Tom Rapoport (Harvard, HHMI) 1: Organelle Biosynthesis and Protein Sorting
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- Опубліковано 6 чер 2024
- www.ibiology.org/cell-biology...
Eukaryotic cells have many different membrane-bound organelles with distinct functions and characteristic shapes. How does this happen? Dr. Tom Rapoport explains the important role of protein sorting in determining organelle shape and function.
In his first talk, Dr. Tom Rapoport explains that eukaryotic cells contain many membrane-bound organelles each of which has a characteristic shape and distinctive functions that are carried out by specific proteins. Most proteins are made in the cytosol but must move to different cellular destinations. Protein sorting is determined by signal sequences on the proteins that act as “zip codes”. Many proteins sort first to the endoplasmic reticulum (ER) before moving to other intracellular organelles or the plasma membrane. Rapoport explains that as a protein is translated, its signal sequence causes the nascent protein to insert into the Sec61 channel on the ER membrane. The polypeptide segment following the signal sequence will then be translocated across the membrane. Solving the structure of Sec61 channel allowed Rapoport’s lab to understand how proteins, which are typically hydrophilic, can be transported across a lipid membrane. It also helped them determine how Sec 61 differentiates between secreted proteins which need to be released into the ER lumen and transmembrane proteins which need to be anchored in the ER membrane. This improved knowledge of protein sorting helps us to better understand how organelles are formed and how they function.
The ER is a vast network that includes different domains with different functions. The rough ER consists of sheets with associated ribosomes and is involved in protein translation. The smooth ER consists of tubules and is important for lipid synthesis and Ca2+ transport. In his second talk, Rapoport explains how his lab identified proteins needed to generate and maintain a tubular ER network. They found two families of proteins that are required to form the high membrane curvature of tubules, and membrane-bound GTPases that fuse the tubules together into a network. The tubule-shaping proteins are also important in forming the edges of the ER sheets. In mammalian cells, however, another set of proteins is required to act as spacers between the membrane sheets. Using ultra-thin section electron microscopy, Rapoport’s lab, in collaboration with others, was able to show that stacked ER sheets are held together by helicoidal membrane connections forming a “parking-garage” like structure.
Speaker Biography:
Dr. Tom Rapoport has been a Professor of Cell Biology at Harvard Medical School since 1995 and a Howard Hughes Medical Institute Investigator since 1997. Prior to joining Harvard, Rapoport was a Professor at the Institute for Molecular Biology in East Berlin, which later became the Max-Delbrück Institute for Molecular Medicine. Rapoport received his PhD from Humboldt University of Berlin.
Rapoport’s research focuses on the understanding how organelles, in particular the endoplasmic reticulum (ER), derives its characteristic shape and performs its specific functions. He has had a long standing interest in how proteins are translocated across organelle membranes. His pioneering research has been recognized with many awards including the Max-Delbrück Medal in 2005, the Sir Hans Kreb Medal in 2007, and the Schleiden Medal in 2011, among many others. Rapoport is a member of the National Academy of Sciences, USA and the German Academy of Sciences, Leopoldina. He is also a Fellow of the American Association for the Advancement of Science (AAAS).
Learn more about Rapoport’s research here:
rapoport.hms.harvard.edu
and here:
www.hhmi.org/scientists/tom-r... - Наука та технологія
Absolutely amazing. I love how he often says, "it's very simple", when describing a system that incorporates many tens of thousands of molecules performing a choreography of miraculous complexity!
Thanks so much Dr Rapoport!
Thank you so much for sharing this! It is wonderfull!
Thank you for good lecture :)
The characterisation of the cell ....internally it's a 3D interwoven structure of two different entities the microtubules and the ER tubes. Seems amazing.
looks like the signal sequence uses a hairpin to pick the lock of the SecY channel protein
This iBiology series is Brilliant. The complexity just defies creation-by-accident.
@Dev Rifter Inanimate stuff, doesn't evolve, and most of the archaea class, over 4 billion years old, are still here, and don't use DNA. They are RNA class users. Nothing is left to evolve.
we need to come up with some way to have like "dry" organelles that we can mix all together to create the constituent cell... or like some way to "bootstrap" simple cells into complex cells with a series of viruses or like turn a prokaryote into a eukaryote by printing a nuclus inside of it
your work is really great, I am fond of your work, I want to know about the molecular mechanics, how molecules move to the target, what makes them move,
i think it is just thermal dynamics no? they will probably sample lots of different positions in space due to diffusion, and be arrested/associate for longer periods of time with their target.
@@lana_del_rei I do not think it is simple as that, I think it is an invisible matrix or lattice, that makes molecules move directed by this invisible matrix, or may a quantum mechanical phenomena take place
wafy Fahim its most likely a mix of thermodynamic and quantum mechanical phenomena, statistical mechanics would be something to look into
@@just_an_empty_sign I think it is not a space-time signal, it is a nonlocal signal, while generated it does its action remotely and instantaneously like quantum entanglement, and the chemicals we measure are the result from this effect, not the cause
@@medicinefuture Wow - so that really turns it all upside down. How do we go about specifying/locating the non-local mechanism? I realise there may be motivational constraints.
