MIT researchers have used optical tweezers (light beams) to achieve a precise measurement of the strength of bonds between two protein molecules important in cell machinery.

They focused on proteins that bind to actin filaments, an important component of the cytoskeleton that provide structural support, help the cell crawl across a surface or sustain a load (in muscle cells).

They found the force holding the proteins together is on the order of piconewtons.

Also see:

Measuring molecular rupture forces between single actin filaments and actin-binding proteins