Archive for March 27th, 2014

Giant Zombie Killer Virus Rises From Its 30 000 Year Grave To Kill Us All! Or Not?

27 March, 2014

I am not a fan of “Science By Hype”, which I think I have made abundantly clear via Virology News and elsewhere. Thus, I pour scorn on the “We found a structure which will lead to an AIDS vaccine”, and “We found an antibody that will cure AIDS” type of articles, WHILE at the same time, appreciating the ACTUAL science behind the hype.

If there is any, of course.

Which is why I am torn, on the subject of a giant DNA virus purportedly found in 30 000 year-old Siberian permafrost. I am also a fan of zombies, hence the title. But seriously, now: here we are, with news media and semi- and fully-serious science mags all hailing the description in PNAS, no less, of “Pithovirus sibericum“.  A giant virus, wakened from a 30 000 year sleep in Siberian permafrost, by the kiss of an amoeba. OK, by infecting an amoeba, but you see where I’m going here. Pithovirus_sibericum__Researchers_Resurrect_30_000-Year-Old_Giant_Virus___Biology___Sci-News_com So here we are, with an article from Sci.news.com, trumpeting the discovery.  And there’s more:

“The findings have important implications in terms of public health risks related to the exploitation of mining and energy resources in circumpolar regions, which may arise as a result of global warming. “The re-emergence of viruses considered to be eradicated, such as smallpox, whose replication process is similar to Pithovirus, is no longer the domain of science fiction. The probability of this type of scenario needs to be estimated realistically.””

Yeah.  Rii-ii-ght.  Giant viruses are going to erupt from the permafrost and kill us all!  Really??

No.

Curtis Suttle, he of oceanic metaviromes fame, is quoted as saying the following, in Ed Yong’s Nature blog:

“…people already inhale thousands of viruses every day, and swallow billions whenever they swim in the sea. The idea that melting ice would release harmful viruses, and that those viruses would circulate extensively enough to affect human health, “stretches scientific rationality to the breaking point”, he says. “I would be much more concerned about the hundreds of millions of people who will be displaced by rising sea levels.””

Amen!  In other words, just because there ARE revivable viruses in permafrost – itself no new thing, BTW – does NOT mean they will harm humans. Think about this a moment: something locked away under the surface of the ground for 30 000+ years has to SURVIVE, first; second, it has to INFECT humans if it is to cause any harm. And what evidence do we have that anything found in Siberian permafrost can do that?

None.  None whatsoever.

Think again: how many humans, and how many mammals with virus that could infect humans, were there around on the Siberian plains 30 000 years ago?

Precious few.

And what likelihood is there that any viruses that COULD infect humans, got preserved? Vanishingly small. So what COULD get released from said permafrost, as it melts with inexorable global warming? Well, phages: lots and lots of phages.

Then some plant viruses, maybe: there have been previous reports of Tomato mosaic virus found in 1999 in glacial ice from Greenland, that was between 500 – 140 000 years old – that was also supposed to be a threat, as it escaped from melting icecaps.

To tomatoes, possibly.  If they grew in seawater.

But there’s more: here we have “New Deadly Flu Viruses Reemerge from Melting Ice“, from 2006.  Here we have

“An international team [that] found flu viruses in the ice of Siberian lakes, fact that warns about the possibility that global warming may release germs locked in glaciers for decades or even centuries.”

Yah. Right.  But at the same time, considerably more worthy of alarm than Pandoraviruses. Because what our worthy French colleagues did NOT do, in their report in PNAS, was see what ELSE was in their permafrost samples. Seriously: they trawled melting ice from a core sample with amoebae ONLY.

This is the equivalent of the 2nd year prac I used to do, when we made students screen water obtained from the environment with E coli to see if they could amplify coliphages out of it.  Why did they not do a metagenomic sequence trawl, after filtering out bits of mammoth crap and cockroaches and bits of twigs??  What did they MISS?  HBVs that infected Denisovans?  And are we SURE that the virus came from that long ago?  Has the ice really remained frozen all that time – and is there not the possibility that water didn’t percolate down through cracks and pores in the permafrost, carrying the virus with it, from a more clement environment on the surface??

