Functional analysis of rod monochromacy-associated missense mutations in the CNGA3 subunit of the cone photoreceptor cGMP-gated channel.
Thirty-nine missense mutations, which had been identified in rod monochromacy or related disorders, in the CNGA3 subunit of cone photoreceptor cGMP-gated channels were analyzed. HEK293 cells were transfected with cDNA of the human CNGA3 subunit harboring each of these mutations in an expression vector. Patch-clamp recordings demonstrated that 32 of the 39 mutants did not show cGMP-activated current, suggesting that these 32 mutations cause a loss of function of the channels. From the remaining 7 mutants that showed cGMP-activated current, two mutations in the cyclic nucleotide-binding domain, T565M or E593K, were further studied. The half-maximal activating concentration (K(1/2)) for cGMP in the homomeric CNGA3-T565M channels (160microM) was 17.8-fold higher than that of the homomeric wild-type CNGA3 channels (9.0microM). Conversely, the K(1/2) for cGMP in the homomeric CNGA3-E593K channels (3.0microM) was 3-fold lower than that of the homomeric wild-type CNGA3 channels. These results suggest that the T565M and E593K mutations alter the apparent affinity for cGMP of the channels to cause cone dysfunction, resulting in rod monochromacy.
Muraki-Oda
Sanae
S
Department of Ophthalmology, Shiga University of Medical Science, Seta, Otsu 520-2192, Japan.
Toyoda
Futoshi
F
Department of Physiology, Shiga University of Medical Science, Seta, Otsu 520-2192, Japan.
Okada
Akira
A
Department of Ophthalmology, Shiga University of Medical Science, Seta, Otsu 520-2192, Japan.
Tanabe
Shoko
S
Institute of Vision Research, 12-23 Sanbonmatsu-cho, Atsuta-ku, Nagoya 456-0032, Japan.
Yamade
Shinichi
S
Department of Ophthalmology, Shiga University of Medical Science, Seta, Otsu 520-2192, Japan.
Ueyama
Hisao
H
Department of Biochemistry and Molecular Biology, Shiga University of Medical Science, Seta, Otsu 520-2192, Japan. Electronic address: datt@belle.shiga-med.ac.jp.
Matsuura
Hiroshi
H
Department of Physiology, Shiga University of Medical Science, Seta, Otsu 520-2192, Japan.
Ohji
Masahito
M
Department of Ophthalmology, Shiga University of Medical Science, Seta, Otsu 520-2192, Japan.
D002460:Cell Line; D003001:Cloning, Molecular; D003117:Color Vision Defects; D006152:Cyclic GMP / Q000378:metabolism*; D054815:Cyclic Nucleotide-Gated Cation Channels; D019281:Dimerization; D004305:Dose-Response Relationship, Drug; D006801:Humans; D007473:Ion Channels / Q000737:chemistry / Q000502:physiology*; D007700:Kinetics; D009154:Mutation; D020125:Mutation, Missense; D018408:Patch-Clamp Techniques; D010786:Photoreceptor Cells / Q000378:metabolism*; D017949:Retinal Cone Photoreceptor Cells / Q000378:metabolism*; D017948:Retinal Rod Photoreceptor Cells / Q000378:metabolism*
C518238:CNGA3 protein, human; D054815:Cyclic Nucleotide-Gated Cation Channels; D007473:Ion Channels; D006152:Cyclic GMP