Our Research

PHOTOTRANSDUCTION IN PHOTORECEPTOR CELLS

Phototransduction is a fundamental biological process that encompasses a set of biochemical reactions initiating vision. The site of these events is in the outer segment of photoreceptor cells in the retina. Rhodopsin, a member of the G protein-coupled receptor family, is the light receptor that initiates phototransduction and a major determinant in maintaining the structural integrity of photoreceptor cells. Rhodopsin dysfunction causes inherited retinal diseases such as retinitis pigmentosa, congenital night blindness, and Leber congenital amaurosis.

ORGANIZATION OF RHODOPSIN IN ROD OUTER SEGMENT DISC MEMBRANES

Rod photoreceptor cells are exquisitely sensitive and capable of generating a single photon response. To achieve this, cells must maximize the probability of photon capture and efficiency in signaling. The photon-sensing and initial signaling events in response to light occur in the rod outer segment. The high membrane concentration and supramolecular organization of rhodopsin in photoreceptor cells is thought to facilitate the exquisite sensitivity of photoreceptor cells and maintain photoreceptor cell health.

Little is known about how rhodopsin attains its observed supramolecular organization, how this organization is modulated, and how the photoreceptor cell maintains a steady-state organization. Our laboratory is characterizing the supramolecular organization of rhodopsin utilizing atomic force microscopy (AFM) and fluorescence resonance energy transfer (FRET).

Related Publications:

1. Senapati, S., Gragg, M., Samuels, I. S., Parmar, V. M., Maeda, A., and Park, P. S.-H. (2018) Effect of dietary docosahexaenoic acid on rhodopsin content and packing in photoreceptor cell membranes. Biochim. Biophys. Acta 1860, 1403-1413.

2. Rakshit, T., Senapati, S., Parmar, V., Sahu, B., Maeda, A., and Park, P. S.-H. (2017) Adaptations in rod outer segment disc membranes in response to environmental lighting conditions. Biophys. Acta – Molecular Cell Research 1864, 1691-1702

3. Mishra, A. K., Gragg, M., Stoneman, M., Biener, G., Oliver, J. A., Miszta, P., Filipek, S., Raicu, V., and Park, P. S.-H. (2016) Quaternary structures of opsin in live cells revealed by FRET spectrometry. Biochem. J. 473, 3819-3836

4. Rakshit, T., Senapati, S., Sinha, S., Whited, A. M., and Park, P. S.-H. (2015) Rhodopsin forms nanodomains in rod outer segment disc membranes of the cold blooded Xenopus laevis. PLoS One 10, e0141114

5. Rakshit, T. and Park, P. S.-H. (2015) Impact of reduced rhodopsin expression on the structure of rod outer segment disc membranes. Biochemistry 54, 2885-2894

6. Whited, A. M. and Park, P. S.-H. (2015) Nanodomain organization of rhodopsin in native human and murine rod outer segment disc membranes. Biochim. Biophys. Acta – Biomembranes 1848, 26-34

MUTANTS OF RHODOPSIN CAUSING RETINITIS PIGMENTOSA

Rhodopsin mutations are the largest cause of autosomal dominant retinitis pigmentosa, a progressive retinal degenerative disorder. Over 100 mutations have been identified in rhodopsin that cause retinal disease. Over half these mutations cause misfolding of the receptor molecule. Misfolded mutants form aggregates that are toxic to photoreceptor cells and cause cell death. The mechanism by which aggregates cause cell toxicity is still unclear. Our laboratory is studying the process of rhodopsin misfolding and the nature of misfolded mutant aggregates both in vitro and in vivo. 

Related Publications:

1. Vasudevan, S., Senapati, S., Pendergast, M., and Park, P. S.-H. (2024) Aggregation of rhodopsin mutants in mouse models of autosomal dominant retinitis pigmentosa. Nat. Commun. 15, 1451.

2. Vasudevan, S. and Park, P. S.-H. (2021) Differential aggregation properties of mutant human and bovine rhodopsin. Biochemistry 60, 6-18. 

3. Gragg, M. and Park, P. S.-H. (2018) Misfolded rhodopsin mutants display variable aggregation properties. Biochim. Biophys. Acta 1864, 2938-2948. 

4. Gragg, M., Kim, T. G., Howell, S., and Park, P. S.-H. (2016) Wild-type opsin does not aggregate with a misfolded opsin mutant. Biochim. Biophys. Acta - Biomembranes 1858, 1850-1859. 

5. Miller, L. M., Gragg, M., Kim, T. G., and Park, P. S.-H. (2015) Misfolded opsin mutants display elevated β-sheet structure. FEBS Lett. 589, 3119-3125.

CONSTITUTIVELY ACTIVE MUTANTS OF RHODOPSIN

The structure of rhodopsin is finely tuned for its function under scotopic conditions and facilitates the exquisite sensitivity of rod photoreceptor cells. While rhodopsin must be activated by light to initiate vision, constitutive activity (i.e., receptor activation in the absence of light stimulation) of the receptor can cause a range of inherited retinal diseases. Our laboratory is investigating the molecular mechanisms underlying retinal diseases caused by constitutively active rhodopsin.

Related Publications:

1. Senapati, S. and Park, P. S.-H. (2020) Differential adaptations in rod outer segment disc membranes in different models of congenital stationary night blindness. Biochim. Biophys. Acta 1862, 183396.

2. Colozo, A. T., Vasudevan, S., and Park, P. S.-H. (2020) Retinal degeneration in mice expressing the constitutively active G90D rhodopsin mutant. Hum. Mol. Genet. 29, 881-891.

3. Senapati, S., Poma, A. B., Cieplak, M., Filipek, S., and Park, P. S.-H. (2019) Differentiating between inactive and active states of rhodopsin by atomic force microscopy in native membranes. Anal. Chem. 91, 7226-7235.

4. Kawamura, S., Colozo, A. T., Ge, L., Müller, D. J., and Park, P. S.-H. (2012) Structural, energetic, and mechanical perturbations in a rhodopsin mutant that causes congenital stationary night blindness. J. Biol. Chem. 287, 21826-21835.