Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

New protein-sensing mechanism discovered

01.08.2019

In a stunning discovery, molecular biologists from the University of Konstanz and ETH Zurich have been able to demonstrate that the nascent polypeptide-associated complex (NAC) senses newly synthesized proteins upon birth inside the ribosomal tunnel

New research published in Molecular Cell on 31 July 2019 conducted by researchers from the University of Konstanz’s Collaborative Research Centre 969 “Chemical and Biological Principles of Cellular Proteostasis” shows that the nascent polypeptide-associated complex (NAC) acts as a major protein identifying and, possibly, sorting device inside the cell.


Ribosome binding of NAC is mediated by a ribosome binding regulatory arm (N-αNAC, blue) and a translation sensor domain (N-βNAC, green). N-βNAC senses short nascent chains already deep inside the ribosomal tunnel close to the peptidyl-transferase centre (orange) where amino acids are assembled into proteins. The tunnel-sensing activity of NAC is believed to orchestrate general cotranslational protein folding and transport processes in the cell.

Copyright: Martin Gamerdinger


The University of Konstanz team, from left to right: Nadine Sachs, Martin Gamerdinger, Renate Schlömer, Elke Deuerling, Carolin Sailer, Stefan Kreft

University of Konstanz

Working closely with Professor Nenad Ban, an expert for resolving ribosomal structures from ETH Zurich, the team led by Professor Elke Deuerling and Dr Martin Gamerdinger from the University of Konstanz’s Department of Biology – including co-workers Annalena Wallisch, Dr Stefan Kreft, Nadine Sachs and Renate Schlömer as well as Junior Professor Florian Stengel and doctoral researcher Carolin Sailer – has discovered that NAC inserts the N-terminal domain of its β-subunit (N-βNAC) deep into the ribosomal tunnel to sense substrates directly upon synthesis and to escort growing polypeptides to the cytosol.

“No other factor we know does that, which is why we were so utterly surprised by our findings. Although NAC was discovered as long as 25 years ago, we are only now beginning to understand how crucial it is for proper cell function. Our study shows that, besides acting as a chaperone both on and off the ribosome, NAC is also able to recognize nascent polypeptide chains deep inside the ribosomal tunnel”, says Professor Elke Deuerling, lead author on the study and Professor of Molecular Microbiology at the University of Konstanz.

“We already knew NAC to transiently interact with translating ribosomes. But we did not understand how exactly NAC interacts with the ribosome and with nascent substrates to regulate protein folding and transport to the endoplasmic reticulum (ER), which is essential for organismal viability”.

The researchers performed biochemical, genetic and structural analyses in the model system C. elegans to attain a more detailed understanding of how NAC identifies and sorts nascent polypeptide chains inside the ribosomal tunnel. “Until quite recently, we assumed that the earliest point of interaction between ribosome-associated factors such as chaperones, enzymes and transport proteins was when the nascent polypeptide chains exit the ribosomal tunnel”, explains Dr Martin Gamerdinger, first author on the study alongside Kan Kobayashi, formerly of ETH Zurich and currently an assistant professor at the University of Tokyo.

“Usually, at that point, the chains have a length of about 40 amino acids. What we have discovered is that NAC binds to nascent chains as short as ten amino acids or even shorter, and it is doing it inside the tunnel. This makes NAC the very first factor to contact newly synthesized proteins. We even suspect it to be able to sense when the first two amino acids of a nascent protein connect with each other”.

As the researchers have been able to show using a combination of cryo-electron microscopy, mass spectrometry and biochemical analyses, including a series of site-specific crosslink experiments, NAC inserts the positively charged and highly flexible N-terminal domain of its β-subunit (N-βNAC) into the ribosomal tunnel, which is for the most part lined by negatively charged ribosomal RNA.

“What our study demonstrates is that NAC is able to sense translation activity inside the tunnel and, more importantly, that it is able to sense the character of the proteins that are being synthesized. At least that is our current hypothesis”, says Elke Deuerling.

