Structural Study of AIPL1: Molecular Basis of its Function and its Role in Blinding Diseases

Abstract

Leber's congenital amaurosis (LCA) is a severe form of childhood blindness, and mutations in the putative chaperone AIPL1 have been linked to LCA [1]. It is known that AIPL1 interacts with phosphodiesterase 6 (PDE6), a protein involved in visual phototransduction, in both rod and cone cells [2]. Recently, small-angle X-ray scattering experiments combined with homology modeling revealed the sub-domain arrangements of AIPL1 [3]. However, the molecular mechanism of the interaction between AIPL1 and PDE6 remains poorly understood due to a lack of high-resolution structural data. The interaction of AIPL1 and PDE6 is believed to be mediated by a prenyl group that is introduced at the C-terminus of PDE6 as a post-translational modification. To test this hypothesis we have employed a combined experimental and computational approach. Molecular dynamics (MD) simulations were carried out on the AIPL1 homology model, identifying the principal components that lead to large-scale conformational fluctuations. Subsequent MD studies will be carried out to identify the differences between wild-type AIPL1 and mutants of AIPL1 in their interaction with a C-terminal prenylated fragment of PDE6. Fluorescence studies will also be carried out to characterize the difference in binding of labeled prenyl ligands with several variants: wild-type AIPL1, mutants of AIPL1, and a mouse version of Aipl1, which lacks the C-terminal domain found in human AIPL1. Our studies will provide a biophysical understanding of the processes underlying this binding. These results have the promise to provide valuable insight into the role of AIPL1 in normal vision, and in blinding diseases that affect humans. [1] Sohocki, Nat. Gen., 24:79 (2000); [2] Ramamurthy, PNAS, 100:12630 (2003) Kolandaivelu, JBC, 284:30853 (2009) Kolandaivelu, HMG, 23(4):1002 (2014); [3] Majumder, J. Biol. Chem, 288:21320 (2013).