Pikachurin

Pikachurin, also known as AGRINL (AGRINL) and EGF-like, fibronectin type-III and laminin G-like domain-containing protein (EGFLAM), is a protein that in humans is encoded by the EGFLAM gene.^[5][6][7]

Pikachurin is a dystroglycan-interacting protein which has an essential role in the precise interactions between the photoreceptor ribbon synapse and the bipolar dendrites.^[6] The binding with dystroglycan (DG) depends on several factors (glycosylation of DG, presence of divalent cations, presence of other proteins).

A non-correct binding between pikachurin and DG is associated with

Pikachurin is an extracellular matrix-like retinal protein first discovered in 2008 in Japan by Shigeru Sato et al.^[6] and named after Pikachu, a species of the Pokémon franchise.^[9] The name of this protein was inspired by Pikachu's "lightning-fast moves".^[9]

Pikachurin was initially identified in a

Dystroglycan ligand with other proteins is essential. Glycosylation of dystroglycan is necessary for its ligand binding activity. Mutations in glycosyltransferase enzymes cause abnormal glycosylation of dystroglycan. This hypoglycosylation is associated with less binding with other proteins and causes some congenital muscular dystrophy. Pikachurin is the most recently identified dystroglycan ligand protein and is localized in the synaptic cleft in the photoreceptor ribbon synapse. The binding between dystroglycan and pikachurin requires divalent cations. Ca²⁺ produces strongest binding; Mn²⁺ produces only faint bindings and no binding with Mg²⁺ alone. Dystroglycan has different domains that allow multiple Ca²⁺ sites to form a stable pikachurin-dystroglycan connection. This shows that pikachurin can form oligomeric structures; and suggests the possibility of clustering effects can be important in modulating pikachurin-dystroglycan interactions. Another thing to be considered is that the presence of NaCl (0.5M) strongly inhibits interaction between DG and other ligand proteins but has a modest inhibitory effect with pikachurin-DG ligand. This shows that there are differences between the binding of pikachurin-DG binding and DG binding with other proteins. Pikachurin seems to have more domains to bind with DG than other proteins. For example, experiments in ligand competition shows that presence of pikachurin inhibits laminin-111 binding with DG, but high concentrations of laminin-111 do not inhibit pikachurin binding to DG.^[8]

Function

The protein is colocalized with both dystrophin and dystroglycan at the ribbon synapses.

Pikachurin, along with

Synapse formation is crucial for the mammalian CNS (central nervous system) to function correctly. Retinal photoreceptors finish at the axon terminal which forms a specialized structure, the ribbon synapse, which specifically connects photoreceptor synaptic terminals with bipolar and horizontal cell terminals in the outer plexiform layer (OPL) of the retina.^[6] It is clear that Pikachurin, an extracellular matrix–like retinal protein, is localized to the synaptic cleft in the photoreceptor ribbon synapse.

Since pikachurin seems to provide better visual acuity, Sato et al. of the Osaka Bioscience Institute believe that the protein could be used to develop a treatment for retinitis pigmentosa and other eye disorders.^[6][13]

See also

• Fibronectin type III domain
• Laminin G-like domain
• Sonic hedgehog, another protein named after a popular video game character
  .
• Zbtb7, an oncogene that was originally named "Pokemon".
• Aerodactylus, a genus of pre-historic pterosaurs named after Aerodactyl, a pterosaur in the Pokémon franchise.
• Articuno, Zapdos, and Moltres
  .
• Pheromosa
  .