Faculty

CELLULAR PHOTOCHEMISTRY LABORATORY

Ajith Karunarathne, PhD
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

Research
Group Web Page and Twitter feed
Publications

NEWS

Our research named a Top 100 science paper of 2018

Our LATEST collaborative RESEARCH ARTICLE ON decoding calcium oscillations in neurons is just accepted at ACS Chemical Neuroscience. part of the work was performed @CHEMISTRYTOLEDO IN @UTOLEDO. CONGRATULATIONS TO AUTHORS!

Swain, S., Gupta, R. K., Ratnayake, K., Priyanka, P., Singh, R., Jana, S., Mitra, K., Karunarathne, A., Giri, L., (2018). Confocal imaging and k-means clustering of GABAB and mGluR mediated modulation of Ca2+ spiking in hippocampal neurons. ACS Chemical Neuroscience.

The latest research article on mechanisms of Blue light induced cellular toxicity from my research group at @ChemistryToledo in @UToledo. CONGRATULATIONS TO AUTHORS!

Ratnayake, K., Payton, J. L., Lakmal, O. H., and Karunarathne, A. (2018) Blue light excited retinal intercepts cellular signaling. Scientific Reports 8, 10207 https://www.nature.com/articles/s41598-018-28254-8

OUR RESEARCH SHEDS A NEW LIGHT ON GPCR REGULATION BY G PROTEINS. CONGRATULATIONS TO AUTHORS!

Samaradivakara, S., Kankanamge, D., Senarath, K., Ratnayake, K., and Karunarathne, A. (2018) G protein gamma (Ggamma ) subtype dependent targeting of GRK2 to M3 receptor by Gbetagamma. Biochemical Biophysical Research Communications, 2018 Jun 11. pii: S0006-291X(18)31295-6.

Two latest publications from our group just appeared online. Congratulations to authors!

Kankanamge, D., Ratnayake, K., Samaradivakara, S., and Karunarathne, A. (2018). Melanopsin (Opn4) employs Gαi and Gβγ as major signal transducers. Journal of Cell Science.

Senarath, K.; Kankanamge, D.; Samaradivakara, S.; Ratnayake, K.; Tennakoon, M.; Karunarathne, A. (2018). Regulation of G Protein βγ Signaling. International Review of Cell and Molecular Biology.

OUR RECENT JBC PAPER IS AMONG ONE OF THE MOST VIEWED ARTICLES. CONGRATULATIONS TO AUTHORS!

Senarath, K., Payton, J. L., Kankanamge, D., Siripurapu, P., Tennakoon, M., and Karunarathne, A. (2018) Gγ identity dictates efficacy of Gβγ signaling and macrophage migration. Journal of Biological Chemistry 2018; 293(8):2974-2989.

Year 2017 publications from our lab:

Siripurapu, P.; Kankanamge, D.; Ratnayake, K.; Senarath, K.; Karunarathne, A. J Biol Chem 2017, 292, 17482-17495.
Ratnayake, K.; Kankanamge, D.; Senarath, K.; Siripurapu, P.; Weis, N.; Tennakoon, M.; Payton, J. L.; Karunarathne, A. Methods in cell biology 2017, 142, 1-25.
Gupta, R. K.; Swain, S.; Kankanamge, D.; Priyanka, P. D.; Singh, R.; Mitra, K.; Karunarathne, A.; Giri, L. SLAS discovery 2017, 2472555217693378.

Our findings on itch sensation are now published in the journal SCIENCE SIGNALING. Click here to read it. Click here to read the UT news article on this research.

Our 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 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 work. NBC 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

1. GPCR and G protein signaling in immune and cancer cell migration.
2. Engineering optogenetic approaches to control subcellular signaling.
3. Engineering of biosensors and assay to quantify dynamic behaviors of signaling molecules.
4. Experiment-guided mathematical-computations modeling of cellular signaling networks.
5. Functional characterization opsin for their ability to control mammalian cell signaling.
6. Optical isomerization of push-pull molecules and the applicability in biomedical research.

Research Synopsis:

Quantitative visualization of signaling in living cells surpasses cell disruptive approaches by providing spatiotemporal 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 multiphoton 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:

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 alpha-betagamma heterotrimer. Opsin interacts with these heterotrimeric G proteins through its internal loops and the c-terminus at the cytosolic surface. Activated opsin facilitates the exchange of GDP to GTP at the G protein a subunit resulting in heterotrimer dissociation and formation of active G protein subunits; alphaGTP and free betagamma. These activated G proteins are responsible for signaling effectors activation and subsequent signal transduction.

There are a limited number of heterotrimer G proteins controls the 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

HeLa cell in the movie expresses G protein-coupled vision receptors (Opsins) from the retina of the eye. The 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(Subcellular optogenetics). The plot shows the dynamics of mCherry-gamma9 in adjacent internal membranes. Karunarathne et al, 2013, PNAS – E1565-E1574

Department of Chemistry and Biochemistry