>> For time, I think we'll have to move on.
So our final presenter before lunch is Carolyn MacHamer.
Carolyn is professor of cell biology
and as an expert on coronaviruses, she has been particularly
busy these days.
Today she's going to talk with us about her research
and what we know about the basic biology of these viruses.
>> Okay, thank you very much.
We need to,
I have little trouble screen sharing here.
Sorry about this.
>> Instructor: Is the screen share icon at the bottom,
is it not working or?
>> It looks like I have some privacy thing on my,
I'm using a different computer which is just stupid.
Let's see if I can.
Anybody know where the,
I'm trying to find my privacy settings
'cause it won't let me share the screen.
>> Instructor: Are you on a Mac or a PC?
>> Yeap, I'm on a Mac.
>> Instructor: So usually you have to allow privacy
by going into the, pulling down the Apple menu
going into the system preferences,
and then once you're in system preferences, there's a panel
that... >> Yeah, I've got the panel,
I don't see-- >> Really.
No, no, that is mine.
And then, so you're looking at security and privacy.
>> Carolyn: Yes.
>> Instructor: And
usually it's under.. >> Oh, wait, here we go.
>> Instructor: Privacy's mean--
>> Carolyn: It's coming up to screen recording
but that's kind of weird. >> That's okay.
>> Okay. >> Yeah, you're recording this,
that may be why it's--
>> Carolyn: Okay, there we go, sorry about this.
Luckily my presentation is pretty short.
Okay, here we go.
>> Instructor: Perfect, I can see that, clear.
>> Sorry, (laughing) okay.
So I imagine
that, many of you-- >> Yeah (mumbles).
>> Can you hear me okay?
>> Instructor: Can hear you but now we're seeing your notes
as opposed to your slideshow so you'll wanna switch,
you go up to the top.
Go ahead and start the slideshow.
>> I wanna do my Presenter View.
Okay, well, we'll just do that (mumbles).
>> Yeah. >> That's fine.
How's that? >> (mumbles) You got it.
>> Okay, sorry about that everyone.
so I imagine some of you haven't heard the word coronavirus
until this January of this year
but I've been fascinated by these viruses
for about 35 years now.
And I should say at the onset, that
our work doesn't directly impact precision medicine,
which is the theme of this boot camp
but it illustrates, I think, the foundational work
that's required to understand the disease.
So first, let's just look at the fact that there are many
kinds of viruses that infect humans.
They can have RNA genomes, they can have DNA genomes,
these genomes are wrapped by different types of proteins
and then they can have envelopes surrounding them
and this is like a fatty lipid membrane
derived from the host.
And what's important here is that these viruses
have very streamlined genomes.
And that means they depend on the host machinery
for their replication and their and all of the things
they do to the cells.
So many, many mechanisms for hijacking cells exist
by these different viruses, probably at least as many
as there are types of viruses.
Now in terms of coronaviruses, the diseases,
they infect all vertebrates and generally cause
mild respiratory or gastrointestinal disease,
including up to 30% of the common cold in humans.
But in December of 2002, the severe acute
respiratory syndrome coronavirus emerged
with 10% mortality, so pretty serious.
In 2012, the Middle East Respiratory Syndrome virus appeared
with 35% mortality and now in January 2020,
of course we have COVID-19 caused by SARS coronavirus 2
and importantly, we don't have any approved vaccines
or therapeutics for any of these
serious human coronaviruses.
Now, these viruses are transmitted to humans zoonotically
which means from an animal and it looks like bats
are the main reservoir for most animal coronaviruses
and they can pass often through an intermediate host
before infecting humans, although we don't yet quite know
how SARS coronavirus 2 was transmitted to humans.
In spite of all the havoc that SARS coronavirus 2 is
causing around the world, the structure is quite simple.
This cartoon shows a virion with an RNA genome,
the RNA is about 30,000 bases long.
And it's wrapped by a protein called,
endo nucleocapsid and enclosing that genome
is an envelope made up of a membrane that has three
other proteins in it.
The M protein is the most abundant and scaffolds assembly.
The small protein E is not very abundant in the virus
and I'll tell you more about that in a moment,
and then the spike or S protein which protrudes
quite a distance from the envelope and interacts
with the host cell by binding it and allowing entry
of the virus and that S protein also gives the
characteristic corona-like structure seen in this
electron micrograph that gives
the coronavirus family its name.
This is the genome, a diagram of the genome of
this SARS coronavirus 2 and amazingly, it has just
16 genes that encode for 29 proteins,
and they're shown here.
Now just to put that in perspective, your cells have about
at least 20,000 genes.
So here's this virus causing this huge pandemic
that has this very limited amount of genetic information.
The first part of the genome codes for proteins
that are important for replicating
the genome and transcribing the messages.
The structural proteins I mentioned are encoded
in this part of the genome, along with what we call
accessory proteins, which mostly are thought to interact
with the innate immune system and try to block that.
Now, importantly, enveloped viruses, all enveloped viruses
use a secretory pathway in the cell.
This is a cartoon of the secretory pathway.
This is a pathway used by all host proteins
that are gonna be secreted out of the cell like antibody
or insulin, for example, or for proteins that are gonna be
inserted here at the plasma membrane of the cell,
such as receptors and enveloped viruses use this pathway
for synthesizing their membrane proteins just as well
the cell doesn't know that there's any difference.
It's making these proteins because it looks like
a normal cell message to be synthesized.
