Profilin

Short description: Actin-binding protein

Profilin

Profilin (blue) in complex with actin (green). (PDB code: 2BTF​)

Identifiers
Symbol| Profilin
Pfam| PF00235
InterPro| IPR002097
SMART| PROF
PROSITE| PS00414
SCOP2| 2btf / SCOPe / SUPFAM
CDD| cd00148
| Available protein structures:

Pfam | structures / ECOD
PDB| RCSB PDB; PDBe; PDBj
PDBsum| structure summary
PDB| 2btf​

Profilin is an actin-binding protein involved in the dynamic turnover and reconstruction of the actin cytoskeleton.[1] It is found in most eukaryotic organisms. Profilin is important for spatially and temporally controlled growth of actin microfilaments, which is an essential process in cellular locomotion and cell shape changes. This restructuring of the actin cytoskeleton is essential for processes such as organ development, wound healing, and the hunting down of infectious intruders by cells of the immune system.

Profilin also binds sequences rich in the amino acid proline in diverse proteins. While most profilin in the cell is bound to actin, profilins have over 50 different binding partners. Many of those are related to actin regulation, but profilin also seems to be involved in activities in the nucleus such as mRNA splicing.[2]

Profilin is the major allergen (via IgE) present in birch, grass, and other pollen.[citation needed]

## Contents

* 1 Sources and distribution
* 2 Regulation of actin dynamics
* 3 History of discovery
* 4 Allergen
* 5 Human genes
* 6 References
* 7 Further reading
* 8 External links

## Sources and distribution

Profilins are proteins of molecular weights of roughly 14–19 kDa. They are present as single genes in yeast, insects, and worms, and as multiple genes in many other organisms including plants. In mammalian cells, four profilin isoforms have been discovered; profilin-I is expressed in most tissues while profilin-II is predominant in brain and kidney.[3]

Asgard archaea use profilins.[4] Multiple eukaryotic diatom species lack profilins.[5]

Profilin is essential to host cell invasion by Toxoplasma gondii. Toxoplasma profilin is the specific pathogen-associated molecular pattern (PAMP) of TLRs 5, 11, and 12.[6]

## Regulation of actin dynamics

Profilin enhances actin growth in two ways:

* Profilin binds to monomeric actin thereby occupying an actin-actin contact site; in effect, profilin sequesters actin from the pool of polymerizable actin monomers. However, profilin also catalyzes the exchange of actin-bound ADP to ATP thereby converting poorly polymerizing ADP-actin monomers into readily polymerizing ATP-actin monomers. On top of that, profilin has a higher affinity for ATP- than for ADP-actin monomers. Thus in a mixture of actin, profilin, and nucleotides (ADP and ATP), actin will polymerize to a certain extent, which may be estimated by the law of mass action.[citation needed]
* Profilin-actin complexes are fed into growing actin polymers by proteins such as formin, Wiskott-Aldrich syndrome protein and Vasodilator-stimulated phosphoprotein which contain proline-rich FH1-domains. This mode of stimulated actin polymerization is much faster than unaided polymerization. Profilin is essential for this mode of polymerization because it recruits the actin monomers to the proline-rich proteins.[citation needed]

Profilin binds some variants of membrane phospholipids (phosphatidylinositol (4,5)-bisphosphate and inositol trisphosphate). The function of this interaction is the sequestration of profilin in an "inactive" form, from where it can be released by action of the enzyme phospholipase C.[citation needed]

Profilin negatively regulates PI(3,4)P2 limiting recruitment of lamellipodia to the leading edge of the cell.[7]

Profilin is one of the most abundant actin monomer binders, but proteins such as CAP and (in mammals) thymosin β4 have some functional overlaps with profilin. In contrast, ADF/cofilin has some properties that antagonize profilin action.

## History of discovery

Profilin was first described by Lars Carlsson in the lab of Uno Lindberg and co-workers in the early 1970s as the first actin monomer binding protein.[8] It followed the realization that not only muscle, but also non-muscle cells, contained high concentrations of actin, albeit in part in an unpolymerized form. Profilin was then believed to sequester actin monomers (keep them in a pro-filamentous form), and release them upon a signal to make them accessible for fast actin polymer growth.