Once they exit the ribosomal tunnel, nascent protein chains can continue down a range of different biogenesis pathways: Some are passed on to other factors that escort these chains to their intended destinations somewhere else inside the cell. Some are modified by enzymes, others require chaperone support to attain their native structural fold.

As Martin Gamerdinger comments: “If what we are assuming about the early sensing-mechanism of NAC is correct, then this complex is the single most important protein sorting mechanism that we know of. It would explain how cells manage the complex processes and reactions that take place in connection with nascent polypeptide chains once they exit the ribosomal tunnel”. Accordingly, what the researchers plan to verify next is whether the N-βNAC domain can identify the character of nascent proteins inside the ribosomal tunnel and how it prompts them to enter the correct protein biogenesis pathways.

“What we further found is that NAC acts as a molecular filter, preventing inactive ribosomes or ribosomes in the early translational stages from interacting with the translocon of the ER, i.e. with the complex that transports nascent polypeptides with a targeting signal sequence into the endoplasmic reticulum. Unregulated ribosome-translocon interactions could lead to the wrong proteins entering the endoplasmic reticulum on the one hand, and to depletion of protein factors that are in fact needed elsewhere on the other”, says Elke Deuerling. “NAC is thus responsible for making the various steps involved in protein biogenesis much more efficient and specific”.

While the N-βNAC domain seems to be responsible for sensing and possibly for sorting nascent polypeptide chains, another NAC domain, N-αNAC, interacts with the β-domain and with itself in order to regulate NAC activity on ribosomes. “This, too, is something that we did not know about before”, explains Martin Gamerdinger. “Without N-αNAC, NAC would bind too strongly to the ribosome, interfering with the essential protein translation processes taking place there. We have yet to understand how exactly this auto-inhibitory function of NAC works, but what seems clear is that N-αNAC downregulates ribosome binding”. As in vivo experiments with C. elegans clearly showed, worms expressing a NAC variant that lacks the auto-inhibition and shows enhanced ribosome binding were developmentally delayed due to reduced protein synthesis rates and impaired translation, clearly showing defects caused by NAC-ribosome misregulation.

Facts:
• International team of researchers from the University of Konstanz and ETH Zurich identifies nascent chain recognition mechanism deep inside the ribosomal tunnel that is driven by the essential eukaryotic chaperone NAC (nascent polypeptide-associated complex).
• NAC tunnel-sensing activity is essential for organismal viability and critical for the regulation of protein transport to the endoplasmic reticulum; major implications for general understanding of protein translation and maturation in cells.
• Original publication: Martin Gamerdinger, Kan Kobayashi, Annalena Wallisch, Stefan G. Kreft, Carolin Sailer, Renate Schlömer, Nadine Sachs, Ahmad Jomaa, Florian Stengel, Nenad Ban, Elke Deuerling. Early scanning of nascent polypeptides inside the ribosomal tunnel by NAC. Molecular Cell. 31 July 2019. DOI: https://doi.org/10.1016/j.molcel.2019.06.030 (DOI becomes active shortly after 11:00 US Eastern Time, after the embargo has lifted).
• The research carried out at the University of Konstanz was supported by the Collaborative Research Centre 969 “Chemical and Biological Principles of Cellular Proteostasis”, funded by the German Research Foundation (DFG) since 2012.

Note to editors:
Images are available for download here:

Image 1: https://cms.uni-konstanz.de/fileadmin/pi/fileserver/2019/Bilder/new_protein-sens...
Caption: Ribosome binding of NAC is mediated by a ribosome binding regulatory arm (N-αNAC, blue) and a translation sensor domain (N-βNAC, green). N-βNAC senses short nascent chains already deep inside the ribosomal tunnel close to the peptidyl-transferase centre (orange) where amino acids are assembled into proteins. The tunnel-sensing activity of NAC is believed to orchestrate general cotranslational protein folding and transport processes in the cell.
Copyright: Martin Gamerdinger

Image 2: https://cms.uni-konstanz.de/fileadmin/pi/fileserver/2019/Bilder/new_protein_sens...
Caption: The University of Konstanz team, from left to right: Nadine Sachs, Martin Gamerdinger, Renate Schlömer, Elke Deuerling, Carolin Sailer, Stefan Kreft
Copyright: University of Konstanz

