Oligoguluronate induced competitive displacement of mucin–alginate interactions: relevance for mucolytic function

Abstract

The rheological properties of mucin–alginate blends can be modulated by addition of oligoguluronates. In the present study, we report on destabilisation of mucin–alginate interactions by oligoguluronates as determined by forced unbinding of these macromolecular components. The forces needed to rupture the bonds formed between purified pig gastric mucin (PGM) and high molecular weight alginate, covalently linked to mica and the AFM tip, respectively were determined under physiologically relevant conditions. The experiments were conducted in the presence and absence of oligoguluronate with DP_n = 12 in concentrations ranging from 0.001 to 2 mg ml⁻¹ in buffer solution. The PGM–alginate forced unbinding profiles revealed unbinding events with magnitudes up to 4 nN occurring at separation distances up to 3 μm. The observed unbinding profiles were consistent with a multivalent nature of the macromolecular compounds. The oligoguluronate concentration-dependent suppression of mucin–alginate interactions modelled as a one-site competitive model yielded an estimate of 1.4 μg ml⁻¹ oligoguluronate for 50% reduction of the mucin–alginate deadhesion work. Analysis of interaction patterns between alginate and mucin immobilized on the AFM tip probed independently against immobilised oligoguluronate suggests that oligoguluronate interaction with mucin is the mechanism underlying the observed suppression of the alginate–mucin interactions. The oligoguluronate concentration-dependent suppression of mucin–alginate interactions increases the molecular understanding of oligoguluronates' action as an apparent mucolytic agent of potential relevance for application to improve lung function in patients suffering from cystic fibrosis.