## Allergen

Profilin allergy is significantly associated with respiratory allergy to grass pollen ( hay fever). After a person first becomes allergic to profilin through inhalation of grass or tree pollen, allergy to profilin-containing food and development of pollen-food syndrome occurs [9]: 3 How often pollen-allergic people across Europe become profilin allergic varies widely; As of 1997, from about 5% of Swedish birch pollen–allergic people to 51% in Spanish people allergic to Mercurialis annua were profilin allergic.[9] Profilin is the major allergen of certain food plants, for example, melon, orange, and soybean and thus allergy to melon, citrus fruits, tomato, and banana is a clinical marker of profilin hypersensitivity.[9] As of 2018 there was no "solid therapeutic approach" to treat profilin allergy.[9]

As of 2018, the list of members of the profilin family identified as allergens contained:[9]

* Actinidia deliciosa (kiwi fruit)
* Ambrosia artemisiifolia (short ragweed)
* Ananas comosus (pineapple)
* Apium graveolens (celery)
* Arachis hypogaea (peanut)
* Artemisia vulgaris (mugwort)
* Betula verrucosa (European white birch) and Betula pendula (silver birch)
* Capsicum annuum (bell pepper)
* Chenopodium album (pigweed)
* Citrus sinensis (sweet orange)
* Corylus avellana (hazel)
* Cucumis melo (muskmelon)
* Daucus carota (carrot)
* Glycine max (soybean)
* Helianthus annuus (sunflower)
* Hevea brasiliensis (para rubber tree [latex])
* Malus domestica (apple)
* Olea europaea (olive)
* Phleum pratense (timothy grass)
* Phoenix dactylifera (date palm)
* Prunus persica (peach)
* Pyrus communis (pear)
* Salsola kali (Russian thistle)
* Sinapis alba (yellow mustard)
* Solanum lycopersicum (tomato)

## Human genes

* PFN1, PFN2, PFN3, PFN4, PFN5

## References

1. ↑ "The evolution of compositionally and functionally distinct actin filaments". Journal of Cell Science 128 (11): 2009–19. June 2015. doi:10.1242/jcs.165563. PMID 25788699.
2. ↑ "Alternative splicing of the mouse profilin II gene generates functionally different profilin isoforms". Journal of Cell Science 113 (Pt 21): 3795–803. November 2000. doi:10.1242/jcs.113.21.3795. PMID 11034907. http://jcs.biologists.org/cgi/reprint/113/21/3795.pdf.
3. ↑ "In mouse brain profilin I and profilin II associate with regulators of the endocytic pathway and actin assembly". The EMBO Journal 17 (4): 967–76. February 1998. doi:10.1093/emboj/17.4.967. PMID 9463375.
4. ↑ "Genomes of Asgard archaea encode profilins that regulate actin". Nature 562 (7727): 439–443. October 2018. doi:10.1038/s41586-018-0548-6. PMID 30283132. Bibcode: 2018Natur.562..439A.
5. ↑ Aumeier, Charlotte; Polinski, Ellen; Menzel, Diedrik (October 2015). "Actin, actin-related proteins and profilin in diatoms: a comparative genomic analysis". Marine Genomics 23: 133–142. doi:10.1016/j.margen.2015.07.002. ISSN 1876-7478. PMID 26298820. https://pubmed.ncbi.nlm.nih.gov/26298820/.
6. ↑ "Toxoplasma gondii- derived profilin triggers human toll-like receptor 5-dependent cytokine production". Journal of Innate Immunity 6 (5): 685–94. August 2014. doi:10.1159/000362367. PMID 24861338.
7. ↑ "Profilin1 regulates PI(3,4)P2 and lamellipodin accumulation at the leading edge thus influencing motility of MDA-MB-231 cells". Proceedings of the National Academy of Sciences of the United States of America 107 (50): 21547–52. December 2010. doi:10.1073/pnas.1002309107. PMID 21115820. Bibcode: 2010PNAS..10721547B.
8. ↑ "Actin polymerizability is influenced by profilin, a low molecular weight protein in non-muscle cells". Journal of Molecular Biology 115 (3): 465–83. September 1977. doi:10.1016/0022-2836(77)90166-8. PMID 563468.
9. ↑ 9.0 9.1 9.2 9.3 9.4 Rodríguez del Río, P; Díaz-Perales, A; Sánchez-García, S; Escudero, C; Ibáñez, Md; Méndez-Brea, P; Barber, D (2018-02-19). "Profilin, a Change in the Paradigm". Journal of Investigational Allergology and Clinical Immunology 28 (1): 1–12. doi:10.18176/jiaci.0193. PMID 28760720. http://www.jiaci.org/summary/vol28-issue1-num1565.

## Further reading

"Profilin1 regulates PI(3,4)P2 and lamellipodin accumulation at the leading edge thus influencing motility of MDA-MB-231 cells". Proceedings of the National Academy of Sciences of the United States of America 107 (50): 21547–52. December 2010. doi:10.1073/pnas.1002309107. PMID 21115820. Bibcode: 2010PNAS..10721547B.

## External links

* Profilins at the US National Library of Medicine Medical Subject Headings (MeSH)

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