Single amino acid residue as a functional determinant of rod and cone visual pigments

Abstract

The visual transduction processes in rod and cone photoreceptor cells begin with photon absorption by the different types of visual pigments. Cone visual pigments exhibit faster regeneration from 11-cis-retinal and opsin and faster decay of physiologically active intermediate (meta II) than does the rod visual pigment, rhodopsin, as expected, due to the functional difference between rod and cone photoreceptor cells. To identify the amino acid residue(s) responsible for the difference in molecular properties between rod and cone visual pigments, we selected three amino acid positions (64, 122, and 150), where cone visual pigments have amino acid residues electrically different from those of rhodopsin, and prepared mutants of rhodopsin and chicken greensensitive cone visual pigment. The results showed that the replacement of Glu-122 of rhodopsin by the residue containing green-or red-sensitive cone pigment converted rhodopsin's rates of regeneration and meta II decay into those of the respective cone pigments, whereas the introduction of Glu-122 into green-sensitive cone visual pigment changed the rates of these processes into rates similar to those of rhodopsin. Furthermore, exchange of the residue at position 122 between rhodopsin and chicken green-sensitive cone pigment interchanges their efficiencies in activating retinal G protein transducin. Thus, the amino acid residue at position 122 is a functional determinant of rod and cone visual pigments.

Functional diversity of bitter taste receptor TAS2R16 in primates

“…For arbutin (electronic supplementary material, figure S1c), in which a hydroxyl group is added to the 4 0 position of phenyl-b-glucopyranoside, the responses of human and white-headed langur TAS2R16s showed similar EC 50 values (2.3 + 0.5 and 2.5 + 0.3, respectively), whereas I I II II II III III III IV IV IV V V VI VI VI VII VII VII The transmembrane topology is shown according to the structure of bovine rhodopsin. Grey circles and squares represent the putative binding site for salicin [12].…”

“…All sequences of PCR products were confirmed to be intact using standard BigDye Terminator chemistry (Applied Biosystems, CA, USA). Mutant vectors were constructed using QUIKCHANGE (Agilent Technology, CA, USA) as described previously [12].…”

Mechanisms of spectral tuning in the RH2 pigments of Tokay gecko and American chameleon

“…To date, only E122Q and M207L are known to cause significant λ max -shifts in RH2 pigments; that is, Q122E in the RH2 pigments of chicken (Imai et al, 1997), coelacanth (Yokoyama et al, 1999), and zebrafish (Chinen et al, 2005) increase the λ max by 13~16 nm, while L207M in coelacanth 2 (P478) increases the λ max by 6 nm (Yokoyama et al, 1999). Our new mutagenesis analyses also showed that Q122E in gecko 2 (P467) and chameleon 2 (P496) increased the λ max by ~15 nm (Table 1).…”

“…In fact, molecular analyses of spectral tuning in RH2 pigments are limited to those of chicken (Gallus gallus), coelacanth (Latemeria chalamnae), and zebrafish (Danio rerio) (Imai et al, 1997;Yokoyama et al, 1999;Chinen et al, 2005). Since they are reasonably distantly related to these species, reptiles provide an opportunity to explore the general molecular mechanisms of spectral tuning in RH2 pigments.…”

G Protein-Coupled Receptor Rhodopsin: A Prospectus

“…The short nature of this helix results from the presence of the plug, which edges up close to the chromophore. The plug also includes a disulfide bond formed by Cys 110 Helix VI, the second longest helix in rhodopsin, is composed of residues 244 to 276, 47 Å in length, and only slightly tilted by ∼5° from the vector perpendicular to the plane of membranes. It is strongly bent by 30° by Pro 267 .…”