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Binding of More Than One Retinoid to Visual Opsins

Authors :
James D. Looney
Charles K. Riley
Rosalie K. Crouch
Clint L. Makino
Tetsuji Okada
Source :
Biophysical Journal. 99:2366-2373
Publication Year :
2010
Publisher :
Elsevier BV, 2010.

Abstract

Visual opsins bind 11-cis retinal at an orthosteric site to form rhodopsins but increasing evidence suggests that at least some are capable of binding an additional retinoid(s) at a separate, allosteric site(s). Microspectrophotometric measurements on isolated, dark-adapted, salamander photoreceptors indicated that the truncated retinal analog, β-ionone, partitioned into the membranes of green-sensitive rods; however, in blue-sensitive rod outer segments, there was an enhanced uptake of four or more β-ionones per rhodopsin. X-ray crystallography revealed binding of one β-ionone to bovine green-sensitive rod rhodopsin. Cocrystallization only succeeded with extremely high concentrations of β-ionone and binding did not alter the structure of rhodopsin from the inactive state. Salamander green-sensitive rod rhodopsin is also expected to bind β-ionone at sufficiently high concentrations because the binding site is present on its surface. Therefore, both blue- and green-sensitive rod rhodopsins have at least one allosteric binding site for retinoid, but β-ionone binds to the latter type of rhodopsin with low affinity and low efficacy.

Details

ISSN :
00063495
Volume :
99
Database :
OpenAIRE
Journal :
Biophysical Journal
Accession number :
edsair.doi.dedup.....da5f8af56ccdf6596a03734b6801b25e
Full Text :
https://doi.org/10.1016/j.bpj.2010.08.003