Protein may hold clues to blinding diseases

Madison, WI-A newly discovered protein in the eye of the fruit fly may shed light on blinding diseases such as age-related macular degeneration and retinitis pigmentosa in humans.

The protein, which researchers at the University of Wisconsin (UW)–Madison and collaborators have named XPORT, serves as a chaperone for two proteins key to sensory activities in the eye. One protein, rhodopsin, is responsible for absorbing light, and the other, transient receptor potential protein (TRP), is a channel that plays a role in calcium influx into cells.

XPORT guides the two proteins from the place where they are made in the cell to the location where they do their jobs. The chaperoning process is prone to error, and a malfunction in any of the steps can have dire consequences in tissues.

“Accumulation of misfolded proteins often leads to severe pathology and cell death, producing blinding diseases and other neurodegenerative diseases,” said Nansi Jo Colley, PhD, professor, Department of Ophthalmology and Visual Sciences, Department of Genetics, and the Eye Research Institute of the UW School of Medicine and Public Health. “Molecular chaperones are one of the first lines of defense in these fundamental processes.”

Dr. Colley and her team discovered XPORT as a result of screening a collection of 900 fruit-fly mutants that undergo retinal degeneration. The XPORT mutant displayed retinal degeneration and defects in rhodopsin and TRP. They named the protein XPORT, for exit protein of rhodopsin and TRP.

Although XPORT is an eye-specific protein that is expressed in flies and other insects, Dr. Colley expects that a protein very similar to XPORT exists in humans.

“TRP channels play a vital role as biological sensors, regulating calcium entering cells involved in vision, taste, olfaction, hearing, and touch,” Dr. Colley said, adding that the channels are found in many organisms and tissues. “Defective TRP channels can cause night blindness in certain people.”

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