Heparan Sulfate Proteoglycans as Attachment Factor for SARS-CoV-2

Abstract

Severe acute respiratory syndrome-related coronavirus 2 (SARS-CoV-2) is causing an unprecedented global pandemic demanding the urgent development of therapeutic strategies. Microarray binding experiments, using an extensive heparan sulfate (HS) oligosaccharide library, showed that the receptor binding domain (RBD) of the spike of SARS-CoV-2 can bind HS in a length- and sequence-dependent manner. A hexasaccharide composed of IdoA2S-GlcNS6S repeating units was identified as the minimal binding epitope. Surface plasmon resonance showed the SARS-CoV-2 spike protein binds with a much higher affinity to heparin ( K D = 55 nM) compared to the RBD ( K D = 1 μM) alone. It was also found that heparin does not interfere in angiotensin-converting enzyme 2 (ACE2) binding or proteolytic processing of the spike. However, exogenous administered heparin or a highly sulfated HS oligosaccharide inhibited RBD binding to cells. Furthermore, an enzymatic removal of HS proteoglycan from physiological relevant tissue resulted in a loss of RBD binding. The data support a model in which HS functions as the point of initial attachment allowing the virus to travel through the glycocalyx by low-affinity high-avidity interactions to reach the cell membrane, where it can engage with ACE2 for cell entry. Microarray binding experiments showed that ACE2 and HS can simultaneously engage with the RBD, and it is likely no dissociation between HS and RBD is required for binding to ACE2. The results highlight the potential of using HS oligosaccharides as a starting material for therapeutic agent development.

Endothelial Cell Activation by SARS-CoV-2 Spike S1 Protein: A Crosstalk between Endothelium and Innate Immune Cells

“…Indeed, while clinical evidences and post-mortem studies have provided evidences of SARS-CoV-2 entry into the cells [ 4 , 10 ], only very low levels up to the absence of the ACE2 receptor have been detected in the endothelium [ 11 ]. In this regard, however, several cell-surface receptors other than the ACE2 have been shown to mediate viral entry into the cells [ 12 , 13 ]; moreover, co-receptors such as neuropilin-1 (NRP1) and neuropilin-2 (NRP-2) are of a certain relevance in the infectivity of Sars-Cov-2 [ 14 ]. Neuropilin-1, in particular, is essential for vascular development and the maintenance of endothelial homeostatic function, and promotes physiological and pathological angiogenesis [ 15 ]; furthermore, it has been shown to regulate the endothelium-dependent inflammatory responses at the level of the blood–brain barrier [ 16 ].…”

On the Selectivity of Heparan Sulfate Recognition by SARS-CoV-2 Spike Glycoprotein

“…In contrast, Boons and co-workers report that the IdoA2S–GlcNS6S is the preferred binding partner of RBD with not much role for the lone 3S group of GlcNS6S in their HS library. 31 …”

“… 30 These successes have led the two groups to study an impressive array of 80 HS oligosaccharides of varying lengths and sulfation patterns for binding to SgP proteins. 31 They identified a fairly select group of sequences that bind to SgP proteins with affinities in the nanomolar to micromolar range. A major conclusion of these studies was that the common heparin (Hp) sequence, referred to as IdoA2S–GlcNS6S, was preferentially recognized by SgP proteins, e.g., the SgP trimer or the RBD.…”

COVID-19 and Diabetes: A Comprehensive Review of Angiotensin Converting Enzyme 2, Mutual Effects and Pharmacotherapy

“…COVID-19 patients usually present with thrombosis complications, including microthrombosis, venous thromboembolism and stroke, and often receive therapeutic unfractionated heparin (UFH) or low molecular weight heparin. Both drugs can block viral infection (244,245). Plasma heparin levels of 0.3 -0.7 unit/mL (equivalent to 1.6-4 mg/mL) can achieve effective anticoagulation, and this concentration is sufficient to prevent the S protein from binding cells.…”