Light Used to Control Protein Behavior Inside Living Cells

Researchers have been studying protein function for decades, but until now manipulating protein activity at a precise time and place within a cell has been impossible. Now scientists from University of North Carolina, Chapel Hill and Max Planck Institute for Medical Research are reporting in the latest Nature a genetic approach that allows the activation of given proteins using a tightly focused, non destructive light source.
Details from the article abstract:

Here we have developed a new approach to produce genetically encoded photoactivatable derivatives of Rac1, a key GTPase regulating actin cytoskeletal dynamics in metazoan cells. Rac1 mutants were fused to the photoreactive LOV (light oxygen voltage) domain from phototropin, sterically blocking Rac1 interactions until irradiation unwound a helix linking LOV to Rac1. Photoactivatable Rac1 (PA-Rac1) could be reversibly and repeatedly activated using 458- or 473-nm light to generate precisely localized cell protrusions and ruffling. Localized Rac activation or inactivation was sufficient to produce cell motility and control the direction of cell movement. Myosin was involved in Rac control of directionality but not in Rac-induced protrusion, whereas PAK was required for Rac-induced protrusion. PA-Rac1 was used to elucidate Rac regulation of RhoA in cell motility. Rac and Rho coordinate cytoskeletal behaviours with seconds and submicrometre precision. Their mutual regulation remains controversial, with data indicating that Rac inhibits and/or activates Rho. Rac was shown to inhibit RhoA in mouse embryonic fibroblasts, with inhibition modulated at protrusions and ruffles. A PA-Rac crystal structure and modelling revealed LOV-Rac interactions that will facilitate extension of this photoactivation approach to other proteins.

Press release: Breakthrough uses light to manipulate cell movement …
Image: Activation of Rac in the red circle (left) led to localized cell protrusion and translocation of the kinase PAK to the cell edge (right hand image, Pak in red).
Abstract in Nature: A genetically encoded photoactivatable Rac controls the motility of living cells