding interface

Thermostability of bovine submaxillary mucin (BSM) was studied in terms of its structure, hydrodynamic size, surface adsorption, and lubricating properties in the temperature range of 5-85°C. The overall random coil structure of BSM showed a gradual loosening with increasing temperature as characterized by circular dichroism (CD) spectroscopy, but this change was fully reversible upon lowering temperature. Extended heating up to 120 min at 80°C did not make any appreciable changes in the structure of BSM when it was cooled to room temperature. The hydrodynamic size of BSM, as studied by dynamic light scattering (DLS), showed a slight increase after heating at high temperature (80°C). Optical waveguide lightmode spectroscopy (OWLS) studies showed facile adsorption of BSM onto poly(dimethylsiloxane) (PDMS) surface (>180 ng/cm(2)) at room temperature due to its amphiphilic characteristics. Adsorbed mass of BSM was noticeably reduced after heating at 80°C, possibly resulting from its aggregation. BSM showed excellent lubricity at self-mated sliding contacts between PDMS at room temperature or lower (friction coefficient≈0.02), even when BSM solution was pre-heated up to 120 min at 80°C. Gradual degradation of lubricity of BSM was observed with increasing temperature, but it was also reversibly recovered with decreasing temperature. Structural and functional stability of BSM against heating is proposed to originate from heavy glycosylation and lack of higher degree of protein structure in BSM.