Ca2+-binding proteins in the retina: Structure, function, and the etiology of human visual diseases

Abstract

The complex sensation of vision begins with the relatively simple photoisomerization of the visual pigment chromophore 11‐cis‐retinal to its all‐trans configuration. This event initiates a series of biochemical reactions that are collectively referred to as phototransduction, which ultimately lead to a change in the electrochemical signaling of the photoreceptor cell. To operate in a wide range of light intensities, however, the phototransduction pathway must allow for adjustments to background light. These take place through physiological adaptation processes that rely primarily on Ca²⁺ ions. While Ca²⁺ may modulate some activities directly, it is more often the case that Ca²⁺‐binding proteins mediate between transient changes in the concentration of Ca²⁺ and the adaptation processes that are associated with phototransduction. Recently, combined genetic, physiological, and biochemical analyses have yielded new insights about the properties and functions of many phototransduction‐specific components, including some novel Ca²⁺‐binding proteins. Understanding these Ca²⁺‐binding proteins will provide a more complete picture of visual transduction, including the mechanisms associated with adaptation, and of related degenerative diseases. BioEssays 22:337–350, 2000. © 2000 John Wiley & Sons, Inc.