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S. Kolandaivelu, J. Hurley, V. Ramamurthy; AIPL1, a Protein Implicated in Childhood Blindness, Is Essential for the Assembly of Rod Phosphodiesterase (PDE) Subunits. Invest. Ophthalmol. Vis. Sci. 2007;48(13):2998.
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Mutations in Aipl1gene cause Lebers Congenital Amaurosis (LCA), a severe form of childhood blindness. Mice deficient in AIPL1 lack vision and exhibit severe retinal degeneration due to the absence of PDE subunits. However, the link between AIPL1 and stability of PDE subunits is not known. The purpose of this study is to understand the role of AIPL1 in synthesis of functional phosphodiesterase heterotrimers in rod photoreceptors.
We systemically dissected the role of AIPL1 on each of the steps of PDE maturation from prenylation to assembly of the PDE heterotrimers. The synthesis, stability and assembly of PDE subunits were probed by pulse-labelling, pulse-chase and immnuno-precipitation using ex-vivo retinal preparations from both wild-type and Aipl1 knockout mice.
In the absence of AIPL1, despite normal message levels of PDE subunits, majority of PDE subunits are absent. This result suggests that AIPL1 is involved in post-transcriptional control of PDE synthesis. Our pulse-label analysis clearly show that AIPL1 is not involved in the initial synthesis of PDE subunits. However, our pulse-chase analysis shows that AIPL1 plays an essential role in the stability of synthesized PDE subunits. In addition, our results show that this instability of PDE subunits is due to the lack of proper assembly of PDE subunits. We are currently evaluating the role of AIPL1 in folding and post-translational modification of PDE subunits
Our studies suggest that AIPL1 is involved in post-translational control of PDE synthesis. In the absence of AIPL1, PDEαßγ subunits do not assemble and is subsequently degraded by proteasomes. Based on our studies, we propose that AIPL1 is a specialized chaperone essential for the proper folding and/or assembly of functional PDE subunits.
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