Chemically modified tandem repeats in proteins: natural combinatorial peptide libraries

Implications of Mucin-Type O-Glycosylation in Alzheimer's Disease

Alzheimer's disease (AD) is one of the most common neurodegenerative disorders linked to aging. Major hallmarks of AD pathogenesis include amyloid-β peptide (Aβ) plaques, which are extracellular deposits originating from the processing of the amyloid precursor protein (APP), and neurofibrillary tangles (NFTs), which are intracellular aggregates of tau protein. Recent evidence indicates that disruptions in metal homeostasis and impaired immune recognition of these aggregates trigger neuroinflammation, ultimately driving disease progression. Therefore, a more comprehensive approach is needed to understand the underlying causes of the disease. Patients with AD present abnormal glycan profiles, and most known AD-related molecules are either modified with glycans or involved in glycan regulation. A deeper understanding of how O-glycosylation influences the balance between amyloid-beta peptide production and clearance, as well as microglia's pro- and anti-inflammatory responses, is crucial for deciphering the early pathogenic events of AD. This review aims to provide a comprehensive summary of the extensive research conducted on the role of mucin-type O-glycosylation in the pathogenesis of AD, discussing its role in disease onset and immune recognition.

Positional Scanning MUC1 Glycopeptide Library Reveals the Importance of PDTR Epitope Glycosylation for Lectin Binding

One of the main barriers to explaining the functional significance of glycan-based changes in cancer is the natural epitope heterogeneity found on the surface of cancer cells. To help address this knowledge gap, we focused on designing synthetic tools to explore the role of tumor-associated glycans of MUC1 in the formation of metastasis via association with lectins. In this study, we have synthesized for the first time a MUC1-derived positional scanning synthetic glycopeptide combinatorial library (PS-SGCL) that vary in number and location of cancer-associated Tn antigen using the "tea bag" approach. The determination of the isokinetic ratios necessary for the equimolar incorporation of (glyco)amino acids mixtures to resin-bound amino acid was determined, along with developing an efficient protocol for on resin deprotection of O-acetyl groups. Enzyme-linked lectin assay was used to screen PS-SGCL against two plant lectins, Glycine max soybean agglutinin and Vicia villosa. The results revealed a carbohydrate density-dependent affinity trend and site-specific glycosylation requirements for high affinity binding to these lectins. Hence, PS-SGCLs provide a platform to systematically elucidate MUC1-lectin binding specificities, which in the long term may provide a rational design for novel inhibitors of MUC1-lectin interactions involved in tumor spread and glycopeptide-based cancer vaccines.

Potentides: New Cysteine-Rich Peptides with Unusual Disulfide Connectivity from Potentilla anserina

Cysteine-rich peptides (CRPs), which are disulfide-constrained peptides with 3 to 5 disulfide bonds and molecular weights of 2 to 6 kDa, are generally hyperstable and resistant to thermal, chemical, and enzymatic degradation. Herein, the discovery and characterization of a novel suite of CRPs, collectively named potentides pA1-pA16 from the root of the medicinal herb Potentilla anserina L, are described. Through a combination of proteomic and transcriptomic methods, it is shown that 35-residue potentide pA3, which is the most abundant member of potentides, exhibits high stability against heat, acidic, and proteolytic degradation. Transcriptomic analysis revealed that potentide precursor sequences contained four tandem repeats in the mature domain, which is the first report on tandem repeats being found in the Rosaceae family. Disulfide mapping showed that potentide pA3 displayed a novel disulfide connectivity of C1-C3, C2-C6, and C4-C5; a cystine motif that has not been reported in plant CRPs. Transcriptomic data mining and a neighbor-joining clustering analysis revealed 56 potentide homologues and their distribution in the families of Rosaceae and Ranunculaceae in angiosperm. Altogether, these results reveal a new plant CRP structure with an unusual cystine connectivity. Additionally, this study expands the families and structure diversity of CRPs as potentially active peptide pharmaceuticals.

Combinatorial biosynthesis of RiPPs: docking with marine life

Ribosomally synthesized natural products are found in all forms of life. Their biosynthesis uses simple ribosomally synthesized peptides as starting materials that are transformed into complex structures via posttranslational modifications, enriched with elaborate chemical scaffolds that make them desirable as pharmacological tools. In addition, these natural products often exhibit combinatorial biosynthesis, making them attractive targets for engineering. An increasing knowledge of their biosynthetic machinery has provided key insights into their fascinating chemistry. Marine organisms have been a rich source of this class of natural products and here we review the lessons learned from marine life that enables exploitation of their potential for combinatorial engineering, opening up new routes for peptide-based drug discovery.