Actin-binding protein involved in motile and morphological processes. Inhibits actin polymerization, likely by sequestering G-actin. By capping the barbed ends of filaments, it also regulates motility. Seems to play an important role in clathrin-mediated endocytosis and distribution of endocytic organelles (By similarity). Interacts with G-actin; ADP-actin form and capping protein (CP). May also be able to interact with TWF2 and phosphoinositides, PI(4,5)P2. When bound to PI(4,5)P2, it is down-regulated (By similarity). Interacts with ACTG1 (PubMed:28493397). Diffuse cytoplasmic localization with perinuclear and G-actin-rich cortical actin structures sublocalization. Also found at membrane ruffles and cell-cell contacts (By similarity). Expressed at high levels in the colon, testis, ovary, prostate and lung. Expressed at lower levels in the brain, bladder and heart. Not detected in liver. Phosphorylated on serine and threonine residues. Defects in TWF1 has been found in a patient with isolated coloboma, a defect of the eye characterized by the absence of ocular structures due to abnormal morphogenesis of the optic cup and stalk, and the fusion of the fetal fissure (optic fissure). Isolated colobomas may be associated with an abnormally small eye (microphthalmia) or small cornea. Belongs to the actin-binding proteins ADF family. Twinfilin subfamily. Was originally thought to have protein tyrosine kinase activity. Molecular embrace - Issue 73 of August 2006