Daoyu Profile picture
31 May, 6 tweets, 2 min read
This is not correct. Cell penetrating peptides AKA peptides with a lot of positive charges, are extremely hard to secrete because they will stick to the membranes and go back into the cells pubmed.ncbi.nlm.nih.gov/24928321/ even if it was prevented from being cleaved by furin.
This is in fact one of the reasons why the SARS-CoV-2 virion carry much less Spike than SARS-CoV per virion, especially if a pseudotype system is used and the S was D614.
Consecutive positive charges in cells are associated with NLS sequences of intracellular proteins. Not exactly what you see on Spike proteins. Some of these basic sites are associated with VERO E6 passage and is deleted in live hosts.
Highly basic peptides are also susceptible to proteolysis which result in their poor stability. Again seen in WuHu-1 where up to 2/3 of the S1 is shed. ncbi.nlm.nih.gov/pmc/articles/P…
The combined effect is the very high susceptibility of the S toward denaturation by antibody binding. nature.com/articles/s4146…

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More from @Daoyu15

31 May
The DRNTRD(E) sequences found in SARS-CoV and many bat-CoVs are in fact, NOT furin sites. this is because the sequence is located in a highly conserved position that is on the inside of the S2 subunit, shielded behind the S1 from
the other protomer. This site is not only completely furin resistant (both end was topologically anchored behind the other S1 and therefore remain bound to S2 and inaccessible to furin binding) but is in fact, located inside a trypsin-resistant zone of the S protein.
the PDB entry rcsb.org/3d-view/6ACD is the SARS-CoV S treated with low temperature and Trypsin. despite having both S1-S2 and S2' cleaved by trypsin, the RNTR sequence remained intact and uncleaved.
rcsb.org/3d-view/7CN8 is a homologous S with the sequence KNTQ from GX-S.
Read 16 tweets
30 May

Viral recombination does not respect the reading frames of the target RNA. The nucleotide sequence is not present in any other RNA that the virus could encounter. It is absent in mammals or viruses, particularly the genomes and transcriptomes of bat,
This mean that there exist no source of the insert anywhere in plausible hosts and plausible intermediate hosts for SARS-CoV-2, and the only RNA that it could encounter for sufficient terminal homology that allow it’s insertion by recombination in a mammalian cell will be the
Read 4 tweets
20 May
@Gurdur The issue with canine Coronavirus and feline Coronavirus is the fact that these Alpha-CoVs are 1: found in companion animals. It circulate in all dogs and cats near human. 2: are the principal component of FIPV. It does not have an obscure origin (only found in Mojiang
@Gurdur ,1000Km+ from Wuhan) and It does not have an improbable location for “spillover” (it is found directly in dogs and cats all throughout the world, no “wildlife” is needed.).
@Gurdur This does not have any of the unusual properties of SARS-CoV-2, and it is well rooted in circulating CCoVs and FCoVs. It is extremely unlikely that this is pathogenic in humans, and may represent occasional epizootic escape of companion animal CoVs (alongside with PDCoV)
Read 16 tweets
18 May
How did an unprotected RNA molecule get to the outside of a membrane? how does a cell secrete RNA? is it endolysosomal retrograde transport or is it an actual secretory pathway? RNA constructs does not elict specific immunity so this is a way to engineer
novel functions (like virus neutralization, protein binding, catalytic activity(ribozymes)) without the immunogenicity backside.
Ribozymes are generally regarded as non-immunogenic, so does aptamers. this just opened up a lot of engineering options for in-vivo applications. for RNA catalytic activity and/or binding activiy, use the SELEX protocol. (TMA-Assay-Selection-TMA)
Read 4 tweets
17 May
@wanderer_jasnah Not only does the nucleotides wrong (it was CCACGGCGAGCA), but it is very possible that in a cell culture that is not VERO E6, the Pro emerges as a compromise to create an uncleaved (due to the O-linked glycans absent in human cells, but present in insect cells) RRAR
@wanderer_jasnah jvi.asm.org/content/82/12/… that is precisely what that is needed for a Cell culture adapted Coronavirus. biorxiv.org/content/10.110… caLu-3. The model for human lungs in the WIV. The one model that is relevant and used again and again. jvi.asm.org/content/jvi/ea…
@wanderer_jasnah The CCTCGGCGGGCA is only one nucleotide different from CGTCGGCGGGCA which encodes RRRAR. google.com/amp/s/www.rese… this is used in a FCS before.
Read 30 tweets

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