An S-Opsin Knock-In Mouse (F81Y) Reveals a Role for the Native Ligand 11-cis-Retinal in Cone Opsin Biosynthesis

Abstract

In absence of their natural ligand, 11-cis-retinal, cone opsin G-protein-coupled receptors fail to traffic normally, a condition associated with photoreceptor degeneration and blindness. We created a mouse with a point mutation (F81Y) in cone S-opsin. As expected, cones with this knock-in mutation respond to light with maximal sensitivity red-shifted from 360 to 420 nm, consistent with an altered interaction between the apoprotein and ligand, 11-cis-retinal. However, cones expressing F81Y S-opsin showed an ϳ3-fold reduced absolute sensitivity that was associated with a corresponding reduction in S-opsin protein expression. The reduced S-opsin expression did not arise from decreased S-opsin mRNA or cone degeneration, but rather from enhanced endoplasmic reticulum (ER)-associated degradation of the nascent protein. Exogenously increased 11-cis-retinal restored F81Y S-opsin protein expression to normal levels, suggesting that ligand binding in the ER facilitates proper folding. Immunohistochemistry and electron microscopy of normal retinas showed that Mueller cells, which synthesize a precursor of 11-cis-retinal, are closely adjoined to the cone ER, so they could deliver the ligand to the site of opsin synthesis. Together, these results suggest that the binding of 11-cis-retinal in the ER is important for normal folding during cone opsin biosynthesis.

Arrestin 1 and Cone Arrestin 4 Have Unique Roles in Visual Function in an All-Cone Mouse Retina

“…20 This is consistent with previous research, which showed that scotopic ERG amplitudes correspond with rhodopsin expression 69,70 and single-cell responses from cones correspond with the relative amounts of cone opsin expression. 71,72 In this study, no increased M-opsin immunoreactivity increase was noted in 2-month-old retinas with our immunoblot experiments (Fig. 4), and these data are consistent with our previous results in WT and Arr4 À/À mice.…”

The C. elegans Taste Receptor Homolog LITE-1 Is a Photoreceptor

“…“±” represents SEM. The numbers for cryptochromes and opsins were from published literature: cryptochrome (Thompson and Sancar, 2002), bacterial rhodopsin (Oesterhelt and Hess, 1973), rhodopsin (Okano et al, 1992), melanopsin (Matsuyama et al, 2012), UV opsin (Insinna et al, 2012), blue opsin (Vought et al, 1999), green opsin, and red opsin (Kolesnikov et al, 2014). …”

CRALBP supports the mammalian retinal visual cycle and cone vision

“…This results in mislocalization of cone opsin and very rapid degeneration of the cones (42,43), both of which are attributed to chromophore deficiency (42,44). Consistent with the role of chromophore in supporting cone opsin folding and expression, a recent study demonstrated that proper cone opsin expression requires sufficient chromophore supply to the endoplasmic reticulum (45). In addition, 11-cis retinal in the inner segment of cones also appears to facilitate the transport of several phototransduction proteins to the cone outer segments (46).…”