Department of Chemistry and Biochemistry

Faculty

ajith Ajith Karunarathne

Assistant Professor
Email: ajith.karunarathne@utoledo.edu
Office: BO 2098 A/B
Phone: (419) 530-7880
Fax: (419) 530-4033

Professional Background:
B.S.: University of Sri Jayewardenepura, Sri Lanka
PhD.: Michigan State University, East Lansing, Michigan, USA
Postdoctoral: Washington University School of Medicine, St. Louis, Missouri, USA 

Our Research Program

Publications

News: 

Our recent review article Titled " Subcellular optogenetics: controlling signaling and single cell behavior" is published in JOURNAL OF CELL SCIENCES. Click here to read the article.

Our recent findings are published in the journal NEURON on cross talks between Serotonin (5HT)- gastrin releasing peptide (GRP) receptors and subsequent effects on itch sensation. This new is on NBC news national coverage.

Click here watch NBC Brian Williams talking about this workNBC news

Click here to read this article

Exciting undergraduate and graduate research opportunities!

We offer a science outreach program for high school students to conduct research in life sciences!

Please contact Dr. Ajith Karunarathne for more information.

Research Interests:

Bioanalytical, Optical chemistry and Optogenetics, Molecular Imaging, and Signal Transduction
 
Research Synopsis:
Quantitative visualization of signaling in living cells surpasses cell disruptive approaches by providing spatio-temporal information about molecular entities that govern complex cellular processes. However there is a lack of approaches that govern signaling in a cell with precise spatial and temporal control to complement the existing assortment of live cell imaging methodologies.
 
To bridge the above gap, research in our group interfaces chemistry and biology with an emphasis on understanding signaling network dynamics in living cells. In order to do this we employ optical approaches not only to visualize but also to control and interrogate signaling in single cells. We currently dissect several pathologically important cell behaviors such as cell migration in cancer and neuronal damage repair. To facilitate this process, we generate tools of two kinds using a combination of chemical, genetic engineering, and molecular biology approaches. First, we design optical triggers to govern entire or individual components of signaling pathways in sub-cellular regions of single cells using specific wavelengths of light. Second, we develop efficient sensors to probe the dynamics of signaling molecules through fluorescence localization, bioluminescence or Förster resonance energy transfer (BRET or FRET) techniques.
 
Using optical tools, we interrogate cell behaviors by activating, inhibiting or modulating single, or multiple signaling modalities and simultaneously quantify the dynamics of the associated cellular and molecular responses. To perform these experiments, we employ single & multi-photon optogenetics and imaging approaches in combination with two and three dimensional microfluidic technologies and classical analytical instrumentation. Additionally, we make use of a multi photon confocal approach to perform intravital optogenetics and imaging to control and visualize single cell behaviors in-vivo. These approaches will help us identify and understand molecules, mechanisms and their dynamics in signaling networks that control cellular processes such as cancer metastasis, demyelination in the nervous system and modulation of itch sensation. Our approaches can be used to optically control a variety of cellular signaling and behavioral processes in a whole animal as therapeutic strategies. 
Optochemistry and G protein coupled opsin activation to control cellular signaling:
Cartoon
A.      11-cis-retinal has lambda-max around 380 nm. However, the lambda-max of the 11-cis retinal bound opsin varies from 350 nm (UV) to 640 nm (far red). During optical activation of opsin, a photon with appropriate energy interacts with the covalently bound chromophore 11-cis-retinal inducing its photo-isomerization to all-trans retinal. Conformational changes in opsin, due to this photo-isomerization, leads to opsin activation.
B.      GDP bound G protein a subunit has a higher affinity with the bg heterodimer. This interaction leads to the formation of abg heterotrimer. Opsin interacts with these heterotrimeric G proteins through its internal loops and the c-terminus at the cytosolic surface. Activated opsin facilitates exchange of GDP to GTP at the G protein a subunit resulting in heterotrimer dissociation and formation of active G protein subunits; aGTP and free bg. These activated G proteins are responsible for signaling effectors activation and subsequent signal transduction.
      There are limited number of heterotrimer G proteins controls majority of cellular signaling and physiological processes. Our group focuses on employing this G protein signaling conservation to achieve optical control of cellular and physiological processes through the recruitment native and engineered opsins. 
Optical control and visualization of subcellular signaling

 

Opsin induced G protein translocation

 

 


  

 

HeLa cell in the movie expresses G protein coupled vision receptors (Opsins) from the retina of the eye. Cell also expresses mCherry tagged gamma-9 subunit. On GPCR activation, G protein beta-gamma subunits translocate to the internal membranes. In this experiment, opsins in the left side of the cell are exposed to a confined blue light pulse (red box). Please note the disappearance of mCherry-gamma-9 from the exposed plasma membrane region immediately after the pulse and appearance in the adjacent ER. Opsin activation is transient and therefore, mCherry-gamma-9 returned to the plasma membrane towards the end of the movie. This shows that opsin can be used to spatially and temporally control signaling in subcellular regions in a cell(Subcelluar optogenetics). Plot shows the dynamics of mCherry-gamma9 in adjacent internal membranes.  Karunarathne et al, 2013, PNAS – E1565-E1574

Last Updated: 3/23/15