fascin-like domain, beta-trefoil fold, found in the fascin-like family
The fascin-like family includes actin-bundling/crosslinking proteins facsin1-4, singed, hisactophilin, and FSHD region gene 1 protein (FRG1). Fascin, also called fascin-1, is an actin-binding protein that contains 2 major actin binding sites. It is involved in the organization of actin filament bundles and the formation of microspikes, membrane ruffles, and stress fibers. It plays an important role for the formation of a diverse set of cell protrusions, such as filopodia, and for cell motility and migration. It mediates reorganization of the actin cytoskeleton and axon growth cone collapse in response to nerve growth factor (NGF). Fascin-2, also called retinal fascin, is a photoreceptor-specific paralog of the actin-bundling protein fascin. It may play a pivotal role in photoreceptor cell-specific events, such as disk morphogenesis. Fascin-3, also called testis fascin, is a novel paralog of the actin-bundling protein fascin expressed specifically in the elongate spermatid head. Protein singed acts as an actin-bundling protein that may have a role in the asymmetric organization and/or movement of cytoplasmic components. It has a role in somatic cells during the formation of adult bristles and hairs, and in the female germline during oogenesis. Hisactophilin is a histidine-rich actin-binding protein from Dictyostelium discoideum. It exists in two isoforms, hisactophilin-1 (HatA, also called HS I) and hisactophilin-2 (HatB, also called HS II), which are both myristoylated and distributed between plasma membrane and cytoplasm. Hisactophilin may act as an intracellular pH sensor that links chemotactic signals to responses in the microfilament system of the cells by nucleating actin polymerization or stabilizing the filaments. Protein FRG1 binds to mRNA in a sequence-independent manner. It may play a role in regulation of pre-mRNA splicing or in the assembly of rRNA into ribosomal subunits. It may be involved in mRNA transport, as well as in epigenetic regulation of muscle differentiation through regulation of activity of the histone-lysine N-methyltransferase KMT5B. This family also contains many homologs from bacteria, such as Zobellia galactanivorans beta-porphyranase A (PorA). PorA (EC 3.2.1.178) cleaves the sulfated polysaccharide porphyran at the (1->4) linkages between beta-D-galactopyranose and alpha-L-galactopyranose-6-sulfate, forming mostly the disaccharide alpha-L-galactopyranose-6-sulfate-(1->3)-beta-D-galactose. It is inactive on the non-sulfated agarose portion of the porphyran backbone and displays a strict requirement for C6-sulfate in the -2 and +1-binding subsites. Members of this family contain a fascin-like domain with a beta-trefoil fold, which is characterized by 12 beta strands folded into three similar trefoil subdomains (alpha, beta, and gamma) associated to give an overall structure with pseudo-3-fold symmetry. The fascin subfamily contains four copies of the fascin-like domain.
Jiyao W et al.(2023). "The conserved domain database in 2023.",