All the details of one eukaryotic cell make up a more complex system than the whole macroscopic biological world combined!
Amazing human intellect
Is there some reference somewhere that compares all the known signal peptides, their locations, and their relative efficiencies? I get the impression there multiple localization signals are required, but I'd still like to know their efficiencies.
What about something like a viral membrane fusion protein that has a fusion peptide? It's a continuous series of hydrophobic residues surrounded by more polar or charged residues. How is that expressed without getting stuck in the membrane? They'd seem to be type-II, so maybe the hydrophobic fusion peptide is covered up as soon as it's expressed? I don't know much about how things are expressed, but this seems problematic since membrane fusion proteins are homotrimers. You'd have to trimerize as fast as you express to fully cover the fusion peptide. Does that sound realistic? Is there a better mechanism for the expression a continuous series of hydrophobic residues that doesn't insert into the membrane?
Yes, you can find some known signal peptides in many cell biology textbooks, such as Molecular Biology of the Cell (Garland Science)
Here's an example: imgur.com/DCTMTQS
I'm not sure I understand your other questions, I'm just an undergrad :v A viral membrane fusion protein seems to belong in a membrane, since it causes membrane fusion, so it won't end up in the ER lumen I believe. I don't know much afterward, it probably goes through the Golgi apparatus (?), but since it's meant to be in a virus' membrane, it would go to assemble with the other virus' parts until the cell's lysis happen, where the viruses are free to go infect other cells.
Viral fusion (initial entry) is usually coupled to attachment via another viral protein that attaches to a host cell protein that acts as receptor. So you'll often hear about attachment -entry as a if it were one even though it is composite process. HIV for example has the Env region divided into two major ORFs SU (surface: attachmebt) and TM (transmembrane: fusion) . The general idea is that the process is systematic and coordinated . TM only acts as a fusion iniatir if it gets the proper interaction with SU and sometines even multiple other host proteins and even host cell lipid rafts (little islands on the membrane where particular phospholipids concentrate.)
Sometimes TM proteins transported to the surface act as fusion proteins befire progeny virions bud off fusing cells together (or perhaps this is a specialized pathway.. perhaolps those TMs are unique) giving virus a stealthy way to spread. HIv facilitates the formation of multinucleate giant cells in this manner. Another related topic is endogenous retroviruse genomes incorporated into animal genomes have contributed or have been co-opted to do similar things in host organism biology. Syncitin does this in placental mammals and Arc doe this to facilitate RNA transfer between synapsing neurons. These are co-opted viral fusion proteins
@@patldennis, yeah, but that says nothing about the actual expression and folding of the membrane fusion protein. I know a bit about viral membrane fusion proteins especially human endogenous viral membrane fusion proteins, but my question was how do they express and fold without the fusion peptide getting stuck in the membrane during translation.
My guess is that the fusion peptides actually only insert the side chains of a few residues into membrane rather than having a full series of hydrophobic residues, but I haven't gotten around to actually looking that up. I'm sure if I read a paper with the NMR structure of the fusion peptide in the presence of membranes it'll tell me if that hypothesis is correct or not.
@@TrystynAlxander_PoI My answer was you need to have the the attachment protein coordinated with the fusion pritein in order to initiate the cascade. Without it it's like a gun with its safety on
@@patldennis , maybe I don't understand what you're talking about. To me it sounds like you're talking about a fully formed virus where the viral fusion protein (Env) is already folded. That virus then attaches to the target cell either with a receptor binding domain or a separate viral protein that functions analogously. Along with that attachment interaction the membrane fusion protein then exposes a hydrophobic fusion-peptide that inserts into the target membrane. Then the Env refolds bringing the trans-membrane region and the fusion peptide together for membrane fusion and viral entry. I'm okay with all that, but I'm not asking about that.
I'm talking about when the Env protein is first folding during viral assembly. I'm not entirely sure I understand what you mean when you say "attachment protein" but if you mean the target receptor that's not relevant in this context as the protein is still internal. It's being expressed on the ER. If you mean any partner protein, I'm not sure that's relevant either because the peptide is just coming out of the ribosome. I doubt it can reliably interact with any partner protein and not all Envs have partner proteins. My question is about the very specific circumstance where the fusion-peptide is coming out of the ribosome and is going into the ER. The majority of the Env protein hasn't even been translated into amino-acids at this point.
How is the mRNA 'exported' to the ribosome? I mean, how does the tRNA (that which -- I assume -- transports the mRNA) know to go left or right or straight. And how does it execute whatever degree turn it needs to make at its final destination in order to fit its cargo into the slot at the ribosome,?
tRNA doesnt transport mRNA, it transports aminoacids to the rybozome-mRNA complex to build a protein.
call him tom rapoport cayse he can rapup a report ya know what im sayin
why cant we build the economy around science and scientisfs? instead of workers or capitalists.
You lost me when you started talking about evolution. Math proves it didn't happen, yet you stand there talking about it s if you were there watching. Sorry, but I can't respect that.
Agreed, de-evolution from perfect harmony should be the accepted understanding of our history. Sin destroys.
Math proves it happened, sorry
God you people are so fucking dumb lmfao