Visual perception begins with the capture of light by the photoreceptor cells of the retina, rods and cones, which by an enzymatic amplification cascade convert it into an electrical signal which is transmitted to higher order neurons and brain.
The photoreceptor cells measure and transmit at all times the intensity of light at each point of the visual field. They do it with extraordinary sensitivity, while the ability to modulate the sensitivity according to the ambient light. This modulation capability is essential to manage in the natural world, in that ambient light is constantly changing.
The ability to modulate the response to light depending on the light background, light adaptation, lies in a calcium signal. The light, in addition to changing the membrane potential of photoreceptors produces a lowering of calcium into the cell. This decline in signal coordinates calcium enzymatic feedback regulation phototransduction cascade at several levels, which counteracts the amplification. This control signal is mediated by calcium-binding proteins (neuronal calcium sensor proteins NCS), among which are proteins activating guanylate cyclase or GCAPs, for its acronym in English.
The line of research led by Ana Mendez in Idibell has as one of its objectives to characterize the molecular basis of adaptation to light, the role of GCAP proteins in this process, and understand how genetic faults at this level lead to different forms of inherited blindness. Recent work by the group that is now published in PLoS Genetics, shows that when it fails the conformational transition of these sensor proteins of calcium in photoreceptors, GCAP2, of the form “Free Ca2 +” to form “bound Ca2 +” severe retinal degeneration that differs mechanistically from the retinal dystrophy associated with genetic faults in GCAP1 is triggered.
The study shows how in the case of GCAP2 protein in its free form calcium is not distributed to the sensory compartment, but accumulates in the inner segment of the cell after being phosphorylated and retained by binding to 14-3-3. It is this accumulation of the protein in the erroneous segment which leads to cell death. The study found a new physiological mechanism of controlling the distribution of the cell GCAP2 intimately linked to disease, in the sense that a serious deregulation of this mechanism leads to rapid retinal degeneration in murine models.