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Measuring Spatially- and Directionally-varying Light Scattering from Biological Material
Published on: May 20, 2013
Spectral tuning of avian violet- and ultraviolet-sensitive visual pigments
S E Wilkie1, P R Robinson, T W Cronin
1Departments of Molecular Genetics and Visual Science, Institute of Ophthalmology, University College London, Bath Street, London, EC1V 9EL, U.K.
Biochemistry
|July 13, 2000
Summary
Avian visual pigments, crucial for bird vision, exhibit a wide range of light sensitivities. Researchers identified key amino acid changes, like Ser to Cys at site 90, that explain spectral shifts in bird vision.
Area of Science:
- * Molecular biology
- * Vision science
- * Biochemistry
Background:
- * Avian violet- and ultraviolet-sensitive visual pigments share similarities with mammalian violet-sensitive pigments.
- * Unlike mammals, bird pigments display a broad spectrum of maximum absorbance (lambda max) values, ranging from approximately 370 nm to 430 nm.
- * Previous research has characterized avian pigments with lambda max values around 420 nm (chicken) and in the UV range (budgerigar, canary).
Purpose of the Study:
- * To present the amino acid sequences of visual pigments from Humboldt penguin and pigeon, with intermediate lambda max values of 403 nm and 409 nm, respectively.
- * To identify specific amino acid sites responsible for the variation in lambda max values among different avian species.
- * To investigate the functional impact of identified amino acid substitutions on pigment spectral properties through in vitro expression.
Main Methods:
- * Isolation and sequencing of visual pigments from Humboldt penguin and pigeon.
- * Comparative analysis of amino acid sequences between penguin, pigeon, chicken, budgerigar, and canary pigments.
- * Site-directed mutagenesis of budgerigar cDNA to introduce specific amino acid substitutions, followed by in vitro expression in COS-7 cells and spectral analysis of regenerated pigments.
Main Results:
- * Five amino acid sites were identified as potentially correlating with differences in lambda max values across avian species.
- * In vitro expression revealed that three of these substitutions caused spectral shifts in the regenerated pigments.
- * A single amino acid replacement (Serine to Cysteine at site 90) in UV pigments resulted in a significant 35 nm short-wave shift, explaining the spectral difference between penguin (403 nm) and budgerigar/canary (~370 nm).
Conclusions:
- * Specific amino acid substitutions are key determinants of spectral tuning in avian visual pigments.
- * The Ser90Cys substitution is a major factor contributing to the shift from violet to UV sensitivity in certain bird species.
- * This study provides a molecular basis for understanding the evolution of diverse visual sensitivities in birds.
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