# Phosducin family
## Phosducin family

The phosducin family is a group of proteins primarily known for their role in regulating heterotrimeric G-protein signaling. These proteins are found in various tissues, with notable expression in the retina and nervous system. Phosducin proteins are involved in modulating signal transduction by interacting with the G-protein beta-gamma (Gβγ) complex, thereby influencing multiple physiological processes.

## Structure and classification

Phosducins are small, cytosolic proteins characterized by a conserved phosducin-like domain, which facilitates their interaction with G-proteins. The family is broadly classified into:
* Phosducin (PDC): Expressed predominantly in retinal photoreceptor cells, PDC regulates visual signal transduction.
* Phosducin-like proteins (PhLPs): A subset of phosducins, including PhLP1, PhLP2, and PhLP3, which have diverse roles beyond vision, such as protein folding and cellular signaling.

## Functional roles
### 1. G-Protein regulation

Phosducins interact with the Gβγ subunits of heterotrimeric G-proteins, acting as modulators of G-protein-coupled receptor signaling. This interaction affects downstream pathways, including vision, neurotransmission, and hormonal signaling.

### 2. Role in vision

In retinal photoreceptors, phosducin binds to the Gβγ complex, regulating phototransduction. Under bright light conditions, phosducin is phosphorylated, leading to the release of Gβγ and allowing the resensitization of photoreceptors.

### 3. Protein folding and chaperone function

Some PhLPs, such as PhLP2 and PhLP3, function as co-chaperones in the CCT/TRiC chaperonin complex, assisting in the proper folding of actin and tubulin.

### 4. Neurotransmission and hormonal regulation

Beyond the retina, phosducins are expressed in the brain and endocrine tissues, where they influence neurotransmitter release and hormone signaling.

## Phosphorylation and regulation

Phosducin activity is regulated by phosphorylation through protein kinases such as protein kinase A and protein kinase C. When phosphorylated, phosducin loses its ability to bind Gβγ, altering downstream signaling dynamics.

## Implications in disease and therapeutics

Dysregulation of phosducin proteins has been linked to several diseases, including:
* Retinal disorders: Mutations or alterations in phosducin expression contribute to photoreceptor degeneration.
* Neurological disorders: PhLP dysfunction is associated with neurodegenerative diseases due to its role in protein folding.
* Cardiovascular regulation: Phosducin influences blood pressure by modulating sympathetic nervous system activity

## Human proteins containing this domain

| Gene | Aliases | Protein |
| PDC | MEKA | phosducin |
| PDCL | PhLP1 | phosducin-like |
| PDCL2 | GCPHLP | phosducin-like 2 |
| PDCL3 | PhLP2A | phosducin-like 3 |
| TXNDC9 | PhLP3 | thioredoxin domain containing 9 |
* The article need two subjects to be added PDCL2 and PDCL3 as separate article.
* ↑ Willardson, Barry M.; Howlett, Alyson C. (December 2007). "Function of phosducin-like proteins in G protein signaling and chaperone-assisted protein folding". Cellular Signalling. 19 (12): 2417–2427. doi:10.1016/j.cellsig.2007.06.013. ISSN 0898-6568. PMC 2095786. PMID 17658730.
* ↑ Lukov, Georgi L; Hu, Ting; McLaughlin, Joseph N; Hamm, Heidi E; Willardson, Barry M (June 2005). "Phosducin-like protein acts as a molecular chaperone for G protein βγ dimer assembly". The EMBO Journal. 24 (11): 1965–1975. doi:10.1038/sj.emboj.7600673. ISSN 0261-4189. PMC 1142607. PMID 15889144.
* ↑ Ruiz-Gómez, A.; Humrich, J.; Murga, C.; Quitterer, U.; Lohse, M. J.; Mayor, F. (2000-09-22). "Phosphorylation of phosducin and phosducin-like protein by G protein-coupled receptor kinase 2". The Journal of Biological Chemistry. 275 (38): 29724–29730. doi:10.1074/jbc.M001864200. ISSN 0021-9258. PMID 10884381.
* ↑ Bauer, Petra H.; Müller, Stefan; Puzicha, Mechthild; Pippig, Susanne; Obermaier, Brigitte; Helmreich, Ernst J. M.; Lohse, Martin J. (July 1992). "Phosducin is a protein kinase A-regulated G-protein regulator". Nature. 358 (6381): 73–76. Bibcode:1992Natur.358...73B. doi:10.1038/358073a0. ISSN 1476-4687. PMID 1319556.