How many rings does the human nuclear pore complex in "Nature" have?

The model of the human nuclear pore complex depicts the major proteins that make up the tricyclic ring of the pore
.

CR = cytoplasmic ring, IR = inner ring, NR = nucleoplasmic ring

From top to bottom: the cytoplasmic ring is blue and yellow; the inner ring is orange and pink; the nucleoplasmic ring is light blue and gold
.

The researchers collected a more complete picture of a structure by directly studying the nuclear pore complex inside the cell
.

The environment is very important
.

This is true for many aspects of life, including the tiny molecular machines that perform important functions in our cells

Scientists often purify cellular components, such as proteins or organelles, in order to examine them individually
.

However, a new study published in the journal Nature on October 13, 2021 suggests that this approach may completely change the problematic ingredients

The researchers devised a method to study a huge doughnut-shaped structure called the nuclear pore complex (NPC) inside the cell
.

Their results showed that the size of the pores was larger than previously thought, which emphasized the importance of analyzing complex molecules in the natural environment

"We have shown that the cellular environment has a significant impact on large structures like NPC, which we did not anticipate when we started," Thomas Schwartz, a professor of biology at the Massachusetts Institute of Technology and co-senior author of the study.
Schwartz) said
.

"Scientists usually think that macromolecules are stable enough to maintain their basic properties inside and outside the cell, but our findings subvert this hypothesis

In eukaryotes like humans and animals, the DNA of most cells is stored in a circular structure called the nucleus
.

The organelles are protected by the nuclear membrane, which is a protective barrier that separates the genetic material in the nucleus from the thick liquid that fills the rest of the cell

The first author of the study, Anthony Schuller, a former MIT postdoc, compared NPC to the gate of a stadium
.

He explained: "If you want to enter the game, you have to show your ticket and pass through one of the doors

A closer look at the nuclear pore complex

By human standards, NPC may be small, but it is one of the largest structures in a cell
.

It is composed of about 500 proteins, which makes its structure difficult to resolve

Together with researchers at the University of Zurich, Schuller and Schwartz used two cutting-edge methods to solve the pore structure: cryo-FIB milling and cryo-electron tomography (cryo-ET)
.

The whole cell is too thick to be seen under the electron microscope
.

But the researchers used MIT's cryo-FIB device to slice frozen colon cells into thin layers
.
In the process, the team captured the cross-section of the cell containing the NPC instead of simply observing the NPC in isolation
.

"The amazing thing about this method is that we hardly do anything with the cells," Schwartz said
.
"We did not disturb the internal structure of the cell
.
This is a revolution
.
"

The image that the researchers saw under the microscope was very different from the existing description of NPC
.
They were surprised to find that the innermost ring structure forming the central channel of the pore was much wider than previously thought
.
When it is left in the natural environment, the pores open up to 57 nanometers, resulting in a 75% increase in volume compared to previous estimates
.
The team was also able to take a closer look at how the various components of the NPC work together to define the size and overall structure of the pores
.

"We have shown that the cellular environment affects the NPC structure, but now we have to figure out how and why," Schuller said
.
He added that not all proteins can be purified, so the combination of cryo-ET and cryo-FIB will also help to examine various other cellular components
.
"This dual approach opens everything up
.
"

"This paper is a good illustration of the technological advancement.
In this example, the cryo-electron tomography scan of human cells with low-temperature focused ion beam milling provides a new image of the cell structure," Professor of Biochemistry at Achen University of Technology, Germany Wolfram Antonin said that he was not involved in the study
.
"The diameter of the NPC's central transport channel is larger than previously thought.
This fact suggests that the pores may have impressive structural flexibility
.
This may be important for the cells to adapt to growing transport demands
.
"

Next, Schuller and Schwartz hope to understand how the size of the pore affects which molecules can pass through
.
For example, scientists have only recently determined that this hole is large enough to allow intact viruses like HIV to enter the nucleus
.
The same principle applies to medical treatment: only drugs of appropriate size with specific properties can obtain cellular DNA
.

Schwartz particularly wanted to know whether all NPCs are the same, or whether their structure differs by species or cell type
.

He said: "We have been manipulating cells and extracting individual components from their native environment
.
Now we know that this method may have greater consequences than we thought
.
"

For more reference information, please see "The cellular environment shapes the nuclear pore complex architecture" by Anthony P.
Schuller, Matthias Wojtynek, David Mankus, Meltem Tatli, Rafael Kronenberg-Tenga, Saroj G.
Regmi, Phat V.
Dip, Abigail KR Lytton -Jean, Edward J.
Brignole, Mary Dasso, Karsten Weis, Ohad Medalia and Thomas U.
Schwartz, 13 October 2021, Nature .

DOI: 10.
1038/s41586-021-03985-3