So the first, the place where these this group of proteins
are synthesized is called the endoplasmic reticulum.
The next compartment along the pathway is called
the Golgi complex.
This is a, has a funny name, it was named after
an Italian neuroanatomist, who discovered the organelle
in the late 1800s.
And then, these things move in these vesicles
to be transported to the cell surface.
So, you can imagine a virus like influenza,
making these membrane proteins, the membrane proteins
come together, they bind to the genomes, the virus buds out
taking a little piece of the plasma membrane,
now the virus is released and is ready to go on
and infect a new cell.
The Corona viruses don't do this simple or pathway at all,
they have a very unusual way of assembling in the cell.
This is just a cartoon showing an overview of the
coronavirus infection cycle.
That S protein binds a cell receptor that allows entry
of the virus, the genome looks like any other messenger RNA
to the cell and it's translated to form those
first two thirds of the genome proteins
that are important for replication and transcription.
Once these structural protein RNAs are made,
the nucleocapsid or N protein is synthesized
in the cytoplasm to wrap the new genomes whereas these
membrane proteins go through this pathway,
I described, the so called secretory pathway.
And they actually do not go all the way to the cell surface
they actually congregate together in this Golgi complex
compartment for assembly.
And our work over the years has studied these later steps
the assembly and egress of virus from the cells
because this is not the most efficient method
for release of virions.
So here's just looking at a little more carefully at this.
So we have here the three envelope proteins
and they're made in the secretory pathway coming together
in this early compartment of the Golgi
and what you see here in this enlargement is that
these proteins interact with each other
and interact with the nucleocapsid wrapped RNA genome
and form a bud instead of out of the cell,
they form into the lumen,
the inside of this Golgi compartment.
And then you have these enveloped variants that have to
get through the cell and get out of the cell.
And this assembly pathway really presents several challenges
for the virus.
As you can see here, this is an electron micrograph
section through an infected cell and the Golgi stacks
as I said they're, they look kind of like a stacks
of pancakes and that's why we've been fascinated by
the structure function of this organelle.
I should also say that that Golgi complex, I believe is the
true post office of the cell, unlike sort of Ken
Witwer's analogy of the extracellular vesicles,
that's sort of the postal system and whereas this is the
post office where sorting and processing of cargo goes on.
Anyway, the challenge is, first of all, the cargo here,
which is the virus is much bigger than the space
between these flattened sets of membranes.
So the organelle has to be dilated to accommodate
the budding virions and then the next challenge
is how these are gonna get out of the cell.
Again, it's a slow and inefficient process,
probably due to the size of the cargo.
So we've been studying this process and wondering
is there a way that we can interfere with it?
And over the years we've studied a protein called
the E protein, this is that small envelope protein
of the virus.
It's only 74 to 124 amino acids
depending on the coronavirus, and we've used
a model coronavirus in our work but we've also studied
the original SARS coronavirus.
And the first function for this little E protein
is in assembly where the E protein either helps
bend the membrane to form the bud and or helps it
undergo scission from the Golgi membrane to allow
these virus particles to be inside the Golgi itself.
But we've also found another interesting role
for the protein and that is in modification
of the secretory system.
And this role requires the E protein that's in the membrane
itself and not incorporated into the virus.
Remember I said this is a very low abundance protein
in the virion, in the virus particle itself
but it's present in pretty high levels in the cells
and it sits in the Golgi membranes
and it through its activity modulates the environment
of this compartment and that allows these virus particles to
exit the cell in an infectious form.
We know that because a mutant of this E protein
that can't do this function, the particles that are released
are damaged and their product, they've run into enzymes
that chew up the proteins and therefore
they're not infectious so this small little protein
has two functions, and the two different functions
depend on different portions of the protein
and I think this is a really nice example of how
these streamlined genomes of the virus can perform
their multitude of functions that they need to.
But the big question here,
and I hope you're thinking about this is why in the world
would a virus want to do this?
What is the advantage of intracellular assembly
with all these challenges that the virus has?
And I wish I could say that we knew the answer to this.
We don't know the answer, we have ideas that we've tested
over the years but clearly, it provides a real advantage
for the virus given that these viruses can mutate
and do it better.
So that's a question that we're really very
still interested in and we just don't know enough
about the basic biology of these viruses
to be able to answer the question yet.
Now, importantly,
the fact that the vaccine, there's not gonna be a vaccine
in the near future and so what about therapeutic approaches?
Well, there's drugs that block the entry phase.
There's drugs that interfere with replication
of the virus, but nothing yet that we know of
that interferes with assembly or release.
And part of the problem here is because
this part of the pathway hasn't been well studied.
And if there's one good thing
to come out of the COVID-19 pandemic,
I think it's that many, many cell biologists
have become very interested in these viruses,
and now want to study this process, this assembly
and release process, and hopefully with sustained funding,
we'll be able to get another approach to interfering
with coronaviruses because clearly,
pandemics in the future are certainly not
impossible to imagine.
I'll just close with thanking a number of trainees,
students, postdocs, undergraduates,
who have been involved in the various
aspects of coronavirus biology, including these,
all of these graduate students and postdocs here who
were involved in the latter part of our work,
and our funding sources, thank you.
>> Instructor: Okay, great, thank you very much, Carolyn,
for that terrific overview.
There aren't any questions that have come in just yet
and we're running over time so I think what we're going
to do now is just go ahead and break for lunch.