Formins (formin homology proteins) are a group of proteins that are involved in the polymerization of actin and associate with the fast-growing end (barbed end) of actin filaments.[2] Most formins are Rho-GTPase effector proteins. Formins regulate the actin and microtubule cytoskeleton
[3][4] and are involved in various cellular functions such as cell polarity, cytokinesis, cell migration and SRF transcriptional activity.[5] Formins are multidomain proteins that interact with diverse signallingmolecules and cytoskeletal proteins, although some formins have been assigned functions within the nucleus.
Formins have been found in all eukaryotes studied.[1] In humans, 15 different formin proteins are present that have been classified in 7 subgroups.[6] By contrast, yeasts contain only 2-3 formins.[7]
Structure and interactions
Formins are characterised by the presence of three formin homology (FH) domains (FH1, FH2 and FH3), although members of the formin family do not necessarily contain all three domains.[8][9] In addition, other domains are usually present, such as PDZ, DAD, WH2, or FHA domains.
The proline-rich FH1 domain mediates interactions with a variety of proteins, including the actin-binding proteinprofilin, SH3 (Src homology 3) domain proteins,[10] and WW domain proteins. The actin nucleation-promoting activity of S. cerevisiae formins has been localized to the FH2 domain.[4] The FH2 domain is required for the self-association of formin proteins through the ability of FH2 domains to directly bind each other, and may also act to inhibit actin polymerisation.[11][12] The FH3 domain is less well conserved and is required for directing formins to the correct intracellular location, such the mitotic spindle, or the projection tip during conjugation.[13][14] In addition, some formins can contain a GTPase-binding domain (GBD) required for binding to Rho small GTPases, and a C-terminalconserved DRF autoregulatory domain (Dia-autoregulatory domain) (DAD). The GBD domain is a bifunctional autoinhibitory domain that interacts with and is regulated by activated Rho family members. Mammalian Drf3 contains a CRIB-like motif within its GBD for binding to Cdc42, which is required for Cdc42 to activate and guide Drf3 towards the cell cortex where it remodels the actin skeleton.[15] The DRF autoregulatory domain binds the N-terminal GTPase-binding domain; this link is broken when GTP-bound Rho binds to the GBD and activates the protein. The addition of the DAD to mammaliancells induces actin filament formation, stabilises microtubules, and activates serum-response mediated transcription.[15] Another commonly found domain is an armadillo repeat region (ARR) located in the FH3 domain.
Formins also directly bind to microtubules via their FH2 domain. This interaction is important in promoting the capture and stabilization of a subset of microtubules oriented towards the leading edge of migrating cells. Formins also promote the capture of microtubules by the kinetochore during mitosis and for aligning microtubules along actin filaments.[18][19]
↑Evangelista M, Zigmond S, Boone C (July 2003). "Formins: signaling effectors for assembly and polarization of actin filaments". Journal of Cell Science. 116 (Pt 13): 2603–11. doi:10.1242/jcs.00611. PMID12775772.
↑Gunning PW, Ghoshdastider U, Whitaker S, Popp D, Robinson RC (June 2015). "The evolution of compositionally and functionally distinct actin filaments". Journal of Cell Science. 128 (11): 2009–19. doi:10.1242/jcs.165563. PMID25788699.
↑Kitayama C, Uyeda TQ (February 2003). "ForC, a novel type of formin family protein lacking an FH1 domain, is involved in multicellular development in Dictyostelium discoideum". Journal of Cell Science. 116 (Pt 4): 711–23. doi:10.1242/jcs.00265. PMID12538772.
↑Wallar BJ, Alberts AS (August 2003). "The formins: active scaffolds that remodel the cytoskeleton". Trends in Cell Biology. 13 (8): 435–46. doi:10.1016/S0962-8924(03)00153-3. PMID12888296.
↑Uetz P, Fumagalli S, James D, Zeller R (December 1996). "Molecular interaction between limb deformity proteins (formins) and Src family kinases". The Journal of Biological Chemistry. 271 (52): 33525–30. doi:10.1074/jbc.271.52.33525. PMID8969217.
↑Takeya R, Sumimoto H (November 2003). "Fhos, a mammalian formin, directly binds to F-actin via a region N-terminal to the FH1 domain and forms a homotypic complex via the FH2 domain to promote actin fiber formation". Journal of Cell Science. 116 (Pt 22): 4567–75. doi:10.1242/jcs.00769. PMID14576350.
↑Shimada A, Nyitrai M, Vetter IR, Kühlmann D, Bugyi B, Narumiya S, Geeves MA, Wittinghofer A (February 2004). "The core FH2 domain of diaphanous-related formins is an elongated actin binding protein that inhibits polymerization". Molecular Cell. 13 (4): 511–22. doi:10.1016/S1097-2765(04)00059-0. PMID14992721.
↑Kato T, Watanabe N, Morishima Y, Fujita A, Ishizaki T, Narumiya S (February 2001). "Localization of a mammalian homolog of diaphanous, mDia1, to the mitotic spindle in HeLa cells". Journal of Cell Science. 114 (Pt 4): 775–84. PMID11171383.
↑ 15.015.1Peng J, Wallar BJ, Flanders A, Swiatek PJ, Alberts AS (April 2003). "Disruption of the Diaphanous-related formin Drf1 gene encoding mDia1 reveals a role for Drf3 as an effector for Cdc42". Current Biology. 13 (7): 534–45. doi:10.1016/S0960-9822(03)00170-2. PMID12676083.
↑Xu Y, Moseley JB, Sagot I, Poy F, Pellman D, Goode BL, Eck MJ (March 2004). "Crystal structures of a Formin Homology-2 domain reveal a tethered dimer architecture". Cell. 116 (5): 711–23. doi:10.1016/S0092-8674(04)00210-7. PMID15006353.
