Title:
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Restoring structure and function in rhodopsin autosomal dominant
retinitis pigmentosa mutants
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Autosomal dominant retinitis pigmentosa is a genetic disorder that leads to
progressive vision loss and blindness. Over 150 AD RP mutations are located in
rhodopsin; a gene that encodes the dim light photoreceptor pigment of the rod cell.
Previous studies indicate that a large proportion of rhodopsin AD RP mutants fail to
fold correctly. Here, we have constructed all known ADRP mutations in the N- ,
terminus of rhodopsin in a synthetic bovine gene, and have also made other ADRP
mutations located at the transmembrane domain. We have examined their
expression and folding in HEK-293S cells and have attempted to restore the
misfolding phenotype by different approaches. We found that pharmacological
rescue with 11-cis retinal promotes folding in all AD RP mutants in the N-terminus,
but to different extents. However, the rescued purified pigments remain thermo-unstable and are defective in photobleaching and signal transduction.
j As an alternative approach, this set of mutants was put into rhodopsin mutant
N2C/D282C: a background which is more thermostable than WT rhodopsin due to
formation of a disulfide bond between the two introduced cysteines. We found that
some, but not all, AD RP mutants are repaired in this background and form a visible, pigment. In contrast to the 11 -cis retinal rescued pigments, the 2C-282C repaired
pigments have enhanced stability and have near normal photobleaching and signal
transduction properties. Our major conclusion from this work is that the N-terminal
cap of rhodopsin performs a key role in the folding and stabilization of rhodopsin as
well as in its signal transduction activity.
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