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 believed what to ship, after which realised that references plus one thing a bit greater than a Tweet may 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 revealed 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 based mostly 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 had been finally revealed 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 progress components and plenty of different protein ligands that regulate cell perform in improvement, homeostasis and illness. This transpires to be the case. Others within the glycosaminoglycan group had been lively, 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 seems like a traditional endogenous heparan sulfate-dependent ligand, requiring a ternary advanced 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 probably that that is at the very least one of many mechanisms whereby it accesses the mind
e.g., right here and right here), by binding NRP-1 on olfactory neurones or by way of the blood-brain barrier (NRP1 bear in mind can be necessary 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 moderately heparin mimetic and allow it to bind to some, however in no way 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 price noting the anatomical symmetry of the nervous system and the vasculature extends to the molecular stage, with NRP-1 being a chief instance of the latter. What the is glycanation standing of NRP-1 on the olfactory neurons? No person is aware of. An fascinating apart right here is the hyperlink between 3-O sulfation of heparan sulfate and NRP-1.
Frustrations
There are lots of, many free ends
The RBD and the Spike protein are very tough proteins to work with. Whatever the supply of the protein, it loses heparin-binding capacity 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 will 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 revealed, as the info had been consequently fairly messy. My rationalization 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 advanced that can’t dissociate. One thing comparable could also be taking place with Spike, and which might imply that heparanase might play an necessary position in mediating the loading of SARS-CoV-2 onto ACE2. Not less than one heparanase inhibitor is a potent in vitro inhibitor of SARS-CoV-2 an infection and it could be that the inhibitory results of numerous sulfated sugars are due partially to inhibiting heparanase.
Remedy
First to vent some frustration. The world spent hundreds of thousands on scientific trials based mostly on fraudulent information (hydroxychloroquine, ivermectin) whereas folks had been dying, and nothing on trials targetting the heparan sulfate-dependent mechanism of SARS-CoV-2. This although (1) coagulopathy is treatable with heparins and (2) there are heparan sulfate impressed merchandise which are glorious stimulators of wound restore within the context of power irritation, e.g., decrease limb diabetic ulcers from OTR3. A scientific trial of heparin in non-SARS-CoV-2 ARDS appeared very promising (sadly behind a paywall). We now have a primary examine in SARS-CoV-2 and it’s fairly disappointing – no main impact.
Why would possibly that be? The more than likely rationalization is that heparin is just not the correct compound. Although extensively used as an anticoagulant, it’s a very specialised fraction of heparan sulfate, produced by the mast cell. In comparison with heparan sulfate, heparin may be very quick, 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 higher attain and is ready to bend fairly sharply – that is seen with VEGF, which heparin binds fairly 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 necessary in its capabilities (bear in mind, in tissues and on cells there may be solely heparan sulfate, no heparin). These capabilities relate to binding over 800 extracellular proteins that regulate cell communication. So fairly than heparin, a heparanase resistant mimetic of heparan sulfate just like the OTR3 compounds often is the molecules of alternative. There may be as but solely anecdotal off label case reviews, however these all counsel such compounds could also be very efficient each towards SARS-CoV-2 and in reversing the molecular pathology of LongCovid, which embrace, however is just not restricted to microclots.