Evolutionary replacement of UV vision by violet vision in fish

Area of Science:

• Evolutionary biology
• Molecular genetics
• Vision science

Background:

• Vertebrates evolved from ancestors with ultraviolet (UV) vision, with subsequent evolutionary shifts to violet vision in many species.
• Short wavelength-sensitive (SWS1) pigments mediate UV (approx. 360 nm) and violet (390-440 nm) vision, but the mechanisms driving these spectral changes remain unclear.

Purpose of the Study:

• To investigate the molecular mechanisms behind the evolution of violet vision in fish.
• To identify and characterize the SWS1 pigment responsible for violet sensitivity in scabbardfish (Lepidopus fitchi).

Main Methods:

• Cloning of the scabbardfish SWS1 pigment.
• Site-directed mutagenesis to alter pigment properties.
• Quantum mechanical/molecular mechanical (QM/MM) computations to analyze pigment-protein interactions.

Main Results:

• The scabbardfish SWS1 pigment exhibits violet sensitivity with a lambda(max) of 423 nm.
• Mutagenesis and computational analyses identified the deletion of Phenylalanine at position 86 (Phe-86) as crucial for violet sensitivity.
• This deletion causes a shift from an unprotonated to a protonated Schiff base-linked 11-cis-retinal, altering light absorption.

Conclusions:

• The scabbardfish provides a model for violet-sensitive SWS1 pigments in fish, suggesting widespread occurrence of similar pigments.
• Understanding these violet and UV pigments offers insights into the molecular basis of visual adaptations and their genetic underpinnings.