Some ideas on SARS-CoV-2 and heparan sulfate
March 20, 2022 by ferniglab
After an interplay on Twitter with a colleague who’s related to #LongCovid and #TeamClots, he requested me for some references. I assumed what to ship, after which realised that references plus one thing a bit greater than a Tweet could be helpful, so right here goes.
A short recap
Our first foray into the interactions of SARS-CoV-2 with heparin, and so with mobile heparan sulfate (HS), was printed simply over 2 years in the past in March 2020, written up on a GoogleDoc on the Friday evening and the next Saturday. This was not a blind stab, however primarily based on earlier work by our Italian colleagues which demonstrated an interplay SARS-CoV with heparin and knowledgeable by comparability the receptor binding area (RBD) of the viruses. Within the subsequent months we firmed up the info, put two extra preprints out after which on the finish of the yr the info have been ultimately printed in a peer reviewed journal.
We had thought of that the SARS-CoV-2 spike protein would possibly use a twin receptor system analogous to that of the fibroblast development elements and plenty of different protein ligands that regulate cell perform in growth, homeostasis and illness. This transpires to be the case. Others within the glycosaminoglycan neighborhood have been energetic, exploring structure-function and the way binding to heparan sulfate is a prerequisite for the Spike protein to load onto ACE-2. Thus, on this respect Spike appears like a basic endogenous heparan sulfate-dependent ligand, requiring a ternary complicated of ligand, heparan sulfate co-receptor and transmembrane protein receptor.
Enter stage left neuropilin-1 (NRP-1). In our pleasure we had forgotten about this. The Spike protein binds NRP-1, e.g., right here. It seemingly that that is at the very least one of many mechanisms whereby it accesses the mind
e.g., right here and right here), by means of binding NRP-1 on olfactory neurones or by way of the blood-brain barrier (NRP1 keep in mind can also be vital in controlling angiogenesis). The interplay with NRP-1 is predictable. NRP-1 binds heparin and is a heparin binding binding protein. That’s its acidic domains are fairly heparin mimetic and allow it to bind to some, however not at all all, heparin-binding proteins. To confound issues, NRP-1 is a facultative proteoglycan, so can carry a heparan sulfate (or chondroitin sulfate) chain. It’s value noting the anatomical symmetry of the nervous system and the vasculature extends to the molecular degree, with NRP-1 being a main instance of the latter. What the is glycanation standing of NRP-1 on the olfactory neurons? No person is aware of. An attention-grabbing apart right here is the hyperlink between 3-O sulfation of heparan sulfate and NRP-1.
Frustrations
There are lots of, many unfastened ends
The RBD and the Spike protein are very tough proteins to work with. Whatever the supply of the protein, it loses heparin-binding capability very simply, which correlates with a conformational change within the protein, detectable by round dichroism – and this fairly a very long time earlier than any lower in ACE2 binding could be noticed. There may be additionally one thing uncommon within the interplay of the RBD with heparin in vitro. You want SDS to dissociate the RBD (right here and right here). I’ve seen this some years in the past with thrombospondin (TSH), the place we had to make use of urea to dissociate sure thrombospondin. This was by no means printed, as the info have been consequently quite messy. My clarification was that the binding response was a two step course of
TSH + HS = TSH:HS > TSH*:HS
The place TSH* is a conformation induced by the preliminary reversible binding occasion, which leads to complicated that can’t dissociate. One thing related could also be occurring with Spike, and which might imply that heparanase could play an vital position in mediating the loading of SARS-CoV-2 onto ACE2. A minimum of one heparanase inhibitor is a potent in vitro inhibitor of SARS-CoV-2 an infection and it could be that the inhibitory results of quite a few sulfated sugars are due partially to inhibiting heparanase.
Remedy
First to vent some frustration. The world spent hundreds of thousands on medical trials primarily based on fraudulent knowledge (hydroxychloroquine, ivermectin) whereas individuals have been dying, and nothing on trials targetting the heparan sulfate-dependent mechanism of SARS-CoV-2. This even though (1) coagulopathy is treatable with heparins and (2) there are heparan sulfate impressed merchandise which are wonderful stimulators of wound restore within the context of power irritation, e.g., decrease limb diabetic ulcers from OTR3. A medical trial of heparin in non-SARS-CoV-2 ARDS appeared very promising (sadly behind a paywall). We now have a primary research in SARS-CoV-2 and it’s quite disappointing – no main impact.
Why would possibly that be? The more than likely clarification is that heparin is just not the fitting compound. Although broadly used as an anticoagulant, it’s a very specialised fraction of heparan sulfate, produced by the mast cell. In comparison with heparan sulfate, heparin could be very brief, extremely sulfated and lacks the in depth area construction of heparan sulfate. The for much longer heparan sulfate, with its N-acetyl and transition domains separating the sulfated domains has far larger attain and is ready to bend fairly sharply – that is seen with VEGF, which heparin binds quite poorly, because it has bother participating each binding websites on the VEGF dimer. The flexibility of HS to bridge a number of proteins is probably going vital in its capabilities (keep in mind, in tissues and on cells there’s solely heparan sulfate, no heparin). These capabilities relate to binding over 800 extracellular proteins that regulate cell communication. So quite than heparin, a heparanase resistant mimetic of heparan sulfate just like the OTR3 compounds could be the molecules of alternative. There may be as but solely anecdotal off label case experiences, however these all recommend such compounds could also be very efficient each in opposition to SARS-CoV-2 and in reversing the molecular pathology of LongCovid, which embrace, however is just not restricted to microclots.
