Multivalent glycocyclopeptides: conjugation methods and biological applications

Spot the difference in reactivity: a comprehensive review of site-selective multicomponent conjugation exploiting multi-azide compounds

Going beyond the conventional approach of pairwise conjugation between two molecules, the integration of multiple components onto a central scaffold molecule is essential for the development of high-performance molecular materials with multifunctionality. This approach also facilitates the creation of functionalized molecular probes applicable in diverse fields ranging from pharmaceuticals to polymeric materials. Among the various click functional groups, the azido group stands out as a representative click functional group due to its steric compactness, high reactivity, handling stability, and easy accessibility in the context of multi-azide scaffolds. However, the azido groups in multi-azide scaffolds have not been well exploited for site-specific use in molecular conjugation. In fact, multi-azide compounds have been well used to conjugate to the same multiple fragments. To circumvent problems of promiscuous and random coupling of multiple different fragments to multiple azido positions, it is imperative to distinguish specific azido positions and use them orthogonally for molecular conjugation. This review outlines methods and strategies to exploit specific azide positions for molecular conjugation in the presence of multiple azido groups. Illustrative examples covering di-, tri- and tetraazide click scaffolds are included.

Morphological Transformation and Surface Engineering of Glycovesicles Driven by Bioinspired Hydrogen Bonds of Nucleobases

Glycopolymer-based supramolecular glycoassemblies with signal-driven cascade morphological deformation and accessible surface engineering toward bioinspired functional glycomaterials have attracted much attention due to their diverse applications in fundamental and practical scenarios. Herein, we achieved the cascade morphological transformation and surface engineering of a nucleobase-containing polymeric glycovesicle through exploiting the bioinspired complementary multiple hydrogen bonds of complementary nucleobases. First, the synthesized thymine-containing glycopolymers (PGal30-b-PTAm249) are capable of self-assembling into well-defined glycovesicles. Several kinds of amphiphilic adenine-containing block copolymers with neutral, positive, and negative charges were synthesized to engineer the glycovesicles through the multiple hydrogen bonds between adenine and thymine. A cascade of morphological transformations from vesicles to ruptured vesicles with tails, to worm-like micelles, and finally to spherical micelles were observed via continuously adding the adenine-containing polymer into the thymine-containing glycovesicles. Furthermore, the surface charge properties of these glyconano-objects can be facilely regulated through incorporating various adenine-containing polymers. This work demonstrates the potential application of a unique bioinspired approach to precisely engineer the morphology and surface properties of glycovesicles for boosting their biological applications.

Comprehensive characterization of polyproline tri-helix macrocyclic nanoscaffolds for predictive ligand positioning

Multivalent ligands hold promise for enhancing avidity and selectivity to simultaneously target multimeric proteins, as well as potentially modulating receptor signaling in pharmaceutical applications. Essential for these manipulations are nanosized scaffolds that precisely control ligand display patterns, which can be achieved by using polyproline oligo-helix macrocyclic nanoscaffolds via selective binding to protein oligomers and cell surface receptors. This work focuses on synthesis and structural characterization of different-sized polyproline tri-helix macrocyclic (PP3M) scaffolds. Through combined analysis of circular dichroism (CD), small- and wide-angle X-ray scattering (SWAXS), electron spin resonance (ESR) spectroscopy, and molecular modeling, a non-coplanar tri-helix loop structure with partially crossover helix ends is elucidated. This structural model aligns well with scanning tunneling microscopy (STM) imaging. The present work enhances the precision of nanoscale organic synthesis, offering prospects for controlled ligand positioning on scaffolds. This advancement paves the way for further applications in nanomedicine through selective protein interaction, manipulation of cell surface receptor functions, and developments of more complex polyproline-based nanostructures.

The functional roles of protein glycosylation in human maternal-fetal crosstalk

BACKGROUND

The establishment of maternal-fetal crosstalk is vital to a successful pregnancy. Glycosylation is a post-translational modification in which glycans (monosaccharide chains) are attached to an organic molecule. Glycans are involved in many physiological and pathological processes. Human endometrial epithelium, endometrial gland secretions, decidual immune cells, and trophoblasts are highly enriched with glycoconjugates and glycan-binding molecules important for a healthy pregnancy. Aberrant glycosylation in the placenta and uterus has been linked to repeated implantation failure and various pregnancy complications, but there is no recent review summarizing the functional roles of glycosylation at the maternal-fetal interface and their associations with pathological processes.

OBJECTIVE AND RATIONALE

This review aims to summarize recent findings on glycosylation, glycosyltransferases, and glycan-binding receptors at the maternal-fetal interface, and their involvement in regulating the biology and pathological conditions associated with endometrial receptivity, placentation and maternal-fetal immunotolerance. Current knowledge limitations and future insights into the study of glycobiology in reproduction are discussed.

SEARCH METHODS

A comprehensive PubMed search was conducted using the following keywords: glycosylation, glycosyltransferases, glycan-binding proteins, endometrium, trophoblasts, maternal-fetal immunotolerance, siglec, selectin, galectin, repeated implantation failure, early pregnancy loss, recurrent pregnancy loss, preeclampsia, and fetal growth restriction. Relevant reports published between 1980 and 2023 and studies related to these reports were retrieved and reviewed. Only publications written in English were included.

