The retinitis pigmentosa GTPase regulator, RPGR, intellects with the delta subunit of rod cyclic GMP phosphodiesterase

Recently, the retinitis pigmentosa 3 (RP3) gene has been cloned and named retinitis pigmentosa GTPase regulator (RPGR). The amino-terminal half of RPGR is homologous to regulator of chromosome condensation (RCC1), the nucleotide exchange factor for the small GTP-binding protein Ran. In a yeast-two-hybrid screen me identified the delta subunit of rod cyclic GMP phosphodiesterase (PDE delta) as interacting with the RCC1-Iike domain (RLD) of RPGR (RpGR(392)). The interaction of RPGR with PDE delta was confirmed by pull-down assays and plasmon surface resonance. The binding affinity mas determined to be 90 nM. Six missense mutations at evolutionary conserved residues within the RLD, which were found in RP3 patients, were analyzed by using the two-hybrid system, All missense mutations showed reduced interaction with PDE delta, A non-RP3-associated missense substitution outside the RLD, V36F, did not abolish the interaction with PDE delta, PDE delta is widely expressed and highly conserved across evolution and is proposed to regulate the membrane insertion or solubilization of prenylated proteins, including the catalytic subunits of the PDE holoenzyme involved in phototransduction and small GTP-binding proteins of the Rab family. These results suggest that RPGR mutations give rise to retinal degeneration by dysregulation of intracellular processes that determine protein localization and protein transport.