Researchers tug at molecules with optical tweezers

The strength of actin binding protein interactions cross-linking a surface bound and bead tethered actin filament are probed using force from an optical trap. Filamin in green which forms networks of actin filaments shown as a confocal image on the right
Date:8 July 2008 Tags:

Researchers from the Massachusetts Institute of Technology (MIT) have developed a novel technique to measure the strength of the bonds between two protein molecules important in cell machinery: gently tugging them apart with light beams.

It’s really giving us a molecular-level picture of what’s going on, said Matthew Lang, an assistant professor of biological and mechanical engineering and senior author of a paper on the work appearing in the 30 June advanced online issue of the Proceedings of the National Academy of Science.

Last year, Lang and others demonstrated that light beams could be used to pick up and move individual cells around the surface of a microchip.

Now they have applied the optical tweezers to measuring protein micro-architectures, allowing them to study the forces that give cells their structure and the ability to move.

The researchers focused on proteins that bind to actin filaments, an important component of the cytoskeleton. Depending on the arrangement and interaction of actin filaments, they can provide structural support, help the cell crawl across a surface or sustain a load (in muscle cells).

“We’re trying to understand how Nature engineered these molecular linkages to use in different ways,” said Lang.

Actin filaments are most commonly found either bonded or cross-linked by a much smaller actin binding protein.

The researchers studied the interactions between the proteins by pinning one actin filament to a surface and controlling the motion of the second one with a beam of light. As the researchers tug on a bead attached to the second filament, the bond mediated by the actin-binding protein eventually breaks.

With this technique, the researchers can get a precise measurement of the force holding the proteins together, which is on the order of piconewtons (10^-12 newtons).

The same technique could be used to investigate many of the other hundreds of protein interactions that occur in the cytoskeleton, said Lang.

This article was written by Anne Trafton and originally appeared on the Massachusetts Institute of Technology News Office website on 30 June 3008.