Contact:
University of Konstanz
Communications and Marketing
Phone: +49 7531 88-3603
Email: kum@uni-konstanz.de

Julia Wandt | Universität Konstanz
Further information:
http://www.uni-konstanz.de

More articles from Life Sciences:

nachricht Cancer cachexia: Extracellular ligand helps to prevent muscle loss
25.02.2020 | Leibniz-Institut für Alternsforschung - Fritz-Lipmann-Institut e.V. (FLI)

nachricht The genetic secret of night vision
25.02.2020 | Max-Planck-Institut für molekulare Zellbiologie und Genetik

All articles from Life Sciences >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: High-pressure scientists in Bayreuth discover promising material for information technology

Researchers at the University of Bayreuth have discovered an unusual material: When cooled down to two degrees Celsius, its crystal structure and electronic properties change abruptly and significantly. In this new state, the distances between iron atoms can be tailored with the help of light beams. This opens up intriguing possibilities for application in the field of information technology. The scientists have presented their discovery in the journal "Angewandte Chemie - International Edition". The new findings are the result of close cooperation with partnering facilities in Augsburg, Dresden, Hamburg, and Moscow.

The material is an unusual form of iron oxide with the formula Fe₅O₆. The researchers produced it at a pressure of 15 gigapascals in a high-pressure laboratory...

Im Focus: From China to the South Pole: Joining forces to solve the neutrino mass puzzle

Study by Mainz physicists indicates that the next generation of neutrino experiments may well find the answer to one of the most pressing issues in neutrino physics

Among the most exciting challenges in modern physics is the identification of the neutrino mass ordering. Physicists from the Cluster of Excellence PRISMA+ at...

Im Focus: Therapies without drugs

Fraunhofer researchers are investigating the potential of microimplants to stimulate nerve cells and treat chronic conditions like asthma, diabetes, or Parkinson’s disease. Find out what makes this form of treatment so appealing and which challenges the researchers still have to master.

A study by the Robert Koch Institute has found that one in four women will suffer from weak bladders at some point in their lives. Treatments of this condition...

Im Focus: A step towards controlling spin-dependent petahertz electronics by material defects

The operational speed of semiconductors in various electronic and optoelectronic devices is limited to several gigahertz (a billion oscillations per second). This constrains the upper limit of the operational speed of computing. Now researchers from the Max Planck Institute for the Structure and Dynamics of Matter in Hamburg, Germany, and the Indian Institute of Technology in Bombay have explained how these processes can be sped up through the use of light waves and defected solid materials.

Light waves perform several hundred trillion oscillations per second. Hence, it is natural to envision employing light oscillations to drive the electronic...

Im Focus: Freiburg researcher investigate the origins of surface texture

Most natural and artificial surfaces are rough: metals and even glasses that appear smooth to the naked eye can look like jagged mountain ranges under the microscope. There is currently no uniform theory about the origin of this roughness despite it being observed on all scales, from the atomic to the tectonic. Scientists suspect that the rough surface is formed by irreversible plastic deformation that occurs in many processes of mechanical machining of components such as milling.

Prof. Dr. Lars Pastewka from the Simulation group at the Department of Microsystems Engineering at the University of Freiburg and his team have simulated such...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

VideoLinks
Industry & Economy
Event News

70th Lindau Nobel Laureate Meeting: Around 70 Laureates set to meet with young scientists from approx. 100 countries

12.02.2020 | Event News

11th Advanced Battery Power Conference, March 24-25, 2020 in Münster/Germany

16.01.2020 | Event News

Laser Colloquium Hydrogen LKH2: fast and reliable fuel cell manufacturing

15.01.2020 | Event News

 
Latest News

Turbomachine expander offers efficient, safe strategy for heating, cooling

25.02.2020 | Power and Electrical Engineering

The seismicity of Mars

25.02.2020 | Earth Sciences

Cancer cachexia: Extracellular ligand helps to prevent muscle loss

25.02.2020 | Life Sciences

VideoLinks
Science & Research
Overview of more VideoLinks >>>