A key barrier limiting progress in neuroscience has been the lack of technology capable of controlling individual neurons in the functioning brain.  It wasn't until 2005 that this problem was partially sovled by Karl Deisseroth and Ed Boyden at Stanford University who demonstrated a promising new apporach, referred to as optogenetics,  for  controlling nerves with light by expressing various  type-1  rhodopsins, normally found in  bacteria and algae, inside functioning neurons. 

Specific areas where this approach can have an impact include:  i) deciphering the funtion of the 200 billion neurons that make up the complex human brain wiring ; ii) restoring vision to the millions of persons in the U.S. suffering from macular degeneration and retinitis pigmentosa;  iii) characterizing and ultimately correcting defective neuronal activity in a host of neurodegenerative disorders including traumatic brain injury,  epilepsy, Parkinson's disease and Alzheimer's disease.

In this research project, we have developed new biophysical methods based on vibrational spectroscopy to characerize and understand the molecular mechanisms of  type-1 rhodopsins used in optogenetics.  One approach based on FTIR-difference spectroscopy allows small  changes in a protein to be detected and characterized at the level of individual  amino acid groups.  The method is so sensitive that even  small changes in the interaction of individual water molecules trapped in the rhodopsins can be detected.  A second approach uses  a confocal microscope and near infrared light to measure the vibrations of the light-absorbing chromophore, retinal, inside rhodopsins  in living cells where the voltage across the cell membrane can be controlled.

These methods were applied to Archaerhodopsin-3 (AR3) found in  the salt-loving archaebacterium Halorubrium sodomense.   This protein functions as a light-activated protein pump and has been used recently to silence neurons so that their function in intact neural circuits can be studied.  Furhtermore, a  mutant of this protein  has been used as  a fluorescent sensor of transmembrane potential in cells.  Small changes in the conformation of the AR3 protein in response to light and voltage were detected using the methods developed in this project . Similar studies were also initiated on a newly discovered channelrhodopsin known as CaChR1 from Chlamydomas augustae which can activate neurons with orange light.   These studies are providing a basis to understand how optogenetic rhodopsins function  and  ultimately to engineer improved versions  that can be used in both basic neuroscience investiations and to the treat neurodegenerative disorders.

Last Modified: 03/27/2014
Modified by: Kenneth J Rothschild