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 quick 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 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 had been ultimately revealed in a peer reviewed journal.
We had thought-about that the SARS-CoV-2 spike protein may use a twin receptor system analogous to that of the fibroblast progress elements and lots of different protein ligands that regulate cell operate in improvement, homeostasis and illness. This transpires to be the case. Others within the glycosaminoglycan neighborhood had 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 seems like a traditional 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 probably that that is at the least one of many mechanisms whereby it accesses the mind
e.g., right here and right here), via binding NRP-1 on olfactory neurones or through the blood-brain barrier (NRP1 keep in mind can 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 under no circumstances 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 chief instance of the latter. What the is glycanation standing of NRP-1 on the olfactory neurons? No one 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 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 skill 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’s 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 reasonably 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 ends up in complicated that can’t dissociate. One thing comparable could also be taking place with Spike, and which might imply that heparanase might 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 had been dying, and nothing on trials targetting the heparan sulfate-dependent mechanism of SARS-CoV-2. This even supposing (1) coagulopathy is treatable with heparins and (2) there are heparan sulfate impressed merchandise which might be wonderful stimulators of wound restore within the context of continual irritation, e.g., decrease limb diabetic ulcers from OTR3. A medical trial of heparin in non-SARS-CoV-2 ARDS seemed very promising (sadly behind a paywall). We now have a primary research in SARS-CoV-2 and it’s reasonably disappointing – no main impact.
Why may that be? The almost certainly clarification is that heparin isn’t the best 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 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 better attain and is ready to bend fairly sharply – that is seen with VEGF, which heparin binds reasonably 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 may be solely heparan sulfate, no heparin). These capabilities relate to binding over 800 extracellular proteins that regulate cell communication. So reasonably than heparin, a heparanase resistant mimetic of heparan sulfate just like the OTR3 compounds stands out as the molecules of selection. There’s as but solely anecdotal off label case studies, 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 isn’t restricted to microclots.