OK, OK, so it’s a great find, and reasonably worthy of SOME hype.  BUT: it is NOT a harbinger of doom, because most viruses will NOT survive 30 000 years worth of entombment in ice, and in any case, would NOT infect humans even if they did. AND I hate the name: “Pithovirus sibericum“?  Really??  Viruses are not named like that!  Except by French folk who find these strange “amphora-shaped” viruses, apparently.

The Assembly Pathway of an Icosahedral Single-Stranded RNA Virus Depends on the Strength of Inter-Subunit Attractions

27 March, 2014

See on Scoop.itVirology News

The strength of attraction between capsid proteins (CPs) of cowpea chlorotic mottle virus (CCMV) is controlled by the solution pH. Additionally, the strength of attraction between CP and the single-stranded RNA viral genome is controlled by ionic strength. By exploiting these properties, we are able to control and monitor the in vitro co-assembly of CCMV CP and single-stranded RNA as a function of the strength of CP–CP and CP–RNA attractions. Using the techniques of velocity sedimentation and electron microscopy, we find that the successful assembly of nuclease-resistant virus-like particles (VLPs) depends delicately on the strength of CP–CP attraction relative to CP–RNA attraction. If the attractions are too weak, the capsid cannot form; if they are too strong, the assembly suffers from kinetic traps. Separating the process into two steps—by first turning on CP–RNA attraction and then turning on CP–CP attraction—allows for the assembly of well-formed VLPs under a wide range of attraction strengths. These observations establish a protocol for the efficient in vitro assembly of CCMV VLPs and suggest potential strategies that the virus may employ in vivo.

 

Ed Rybicki‘s insight:

I do love it when a paper is published that could have been done pretty much any time in the last 40 years – and with one of my favourite viruses, that I played with a LOT back there before 1980.

Ultracentrifugation, pH meters, ionic strength determinations, EM…all tried and true, and used 40+ years ago. OK, they also used cloned BMV RNA 1 cDNA, and did 3-D image reconstruction from EMs, but hey, they needn’t have done that!  Nice, straightforward physicochemical studies, on a well-characterised virus, with good, simple conclusions. 

Namely, that assembly of the virus is NOT just a simple mix-CP-and-RNA-and-it-will-happen, but that it depends upon both pH, for modulating ionic interactions,and ionic strength for modulating ionic interactions AND the "hydrophobic effect", as we used to know it.

While their conclusions are relevant for assembly of heat- and nuclease-resistant nano particles in vitro, I wonder if they are physiologically relevant: if "correct" assembly depends upon first, turning on CP-RNA attraction (ionic strength shift), and second, turning on CP-CP attraction (pH shift) – where in the cell does that happen?

In their own words, "It is generally accepted that the cytoplasm of plant cells is maintained near neutral pH with ionic strength of approximately 0.1 M. Our in vitro results show that these conditions are insufficient for nucleocapsid formation in the absence of cellular host factors."

Yeeee-ee-eesssss…precisely. What happens in the cell? The answer could lie in the one thing they don’t report, but that some of the heroes of my distant youth – people like JB Bancroft and Thom Hohn, both quoted (from 1970 and 1969 respectively) in this paper, DID do. Namely, investigate what happens at different CP and RNA concentrations, at constant pH and ionic strength.

You see, it was shown 30+ years ago – and I have been lecturing on it since then – that CP and RNA for viruses like BMV / CCMV and MS2 form different complexes with their cognate partners at different molecular ratios. That is, at low CP:RNA ratios, a high-affinity complex is formed, which is basically a ribonucleoprotein complex without structure. Increasing the CP:RNA ratio for both MS2 and CCMV, as I recall (maybe Dick Verduin was involved with CCMV), results in further lower-affinity association of CP with both RNA and already-bound CP – which acts as a nucleation complex – to result in full capsid assembly.

I note that the process in both cases was shown to be specific, for low CP:RNA ratios: that is, it was cognate CP and RNA doing the high affinity nucleation complex formation.

And these guys deliberately used a heterologous RNA…albeit one from a related virus, but still: what would have happened if they’d used CCMV RNA?

Still – great paper, taking me back to when I wrote an essay on "Assembly of Spherical Plant Viruses" in my Honours year in 1977, quoting quite a few of the same references these folk did. Ah, simpler times…B-)

See on www.sciencedirect.com