Overexpression of rhodopsin alters the structure and photoresponse of rod photoreceptors.
Rhodopsins are densely packed in rod outer-segment membranes to maximize photon absorption, but this arrangement interferes with transducin activation by restricting the mobility of both proteins. We attempted to explore this phenomenon in transgenic mice that overexpressed rhodopsin in their rods. Photon capture was improved, and, for a given number of photoisomerizations, bright-flash responses rose more gradually with a reduction in amplification--but not because rhodopsins were more tightly packed in the membrane. Instead, rods increased their outer-segment diameters, accommodating the extra rhodopsins without changing the rhodopsin packing density. Because the expression of other phototransduction proteins did not increase, transducin and its effector phosphodiesterase were distributed over a larger surface area. That feature, as well as an increase in cytosolic volume, was responsible for delaying the onset of the photoresponse and for attenuating its amplification.
Wen
Xiao-Hong
XH
Department of Ophthalmology, Massachusetts Eye and Ear Infirmary and Harvard Medical School, Boston, Massachusetts, USA. wenx@meei.harvard.edu
Shen
Lixin
L
Brush
Richard S
RS
Michaud
Norman
N
Al-Ubaidi
Muayyad R
MR
Gurevich
Vsevolod V
VV
Hamm
Heidi E
HE
Lem
Janis
J
Dibenedetto
Emmanuele
E
Anderson
Robert E
RE
Makino
Clint L
CL
D000042:Absorption; D000818:Animals; D002417:Cattle; D002462:Cell Membrane / Q000737:chemistry / Q000378:metabolism; D005227:Fatty Acids / Q000032:analysis; D015870:Gene Expression; D008027:Light; D051379:Mice; D008822:Mice, Transgenic; D017948:Retinal Rod Photoreceptor Cells / Q000737:chemistry* / Q000378:metabolism* / Q000528:radiation effects; D012243:Rhodopsin / Q000096:biosynthesis / Q000235:genetics* / Q000378:metabolism*; D017299:Rod Opsins / Q000235:genetics
D005227:Fatty Acids; D017299:Rod Opsins; D012243:Rhodopsin