Repulsive Backbone–Backbone Interactions Modulate Access to Specific and Unspecific Binding Sites on Surface-Bound Mucins

Abstract

Mucin glycoproteins are the matrix-forming key components of mucus, the innate protective barrier protecting us from pathogenic attack. However, this barrier is constantly challenged by mucin-degrading enzymes, which tend to target anionic glycan chains such as sulfate groups and sialic acid residues. Here, we demonstrate that the efficiency of both unspecific and specific binding of small molecules to mucins is reduced when sulfate groups are enzymatically removed from mucins; this is unexpected because neither of the specific mucinbinding partners tested here targets these sulfate motifs on the mucin glycoprotein. Based on simulation results obtained from a numerical model of the mucin macromolecule, we propose that anionic motifs along the mucin chain establish intramolecular repulsion forces which maintain an elongated mucin conformation. In the absence of these repulsive forces, the mucin seems to adopt a more compacted structure, in which the accessibility of several binding sites is restricted. Our results contribute to a better understanding on how different glycans contribute to the broad spectrum of functions mucin glycoproteins have.

Modulating the Bioactivity of Mucin Hydrogels with Crosslinking Architecture

“…These results confirm that the details in how complex molecules such as mucins are presented to binders can strongly affect their interactions. This was also recently shown for surface-bound mucins and their binding to dextrans, antibodies, [58] and nanoparticles. [59]…”

Structural Alterations of Mucins Are Associated with Losses in Functionality

“…Previously, we demonstrated that lab-purified MUC5AC contain DNA fragments as impurities, and we speculated that those mucin-bound DNA strands might, in fact, help maintain an extended configuration of the mucin glycoprotein. 20 Since DNA strands are strongly polyanionic at physiological pH levels, we assume that they bind to the terminal mucin domains via unspecific electrostatic forces acting between cationic amino acid residues located in the termini and anionic phosphate groups of the DNA backbone. In contrast, DNA binding to the glycosylated mucin domain is unlikely to happen due to the large number of anionic glycans present in this region.…”

“…Several studies indicated that the O-linked glycan chains help maintain the elongated, bottle brush-like conformation of mucins, and two structural features seem to be of critical importance here: on the one hand, the first monosaccharide unit of the oligosaccharide chains, which is always an N-acetylgalactosamine and connects the glycan chains to the peptide backbone; 19 on the other hand anionic monosaccharides (i.e., sialic acids and sulfated glycans), which convey an overall polyanionic character to the mucin glycoprotein. 20 hydrophobic domains, which are partially folded and carry only a small number of glycan chains, which are attached to the backbone via N-glycosidic bonds. 21 Recent experiments have shown that damages to either of these domains can result in severe losses of mucin functionality.…”

The Antimicrobial Peptide Mastoparan X Protects Against Enterohemorrhagic Escherichia coli O157:H7 Infection, Inhibits Inflammation, and Enhances the Intestinal Epithelial Barrier

“…Mucin is the key matrix-forming component of mucus, which is an innate protective barrier that protects the host from pathogenic attack ( Lutz et al, 2020 ). Analyses of IPEC-J2 cells showed that MPX could improve TJ protein expression after E. coli infection.…”