Salamander UV cone pigment: Sequence, expression, and spectral properties
The visual pigment from the ultraviolet (UV) cone photoreceptor of the tiger salamander has been cloned, expressed, and characterized. The cDNA contains a full-length open reading frame encoding 347 amino acids. The phylogenetic analysis indicates that the highest sequence homology is to the visual pigments in the S group. The UV opsin was tagged at the carboxy-terminus with the sequence for the 1D4 epitope. This fusion opsin was expressed in COS-1 cells, regenerated with 11-cis retinal (A1) and immuno-purified, yielding a pigment with an absorbance maximum ([lambda]max) of 356 nm which is blue shifted from the absorption of retinal itself. The transducin activation assay demonstrated that this pigment is able to activate rod transducin in a light-dependent manner. Regeneration with 11-cis 3,4-dehydroretinal (A2) yielded a pigment with a [lambda]max of 360 nm, only 4 nm red shifted from that of the A1 pigment, while bovine rhodopsin generated with A2 showed a 16-nm red shift from the corresponding A1 pigment. These results demonstrate that the trend for a shorter wavelength pigment to have a smaller shift of [lambda]max between the A1 and A2 pigments also fits UV pigments. We hypothesize that the small red shift with A2 could be due to a twist in the chromophore that essentially isolates the ring double bond(s) from conjugation with the rest of the polyene chain.(Received April 6 2000)
(Accepted January 19 2001)
Key Words: Absorbance; Amphibians; Cone; Opsin; Photoreceptor; Retina; Salamander; Ultraviolet; Visual pigment.
c1 Address correspondence and reprint requests to: Jian-xing Ma, Department of Ophthalmology, Medical University of South Carolina, 167 Ashley Avenue, Charleston, SC 29403, USA. E-mail: email@example.com