BLE 18-1 Actin Cross-L inking Proteins MW Domain Organization Locaton 10 kDa 33.00 Filopodia, lamellipodia. stress tibers EF-I 50.000 Pseudopodia 55.000 Filopodia. lamellipodia, stress fibers, microvilli. acrosomal process scral 102、000 Acrosomal process GROiP I 92,000 Intestinal and kidney brush border Microvilli Dematin 48,000 Ervthrocvte cortical nctwork GRoUP III (CH-domain superfamily Fimbrin 68,000 Microvilli, stereocilia. adhesion plaques, yeast attin cables 102、000 Filopodia, lamellipodia, stress tibers, adhesion plagues Spectrin C280,000 Cortical networks B:246、00 275000 istr 427,000 ETUTTITINTITTROTTY Muncle cortical net works ABP 120 92000 pseudopodia 280,000 ilopodia, pseudopodia, stress bers w Bar, thw won I hw tone has a imte clin bofin r dmri. Gmup i prmtr t'e
They can be divided into several categories based on their presumed function in the cell, which also depending upon the their concentration, the modified state of proteins (e. g phosphorylated or not) and the prevailing environment such 2+ as ca,p H TABLE18-2 Some Cytosolic Proteins That Control Actin Polymerization MW Activin cofilin 15,0 eCAP39 40).00 Capping((i)endl Severn 40.000 Severing, capping gelsolin 87,00 Severing, capping 1/+)endl villin 9200 Cross I nking, severing, capping 3600 Capping [+)end 32.000 Tropomodulin 40.000 Capping I()endl
They can be divided into several categories based on their presumed function in the cell, which also depending upon the their concentration, the modified state of proteins (e.g. phosphorylated or not) and the prevailing environment such as Ca2+, pH
1) Monomer-sequestering proteins They sequester actin, holding it in a form that is unable to polymerize(up to 40% of actin) and keeping the cellular G-actin pool. Changes of monomer-sequestering proteins can shift the monomer-polymer equilibrium in a certain region of a cell and determine whether polymerization or depolymerization is favored at the time Thymosin (e.g. TB4) is small proteins( 5KD) with high affinity to bind ATP-G-actin and is main actin requesting protein in cells Profilin(15KD) also binds ATP-G-actins in 1: I ratio Profilin can act as a less effective sequestering protein and buffer 20 percent of unpolymerized actin, but its main function probably is to promote actin to be polymerized There are the complementary roles of profilin and Thymosin in regulating polymerization of G-actin
1) Monomer-sequestering proteins They sequester actin, holding it in a form that is unable to polymerize (up to 40% of actin) and keeping the cellular G-actin pool. Changes of monomer-sequestering proteins can shift the monomer-polymer equilibrium in a certain region of a cell and determine whether polymerization or depolymerizaion is favored at the time. Thymosin (e.g. T4 ) is small proteins (~ 5KD) with high affinity to bind ATP-G-actin and is main actinsequesting protein in cells. Profilin (~15KD) also binds ATP-G-actins in 1:1 ratio. Profilin can act as a less effective sequestering protein and buffer 20 percent of unpolymerized actin, but its main function probably is to promote actin to be polymerized. There are the complementary roles of profilin and Thymosin in regulating polymerization of G-actin