Synthesis and biomedical applications of mucin mimic materials

Abstract

Mucin glycoproteins are the major component of mucus and coat epithelial cell surfaces forming the glycocalyx. The glycocalyx and mucus are involved in the transport of nutrients, drugs, gases, and pathogens toward the cell surface. Mucins are also involved in diverse diseases such as cystic fibrosis and cancer. Due to inherent heterogeneity in native mucin structure, many synthetic materials have been designed to probe mucin chemistry, biology, and physics. Such materials include various glycopolymers, low molecular weight glycopeptides, glycopolypeptides, polysaccharides, and polysaccharide-protein conjugates. This review highlights advances in the area of design and synthesis of mucin mimic materials, and their biomedical applications in glycan binding, epithelial models of infection, therapeutic delivery, vaccine formulation, and beyond.

Keywords: Glycopolymer; Glycopolypeptide; Mucin; Mucus.

Fig. 1.

Mucin glycoproteins are found in A) the glycocalyx on the cell surface and B) in secreted mucus; B) Molecular components of mucins including their Pro, Thr, Ser PTS domains, and diverse glycans attached to Ser/Thr including the structures depicted.

Fig. 2.

General procedure for production of peptides by SPPS.

Fig. 3.

SPPS peptides used in Hayakawa et al. studies on the effect of consecutively glycosylated threonines in TTX motifs in mucin TRs [39]. A) Chemical structure of the general TTX 9-mer TR glycopeptides. B) Chemical structures of the 19-mer peptide and glycopeptides containing the 16-mer MUC2 TR with two different TTX motifs. Additional AA’s were added to the 16-mer MUC2 TR sequence to place the TTX motifs in a more central region of the peptide.

Fig. 4.

ROMP glycopolymers generated by Kruger et al. as mucin-mimics to study the influence of cis or trans-polynorbornene backbones on its ability to inhibit Ctx [27]. Glycopolymers were selectively synthesized using two different alkylidene metal catalysts and had DPs of 200 or 500. The Gal substitution [25, 50, 75, or 100%) was added post-polymerization and ethanolamine was used to cap sidechains that did not have a Gal modification.

Fig. 5.

Chemical structures of mucin-mimic glycopolymers formed through RAFT polymerizations.

Fig. 6.

Preparation and polymerization of NCAs to polypeptides and the current scope of glycosylated monomers that have been prepared.

Fig. 7.

Polymerization of Pro NCA to polyPro homo- and co-polypeptides via amidoaminate initiators. Pro is an essential amino acid in mucin PTS domains.

Fig. 8.

Preparation of mucin mimic glycosylated bottlebrush polypeptides by dual catalysis NCA polymerization.

Fig. 9.

Chemical structures of polysaccharides used as mucin mimics; A) agarose, B) cellulose, and C) locust bean gum.

Fig. 10.

Chemical structures of mucin mimetic polymeric scaffolds; A) polyethylene glycol (PEG), B) poly(N-(2-hydroxypropyl) methacrylamide) (pHPMA), and C) polylactic acid (PLA).

Fig. 11.

Seifried et al. method of assembling glycoprotein mimics using global amino acid substitution and biorthogonal ligation. [131].

Fig. 12.

Microarray attachment of glycopeptides. A) Microarray fabrication based on the “glycoblotting method.” B) NHS ester coupling method for microarray attachment.

Fig. 13.

Glycocalyx engineering with lipid-anchored glycopolymers. Glycopolymers end-functionalized with lipids are incubated with cells and passively self-assemble into the plasma membrane.

Fig. 14.

Assembly of protein-anchored mucin chimeras. Membrane proteins were engineered for site-specific display of norbornene amino acids. Tetrazine-functionalized glycopolypeptides were bioorthogonally ligated to the norbornene residues to engineer the glycocalyx of live cells.

Fig. 15.

Native mucoadhesion includes chemical forces, such as hydrogen bonding, electrostatic interactions, hydrophobic interactions, disulfide bridging, as well as physical phenomena such as swelling and spreading and chain interpenetration and entanglement. Mucin mimics are aimed at recapitulating and isolating these interactions.