Solid-phase synthesis of human salivary mucin-derived O-linked glycopeptides

Abstract

Short glycopeptides derived from salivary mucin have been synthesized in order to delineate the O-glycosylation pattern that is important in the biological activity of mucin. Two glycopeptides, APPETT*AAP-OMe and PAPPSS*SAP-OMe (* = e~-D-GalNAc), were prepared by solid-phase peptide synthesis integrating the Fmoc and Boc strategies. Since these peptides contain a C-terminal proline, we devised an efficient strategy using facile Boc chemistry, where the glycosylation at the desired position in the sequence was achieved using corresponding Frnoc-glycoamino acid esters A and B as building blocks. The transformation of the 2-azido group into the acetamido derivative was performed with thioacetic acid on the polymer-bound glycopeptides. Corresponding nonglycosylated peptides were also synthesized to study the influence of ~-D-GalNAc on peptide backbone conformation.

NMR analysis of human salivary mucin (MUC7) derived O‐linked model glycopeptides: comparison of structural features and carbohydrate–peptide interactions

“…butyl (tBu) chemistry. The O ‐linked glycopeptide constructs used in this study were made using our acetyl‐protected glycan approach followed by convergent coupling to apopeptide and global deprotection (22, 23). All synthetic (glyco)peptides were purified by reversed‐phase high performance liquid chromatography (RP‐HPLC) and their integrity was confirmed by 1 H NMR, amino acid and mass spectral analysis as described earlier (22, 23).…”

“…In an effort to understand the SAR of this highly glycosylated tandem repeat domain of MUC7, we have synthesized chemically several peptides O‐ glycosylated with α‐N‐acetyl galactosamine [GalNAc] and β‐galactopyranosyl (1–3)α‐N‐acetyl galactosamine [Galβ(1–3)GalNAc] at one, two or three sites (22, 23). Since these glycopeptides are derived from the tandem repeat sequence of mucin (MUC7), which are rich in serine/threonine and proline, they could serve as very good models for understanding SAR of mucins in general and of MUC7 in particular.…”

HPLC–MS characterization of cyclo‐statherin Q‐37, a specific cyclization product of human salivary statherin generated by transglutaminase 2

“…This acidic peptide secreted by different salivary glands has an anomalously high content of tyrosine, proline, and glutamine, and a high degree of structural and charge asymmetry [2]. An important role of statherin is connected with its great affinity for calcium phosphate minerals, such as hydroxyapatite (HAP) [3], and with its ability to inhibit precipitation and crystal growth from supersaturated solutions of calcium phosphate [4]. It has also been suggested that statherin may participate in the exchange and transport of calcium and phosphate during the molecular events connected with its secretion in the salivary glands [2], contributing to the distribution of the two ions at the level of the mucosal surface.…”

A peptide that inhibits hydroxyapatite growth is in an extended conformation on the crystal surface

“…The statherin primary amino acid sequence is characterized by a negatively charged N terminus consisting of a DSSEEK sequence, and the serines are post-translationally phosphorylated (19). There is no direct three-dimensional structure information available for statherin, but secondary structure predictions suggest that the N terminus has a propensity for ␣-helix formation, and circular dichroism studies demonstrate the presence of some ␣-helical conformation in solution (20,21). The existence of secondary structure in other acidic proteins has also been predicted and hypothesized to play a role in crystal recognition through lattice-matching mechanisms (22)(23)(24).…”