Bengaluru scientists help find new type of molecular motor

[ad_1]

Anupam Singh, a researcher at NCBS, uses a tool as part of the study. | Photo credit: Anupam Singh/Special Agreement

An international team of researchers, including that from the National Center for Biological Sciences (NCBS), Bangalore, has reported a new type of molecular motor. The discovery, significant in its own right, also opens the door to previously unexpected cellular processes and potential applications in biology and medicine.

Their paper was published in Nature Physics on May 4.

What is a molecular motor?

Every cell in the body is a complex soup of electrochemical reactions that produce energy, but are not enough. Cells also need to move things, like pulling two organelles together, moving cargo to and away from the nucleus, and fueling the movement of subcellular molecules.

Many of these actions are driven by molecular motors, which use biochemical energy to do mechanical work.

Disruption or deregulation of these processes can lead to deleterious effects that can manifest as different diseases, said Saikat Chowdhury, a senior scientist at the CSIR-Centre for Cellular and Molecular Biology, Hyderabad, in an email. He was not involved in the new study.

In a 2016 paper, Australian and German researchers reported that when an enzyme called Rab5 binds to a long protein called EEA1, the protein loses its taut, rigid shape and becomes limp. This collapse brings two membranes within a cell closer together.

What did the new study find?

In the new study, the researchers reported that EEA1 reverts to its rigid form in another mechanism so that it can become limp again to bring membranes together, creating a new type of two-part molecular motor.

At the time of the 2016 paper’s publication, it was unclear whether EEA1 could revert to its rigid form, so that the entire process could repeat itself without the help of other proteins.

The researchers figured it had to revert to its stiffer form because EEA1 works across thousands of membranes, and making a molecule the size of the protein for each pair of membranes would be wasteful.

At more than 200 nm, EEA is more than 100 times longer than typical proteins.

A long-standing question in the field is how EEA1-like molecules return to their elongated conformation; the new study addresses this question for the first time, said Dr. Chowdhury.

The NCBS & co. The team reported that EEA1 draws energy from a reaction called GTP hydrolysis to stiffen again. GTP hydrolysis is mediated by enzymes called GTPases. Rab5 is one of them.

Because of the ubiquitous association of small GTPases with such long molecules in eukaryotic cells, we believe this will mark a new class of molecular machines that operate as motors in a unique way and with novel collective effects, study co-author Shashi Thutupalli said in an E-Mail.

Dr. Thutupalli is from the Simons Center for the Study of Living Machines, NCBS. His collaborators are with the Max Planck Institute of Molecular Cell Biology and Genetics and the Cluster of Excellence Physics of Life, TU Dresden (both in Germany).

Why is the discovery significant?

They reported several novelties in their findings. The motor does not produce a lever-like back-and-forth action, as most motors do, but it does allow a molecule to switch its flexibility between two states. Furthermore, most molecular motors get their energy from another molecule called ATP, while the Rab5-EEA1 motor uses GTP.

Most of the other engines we know walk: they go in one direction, Dr. Thutupalli said, while this engine collapses and extends again, in the same place.

EEA1 can have one of several trillion shapes when floppy, but can only have one shape (rod) when stiff. The flaccid state has more entropy and is therefore entropically favored, according to Dr. Thutupalli. Then, as it goes from stiff to floppy, it exerts an entropic force on the membranes it pulls.

No other engine uses this force.

What are the potential applications?

Finding out how a single molecule moves inside a cell is difficult, but Dr Thutupalli said two students, Anupam Singh and Joan Antoni Soler, have found a clever way. Instead of trying to study the whole protein, they attached a small, fluorescent molecule to one end of EEA1, like a fly atop the Qutub Minar.

Then they used fluorescence correlation spectroscopy to monitor how the fluorescent molecule moved as Rab5 and EEA1 interacted.

They combined these observations with a concept in mechanics that allows engineers to calculate an object’s stiffness by looking at just one end.

This study is not only relevant to understanding membrane fusion by EEA1, but also provides a general mechanism applicable to many of these proteins or mechanochemical assemblies, which harness the chemical energy of nucleotide hydrolysis for work mechanic in the airframe, said Dr. Chowdhury.

[ad_2]