Many pathogens take advantage of the dependence of the host on the interaction of hundreds of extracellular proteins with the glycosaminoglycans heparan sulphate to regulate homeostasis and use heparan sulphate as a means to adhere and gain access to cells. Moreover, mucosal epithelia such as that of the respiratory tract are protected by a layer of mucin polysaccharides, which are usually sulphated. Consequently, the polydisperse, natural products of heparan sulphate and the allied polysaccharide, heparin have been found to be involved and prevent infection by a range of viruses including S-associated coronavirus strain HSR1. Here we use surface plasmon resonance and circular dichroism to measure the interaction between the SARS-CoV-2 Spike S1 protein receptor binding domain (SARS-CoV-2 S1 RBD) and heparin. The data demonstrate an interaction between the recombinant surface receptor binding domain and the polysaccharide. This has implications for the rapid development of a first-line therapeutic by repurposing heparin and for next-generation, tailor-made, GAG-based antivirals.

Single-chain simulations of densely branched comb polymers, or “molecular bottle-brushes” with side-chains attached to every (or every second) backbone monomer, were carried out by off-lattice Monte Carlo technique. A coarse-grained model, described by hard spheres connected by harmonic springs, was employed. Backbone lengths of up to 100 units were considered, and compared with the corresponding linear chains. The backbone molecular size was investigated as a function of its length at fixed arm size, and as a function of the arm size at fixed backbone length. The apparent swelling exponents obtained by a power-law fit were found to be larger than those for the corresponding linear polymers, indicative of stiffening of the comb backbone. The probability distribution function for the backbone end-to-end distance was also investigated for different backbone lengths and arm sizes. Analysis of this function yielded the critical exponents, which revealed an increase in the swelling exponent consistent with values found from the molecular size. The apparent persistence length of the backbone was also determined, and was found to increase with increasing branching density. Finally, the static structure factors of the whole bottle-brushes and of their backbones are discussed, which provides another consistent estimate of the swelling exponents.

The 3-O-sulfation of N-sulfated glucosamine is the last event in the biosynthesis of heparin/heparan sulfate, giving rise to the antithrombin-binding pentasaccharide sequence AGA*IA, which is largely associated with the antithrombotic activity of these molecules. The aim of the present study was the structural and biochemical characterization of a previously unreported AGA*IA*-containing octasaccharide isolated from the very-low-molecular-mass heparin semuloparin, in which both glucosamine residues of the pentasaccharide moiety located at the non-reducing end bear 3-O-sulfate groups. Two-dimensional and STD (saturation transfer difference) NMR experiments clearly confirmed its structure and identified its ligand epitope binding to antithrombin. The molecular conformation of the octasaccharide–antithrombin complex has been determined by NMR experiments and docking/energy minimization. The presence of the second 3-O-sulfated glucosamine in the octasaccharide induced more than one order of magnitude increase in affinity to antithrombin compared to the pentasaccharide AGA*IA.