OUTCOMES

The application of ultrasensitive mass spectrometry tools and lectin-based glycan profiling has enabled characterization of glycans present at the maternal-fetal interface and in maternal serum. The endometrial luminal epithelium is covered with highly glycosylated mucin that regulates blastocyst adhesion during implantation. In the placenta, fucose and sialic acid residues are abundantly presented on the villous membrane and are essential for proper placentation and establishment of maternal-fetal immunotolerance. Glycan-binding receptors, including selectins, sialic-acid-binding immunoglobulin-like lectins (siglecs) and galectins, also modulate implantation, trophoblast functions and maternal-fetal immunotolerance. Aberrant glycosylation is associated with repeated implantation failure, early pregnancy loss and various pregnancy complications. The current limitation in the field is that most glycobiological research relies on association studies, with few studies revealing the specific functions of glycans. Technological advancements in analytic, synthetic and functional glycobiology have laid the groundwork for further exploration of glycans in reproductive biology under both physiological and pathological conditions.

WIDER IMPLICATIONS

A deep understanding of the functions of glycan structures would provide insights into the molecular mechanisms underlying their involvement in the physiological and pathological regulation of early pregnancy. Glycans may also potentially serve as novel early predictive markers and therapeutic targets for repeated implantation failure, pregnancy loss, and other pregnancy complications.

Convergent synthesis of a hexadecavalent heterobifunctional ABO blood group glycoconjugate

Naturally occurring glycans are often found in a multivalent presentation. Cell surface receptors that recognize these displays may form clusters, which can lead to signalling or endocytosis. One of the challenges in generating synthetic displays of multivalent carbohydrates is providing high valency as well as access to heterofunctional conjugates to allow attachment of multiple antigens or payloads. We designed a strategy based on a set of bifunctional linkers to generate a heterobifunctional multivalent display of two carbohydrate antigens to bind BCR and CD22 with four and twelve antigen copies, respectively. We confirmed that the conjugates were able to engage both CD22 and BCR on cells by observing receptor clustering. The strategy is modular and would allow for alternative carbohydrate antigens to be attached bearing amine and alkyne groups and should be of interest for the development of immunomodulators and vaccines.

Amphiphilic Low-Molecular-Weight Gelators Bearing β-S-N-Acetylglucosamine Linked to a Tartaric Acid Scaffold: Synthesis, Self-Assembly and Wheat Germ Agglutinin Binding

The self-assembly of carbohydrate-based amphiphiles can lead to colloidal soft materials such as supramolecular gels featuring highly desirable characteristics like biodegradability and biocompatibility. The report herein presents the synthesis, characterization and supramolecular self-assembly, physical gelation and wheat lectin binding of two structurally related amphiphilic compounds having β-S-N-acetylglucosamine residues linked to a 2,3-diacyl-N,N'-dipropargylated-l-tartaric diamide. A 1-thio-β-N-acetyl-d-glucosamine precursor attached to a conveniently functionalized linker with an azido group was synthesized by means of a one-pot procedure followed by deprotection. A click reaction successfully led to the two amphiphiles, which differed in length of the fatty acid attached to the tartaric acid scaffold. Although both compounds are poorly soluble in water and organic solvents, the difference in terms of hydrophilic moieties provided them with distinct supramolecular gelation properties. While the presence of an octadecyl chain produced a hydrogelator, the dodecadecyl homologue would only form weak gels in DMSO. SEM and rheology experiments confirmed the characteristic fibrillar morphology and viscoelastic properties, in agreement with the presence of physical gels. Both amphiphiles were able to interact reversibly with wheat germ agglutinin (WGA), a lectin that specifically recognizes GlcNAc residues, indicating a potential use in the food industry, as a gluten sensitivity manager, as well as in health-related industries, for example, for drug delivery systems.

Merging Solid-Phase Peptide Synthesis and Automated Glycan Assembly to Prepare Lipid-Peptide-Glycan Chimeras

Biomaterials with improved biological features can be obtained by conjugating glycans to nanostructured peptides. Creating peptide-glycan chimeras requires superb chemoselectivity. We expedite access to such chimeras by merging peptide and glycan solid-phase syntheses employing a bifunctional monosaccharide. The concept was explored in the context of the on-resin generation of a model α(1→6)tetramannoside linked to peptides, lipids, steroids, and adamantane. Chimeras containing a β(1→6)tetraglucoside and self-assembling peptides such as FF, FFKLVFF, and the amphiphile palmitoyl-VVVAAAKKK were prepared in a fully automated manner. The robust synthetic protocol requires a single purification step to obtain overall yields of about 20 %. The β(1→6)tetraglucoside FFKLVFF chimera produces micelles rather than nanofibers formed by the peptide alone as judged by microscopy and circular dichroism. The peptide amphiphile-glycan chimera forms a disperse fiber network, creating opportunities for new glycan-based nanomaterials.

Multivalent glycosystems for human lectins

Human lectins are involved in a wide variety of biological processes, both physiological and pathological, which have attracted the interest of the scientific community working in the glycoscience field. Multivalent glycosystems have been employed as useful tools to understand carbohydrate-lectin binding processes as well as for biomedical applications. The review shows the different scaffolds designed for a multivalent presentation of sugars and their corresponding binding studies to lectins and in some cases, their biological activities. We summarise this research by organizing based on lectin types to highlight the progression in this active field. The paper provides an overall picture of how these contributions have furnished relevant information on this topic to help in understanding and participate in these carbohydrate-lectin interactions.

Combinational antitumor strategies of exosomes as drug carriers: Mini review

Cancer therapies have made tremendous progress in the last decade, but monotherapy still has apparent limitations and lacks therapeutic efficacy. Thus, the simultaneous administration of multiple drugs has been widely explored and has shown better outcomes. Exosomes, deriving from almost all living cells, are natural nanocarriers designed to deliver drugs to tumor sites. Therefore, combinational antitumor therapies based on exosomes, such as engineered exosomes and different combinations of chemotherapeutic agents, therapeutic nucleic acids, photosensitizers, immunotherapy and phytochemicals, have considerable prospects and potential for clinical translation. Here, we summarize current strategies of cancer combination therapy in exosomes and propose opportunities and challenges in the future.