This piece was co-authored byDhwani Rupani, Dhruvika Chawalla, Malhar Khakharia, Vidhi Khanna
A team of researchers at the Tata Institute of Fundamental Research, Mumbai shed light on the collective forces produced by motor proteins driving intracellular transport in a recently published a paper in Cell. Rai et al describe how as a team, dyneins are able to carry a much higher load than a team of kinesins. This is despite the fact that a single dynein motor is able to carry a much smaller load than kinesin.
Kinesins and dyneins are motor proteins present in cells, and facilitate the transport of viruses and organelles such as mitochondria throughout the cytoplasm via microtubules. Transport processes involved in day to day functions of the cell require large forces which are likely driven by multiple motors, as single motors are unable to provide sufficient force. This transport is characterised by step – like motion of these motor proteins over microtubules. In a fascinating description, Roop Mallik whose team led the research says, “The cell may have its own ways in which motor proteins adapt to do the required amount of work. How these motors generate force as a team is what our research is all about.”
Roop Mallik’s team found that dyneins have the ability to change step size depending upon the load being carried, as opposed to which kinesins take fixed steps. In case of kinesins moving a load, they are unable to “fall back” and work as a team, i.e the leading kinesins do not slow down for the lagging kinesins, concentrating the load on a single kinesin, and ultimately leading to its detachment. On the other hand dyneins have the ability to change their step size according to the load, just like a self-regulating gear. This capacity allows dyneins to work as an integral part of a larger team, distributing the load and supporting each other.
Researchers introduced latex beads into cells to form latex bead phagosomes (LBPs) that became the motor proteins’ cargo inside cells. Movement of LBPs over microtubules was studied using a precisely calibrated optical trap. An optical trap is a device that makes use of converging laser beams to exert a restoring force on LBPs, which can be used to measure the displacement of LBPs by direct proportionality. A clear increase in the magnitude of force with increase in the dynein number was observed, supporting the hypothesis.
Roop Mallik’s Laboratory has further moved onto understanding the role of motor proteins in other cellular processes. They have begun experiments to test the role of motor proteins in the accumulation, fragmentation and change in size of fat droplets in cells. Studies of motor proteins also have implications in neurodegenerative diseases like Alzheimer’s disease and Lissencephaly where point mutations of the amino acid sequences in motor proteins are observed. We hope that this unusual subject is carried further, so in the future it could also be used as a target for therapy in cases of such fatal diseases.