InterPro domain: IPR005455

This entry represents the Profilin family, which are small eukaryotic proteins that have different functions. In plants, they are major allergens present in pollens [ 1 ].

The majority of the Profilin family members binds to monomeric actin (G-actin) in a 1:1 ratio thus preventing the polymerisation of actin into filaments (F-actin). They can also in certain circumstance promote actin polymerisation [ 2 ]. However, some Profilin family members, such as Profilin4 from mammals, does not binds to actin and may have functions distinct from regulating actin dynamics [ 3 ]. It plays a role in the assembly of branched actin filament networks, by activating WASP via binding to WASP's proline rich domain [ 4 ]. Profilin may link the cytoskeleton with major signalling pathways by interacting with components of the phosphatidylinositol cycle and Ras pathway [ 5 , 6 ].

This entry also includes Asgard archaea profilins (Thor profilin, Loki profilin-1 and Loki profilin-2), which bind to actin and regulate the structure of the cytoskeleton. This indicates that Asgard archaea have a functional eukaryotic-like actin machinery [ 7 ].

Some Profilins can also bind to polyphosphoinositides such as PIP2 [ 8 ]. Overall sequence similarity among profilin from organisms which belong to different phyla (ranging from fungi to mammals) is low, but the N-terminal region is relatively well conserved. The N-terminal region is thought to be involved in actin binding.

1. Profilin: a relevant aeroallergen? J. Allergy Clin. Immunol. 128, 416-8
2. Profilin: emerging concepts and lingering misconceptions. Trends Biochem. Sci. 31, 197-205
3. Testis-expressed profilins 3 and 4 show distinct functional characteristics and localize in the acroplaxome-manchette complex in spermatids. BMC Cell Biol. 10, 34
4. Actin dynamics: assembly and disassembly of actin networks. Curr. Biol. 10, R891-5
5. Profilin: at the crossroads of signal transduction and the actin cytoskeleton. Bioessays 16, 465-72
6. Profilin, a weak CAP for actin and RAS. Cell 66, 419-21
7. Genomes of Asgard archaea encode profilins that regulate actin. Nature 562, 439-443
8. Alternative splicing of the mouse profilin II gene generates functionally different profilin isoforms. J. Cell. Sci. 113 Pt 21, 3795-803