Ryan Hisner Profile picture
Jun 6, 2023 18 tweets 6 min read Read on X
What's going on with ORF7b? Something unusual has occurred in ORF7b in two unrelated variants—two of the only non-XBB variants that remain competitive. They took entirely different routes to reach the same end point: a new ORF7b protein.
But first a short primer on ORF7b. 1/
SARS-CoV-2 genes are often divided into three categories:
1. Non-structural proteins (NSPs)
2. Structural proteins (spike, envelope, membrane, nucleocapsid or S, E, M, N)
3. Accessory proteins 2/ Image
The 16 NSPs are in ORF1ab & make up the first ~2/3 of the genome. They have diverse functions, but most are primarily involved in viral replication in one way or another. Here are descriptions of the functions of the 16 NSPs from a few different sources. 3/ ImageImage
Structural proteins (envelope, membrane, spike, nucleocapsid—E, M, S, N) compose the physical structure of the virus. N has also been implicated in innate immune evasion.
4/ Image
Accessory proteins (ORF3a, ORF6, ORF7a, ORF7b, ORF8, ORF9b, & possibly others) are less essential than the first two categories, & seem to be mainly involved in immune evasion. 5/ Image
But it's not always clear what accessory proteins do. ORF8, after having had dozens of powerful functions attributed to it, has been nearly erased, resulting in an apparent increase in fitness. ORF7a has also been destroyed repeatedly. 6/
ORF7b is the smallest protein, at 43 amino acids (AA), & early ORF7b stop codons, which prematurely halt protein construction, have made regular appearances (though not as commonly as in ORF8). At first, the new ORF7b mutations seem similarly destructive of ORF7b. 7/ Image
Each AA is coded by a "codon" made up of 3 nucleotides (nt), so any deletion not divisible by 3 completely changes the composition of the AA appearing after it. This is called a frameshift. Example: a 1-nt deletion in ORF6 in XBB.1.28.1 (spotted by @shay_fleishon). 8/ Image
Frameshifts usually quickly lead to a stop codon, truncating the protein & making it incapable of carrying out its previous function. The 1-nt deletion in ORF6 in XBB.1.28.1, for example, finds a stop codon at AA site #11, hacking off the last 84% of ORF6. 9/ Image
One variant—XBC.1.6, a Deltacron—has a 2-nucleotide deletion in ORF7b codon 13, causing a frameshift. But this frameshift doesn't lead to a stop codon until codon 32-33. 10/ Image
The other variant—FR.1, a BN.1 descendant (which is a BA.2.75 descendant)—has a 1-nucleotide insertion at the same location. This causes a frameshift *identical* to the 2-nuc deletion in XBC.1.6, the only difference being an extra F residue in FR.1. 11/ Image
So the new, frameshifted ORF7b is about ~75% as long as the old version. But the amino acid composition drastically differs, particularly in the number of polar vs nonpolar AA residues. Post-frameshift, 7 of the first 14 AA are polar vs 0/14 in the old ORF7b. 12/ Image
But 10 of the last 11 AA residues of the original ORF7b are polar/hydrophilic, & the new, truncated ORF7b lacks these altogether. I think it's safe to say these are two very different proteins. 13/ Image
But what does it all mean? The fact that two of the most competitive non-XBB variants have both stumbled on the same new protein through different routes suggests it may be beneficial in some way, perhaps throwing a spanner in the works of our immune response. 14/
Or the new ORF7b could be a junk protein w/no function. ORF7b likely isn't important enough to have a major impact. But I think this illustrates the sort of evolutionary surprises that are possible. Even as some are erased (ORF8), entirely new proteins can be created. 15/
Indeed at least one already has! It resulted from a 3-nucleotide mutation in N, creating a new TRS-B & leading to the production of the N* protein, which has been shown to interfere with the immune response and increase viral loads. 16/ nature.com/articles/s4146…
N* is now universal except for in Deltacrons like the XBC lineage. It's was a major development that hasn't seemed to get the attention it merits. But that would be an entirely different thread. Time to end this one. 17/
As always to the labs, lab workers, and researchers doing the groundwork, without which none of this would be possible. As funding is reduced and sequencing decreases, their work is more important than ever. 18/end

• • •

Missing some Tweet in this thread? You can try to force a refresh
 

Keep Current with Ryan Hisner

Ryan Hisner Profile picture

Stay in touch and get notified when new unrolls are available from this author!

Read all threads

This Thread may be Removed Anytime!

PDF

Twitter may remove this content at anytime! Save it as PDF for later use!

Try unrolling a thread yourself!

how to unroll video
  1. Follow @ThreadReaderApp to mention us!

  2. From a Twitter thread mention us with a keyword "unroll"
@threadreaderapp unroll

Practice here first or read more on our help page!

