Research

Through photosynthesis, marine algae convert gigatonnes of carbon dioxide into carbohydrates every year. In the form of algal polysaccharides, these structurally complex biomolecules determine to a large extent how much carbon is stored in the oceans. Specialised marine bacteria unlock this carbon energy by breaking down the polysaccharides through the action of carbohydrate-active enzymes (CAZymes) and releasing the carbon dioxide back into the atmosphere. However, some of the polysaccharides are not recycled quickly, but sink into the deep sea and sediments, where they can store carbon for millennia. To better understand these processes, great efforts are needed to further explore the marine carbon cycle. The same advances are also important to support emerging efforts to use algal biomass as a new sustainable resource for the bioeconomy. The enzymatic machinery responsible for the degradation of polysaccharides by marine bacteria has remained largely unexplored because of the size and heterogeneity of algal polysaccharides. Pure and defined oligosaccharides needed for systematic screenings of marine CAZymes are currently not available. Since conventional chemical synthesis is time-consuming and often not general enough, ASAP aims to obtain collections of oligosaccharides related to different classes of algal polysaccharides by using automated glycan assembly (AGA) technology. Oligosaccharides with many different sequences and sulfation patterns will be prepared from small sets of monosaccharide building blocks. Incubation of the synthetic oligosaccharides with samples containing carbohydrate-degrading activity and subsequent HPLC-MS analysis of the degradation products will provide information on: 1) the collective enzyme activities of a bacterial community in seawater and sediment samples; 2) the abilities of individual bacterial strains to degrade specific polysaccharides; 3) the substrate specificities of purified CAZymes.

The HIV-1 envelope spike (Env) bears a cluster of oligomannose-type glycans that is a target for broadly neutralizing antibodies (bnAbs). However, while nAbs to this cluster, dubbed the high-mannose patch (HMP), are known to develop in at least some HIV-infected individuals, past attempts to elicit similar antibodies by immunization have been largely unsuccessful. Most previous approaches have involved presenting clusters of natural or synthetic high-mannose glycans on the surface of carrier proteins. The difficulty in eliciting high-mannose-targeting nAbs by immunization is believed to relate, at least in part, to the ‘self’ nature of the targeted glycans. The approach that we are pursuing is based on the scientific premise that antigenic mimicry of mammalian host structures can stimulate cross-reactive antibodies if such mimics are presented in the proper ‘foreign’ milieu. Our overarching hypothesis is that, upon immunization, an antigenic mimic of mammalian oligomannose will more readily elicit antibodies that bind the HMP than native or synthetic oligomannose. In our progress report, we show that a CRM197-conjugate of our lead oligomannose mimetic is bound with high avidity by various HMP-specific bnAbs as well as their germline precursors. Furthermore, human antibody transgenic mice immunized with this neoglycoconjugate yield antibodies that bind recombinant HIV-1 SOSIP trimers, albeit only when the conjugate is formulated in the TLR4-stimulating Th1-adjuvant GLA-SE. We expect our findings to help sharpen our strategy and critically inform the pursuit of future preclinical studies. Results from this research could inform other HIV vaccine design strategies also.

C-type lectin-like receptor 2 (CLEC-2) is involved in two important processes of platelet biology: separation of blood and lymphatic vessels and thrombosis. Besides being considered a potential drug target in settings of wound healing, inflammation, infection, and cancer, CLEC-2 is gaining interest as a therapeutic target for a variety of thrombo-inflammatory disorders with treatment also predicted to cause minimal disruption to hemostasis. While the last few years have seen major advances in our understanding of CLEC-2 ligand interactions and the resulting signaling cascades, the mechanisms by which the different biological functions are controlled are still insufficiently understood. Elucidation of these pathways is bottlenecked by a lack of chemical tools to investigate and visualize the effects of receptor multimerization on signaling and ligand fate. This project aims at establishing a platelet-specific liposomal platform for mechanistic and targeted-delivery studies. Liposomal nanoparticles are decorated with natural as well as newly developed high-affinity ligands of CLEC-2 prepared by chemical synthesis. The opportunity to control ligand affinity and density on the nanoparticles will enable detailed studies into CLEC-2 biology and thus exploration of CLEC-2 as a therapeutic target for small-molecule inhibitors and for delivery devices for nucleic acids and other drugs.