TEAM WORK: Dynein motor proteins carrying phagosomes along microtubules are weak individually, but strong when working in teams. As a group, dyneins usually take large steps when hauling cargo (1), but as a focused laser beam pulls the cargo in the opposite direction and load increases, the leading proteins shorten their steps (2). This allows trailing dyneins to catch up, meaning the individual proteins bunch together to better share the strain (3). Against even higher loads, dyneins activate “catch bonds,” attaching themselves to microtubules to ensure they don’t get ripped off the track (4).PRECISION GRAPHICS
The paper
A.K. Rai et al., “Molecular adaptations allow dynein to generate large collective forces inside cells,” Cell, 152:172-82, 2013.
Inside every cell is a busy transit system, with motor proteins carrying cargo back and forth on a network of polymerized protein filaments. The motor proteins traveling along these intracellular highways are essential for almost every cellular process. But while much is known about how single motors generate force, how they operate in teams is not clear.
To find out, Roop Mallik of the Tata Institute of Fundamental Research in Mumbai, India, and colleagues used optical tweezers to measure forces exerted in vivo by dyneins and kinesins, two types of motor proteins. With a focused laser beam, they trapped the cargo being carried—in this case, ...
