Small-angle light and X-ray scattering measurements of a protein–oligosaccharide complex mucin in solution

Abstract

The molecular assembly and the chain conformation of intact bovine submaxillary mucin (BSM) in solution over wide-ranging concentrations were characterized by using low-angle laser light scattering and small-angle X-ray scattering (SAXS) methods. The specific refractive index increment of BSM was estimated to be 0.152 ml g−1 and was used to determine the molecular weight of BSM by low-angle laser light scattering photometry combined with high-performance gel chromatography. The total molecular weight of BSM was 55 million and the molecular weight of the main fractionated components was about 2 million. Fractal analysis of the SAXS data revealed that the intact BSM molecule is a chain with excluded volume (fractal dimension 1.67) at concentrations of 1.4 and 3.6 mg ml−1 and a chain with a Gaussian chain character (fractal dimension 2) at concentrations of 7.2–15 mg ml−1. Moreover, the Kratky plots of the SAXS data showed that the chain conformation of BSM molecules is a Gaussian (unfolded) structure in solution. The estimated cross-sectional radius of gyration value lay in the range 0.65–0.76 nm, which is reasonable for a long thin shape.