More from @LongDesertTrain

Apr 25
About 1 month after this monster BQ.1.1 appeared, an even more extreme sequence has shown up in Alberta. Like the BQ, it has 50 private spike mutations, but it also has >40 AA mutations elsewhere in the genome. 1/6 Image
They include the full panoply of NSP3, NSP12, & N muts I've written about previously. ORF1a:S4398L is the most common mutation in the 4395-4398 region, this has ∆S4398, a rarity also seen in a few other extremely divergent seqs w/this constellation. 2/6 Image
In a theme that's become familiar, it's added two spike NTD glycans, N30 (via F32S) and N155 (via S155N+F157S).
Another chronic-infection leitmotif (first noted by @SolidEvidence): reversions to common or consensus residues in related Bat-CoVs, including SARS-1. 3/6 Image
Read 6 tweets
Apr 10
A fascinating SARS-CoV-2 sequence was recently uploaded—collected from a dog in Kazakhstan in July 2022.

Usher places the seq 1 nuc mut from the Wuhan ref seq—C21846T/S:T95I—i.e. pre-D614G. Could this seq somehow have a close connection to the first days of the pandemic?
1/19 Image
Of the sequences near this one on the tree, all are low-quality & clearly bad BA.1 or Delta sequences. The only genuine one is from the UK, collected April 2020. So it's likely even S:T95I was not inherited.

This sequence has several fascinating aspects. 2/ Image
(This all assumes the sequence is accurate and that C241T & C14408T (ORF1b:P314L) are genuinely absent. Its mutational characteristics make me certain this is a good sequence, though it's not impossible there's dropout not indicated hiding C241T and/or C14408T.) 3/
Read 19 tweets
Mar 12
Do you remember BA.3—the weakling cousin of BA.1 & BA.2 that seemed to take the worst from each & had weaker ACE2 binding than even the ancestral Wuhan Virus?

After 3 years, BA.3 is back.

And it is transmitting.

Who saw this coming?
1/13 Image
While the full extent of the new BA.3’s spread is not known, it’s been detected in 2 different South African regions through regular (not targeted) surveillance by @Dikeled61970012, @Tuliodna, & the invaluable South African virology community.
2/13
github.com/cov-lineages/p…
After nearly 3 years of intrahost evolution in a chronically infected person, the new BA.3 is almost unrecognizable. It has ~41 spike AA substitutions (4 of which are 2-nuc muts) to go with 14 AA deletions (∆136-147+∆243-244). We’ve seen nothing like this since 2023.
3/13 Image
Read 13 tweets
Jan 2
Two quick notes on the state of chronic-infection SARS-CoV-2 seqs

#1) ~3 years after its peak, BA.1 is still showing up in nasal swab seqs—despite reduced surveillance—most recently a mid-late Dec BA.1 from Nebraska.

#2) Chronic JN.1 seqs now more common, w/1 peculiarity

1/12
While BA.1 still show up semi-regularly, pre-Omicron seqs are much rarer. Why? I think there are four major reasons, two obvious & two less obvious.

A) Time.
This one’s obvious: Over time, some chronic infections are cleared, while in other cases, the host dies.

2/12
B) Number of infections.

BA.1 infected more people, more quickly than any previous variant. More infections = more chances to establish long-term infection.
3/12 Image
Read 12 tweets
Dec 23, 2024
Fantastic review on chronic SARS-CoV-2 infections by virological superstars Richard Neher & Alex Sigal in Nature Microbiology. I’ll do a short overview, outline a couple minor quibbles, & defend the honor of ORF9b w/some stats & 3 striking sequences from the past week.
1/64 Image
First, let me say that this is well-written, extremely readable, and accessible to non-experts, so you should go read the full paper yourself, if you can find a way to access it. (Just realized it’s paywalled, ugh.) 2/64nature.com/articles/s4157…
Neher & Sigal focus on the 2 most important aspects of SARS-CoV-2 persistence: its relationship to Long Covid (including increased risk of adverse health events) & its vital importance to the evolution of SARS-CoV-2 variants. I’ll focus on the evolutionary aspects.
3/64 Image
Read 64 tweets
Dec 6, 2024
In SARS-2 evolution, amino acid (AA) mutations get the lion’s share of attention—& rightfully so, as noncoding & synonymous nucleotide muts—which cause no AA change‚ are mostly inconsequential. But there are many exceptions, including a possible new one I find intriguing. 1/30
I’ll discuss four categories of such “silent” mutations, two of which might be involved in the recent growth of one synonymous mutation.

#1. Kozak sequence changes
#2. Secondary RNA structure
#3. TRS destruction/improvement
#4. TRS creation 2/30
Maybe the single most remarkable example of convergent evolution in SARS-CoV-2 involves noncoding mutations: the multitude of muts in major variants that have pulverized the nucleocapsid (N) Kozak sequence.
I wrote about this below & a few other 🧵s 3/
Read 33 tweets

Did Thread Reader help you today?

Support us! We are indie developers!


This site is made by just two indie developers on a laptop doing marketing, support and development! Read more about the story.

Become a Premium Member ($3/month or $30/year) and get exclusive features!

Become Premium

Don't want to be a Premium member but still want to support us?

Make a small donation by buying us coffee ($5) or help with server cost ($10)

Donate via Paypal

Or Donate anonymously using crypto!

Ethereum

0xfe58350B80634f60Fa6Dc149a72b4DFbc17D341E copy

Bitcoin

3ATGMxNzCUFzxpMCHL5sWSt4DVtS8UqXpi copy

Thank you for your support!

Follow Us!

:(