Visual Neuroscience



Salamander UV cone pigment: Sequence, expression, and spectral properties


JIAN-XING  MA a1c1, MASAHIRO  KONO a2, LIN  XU a1, JOYDIP  DAS a1, JAMES C.  RYAN a1, E. STARR  HAZARD  III a1, DANIEL D.  OPRIAN a2 and ROSALIE K.  CROUCH a1
a1 Department of Ophthalmology, Medical University of South Carolina, Charleston
a2 Department of Biochemistry and the Volen Center for Complex Systems, Brandeis University, Waltham

Abstract

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.

Correspondence:
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: majx@musc.edu