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At least 19 recordsLinked to original sources
PubMed1985

Kinetic analysis of F-actin depolymerization in the presence of platelet gelsolin and gelsolin-actin complexes.

Platelet gelsolin (G), a 90,000-mol-wt protein, binds tightly to actin (A) and calcium at low ionic strength to form a 1:2:2 complex, GA2Ca2 (Bryan, J., and M. Kurth, 1984, J. Biol. Chem. 259:7480-7487). Chromatography of actin and gelsolin mixtures in EGTA-containing solutions isolates a stable binary complex, GA1Ca1 (Kurth, M., and J. Bryan, 1984, J. Biol. Chem. 259:7473-7479). The effects of platelet gelsolin and the binary gelsolin-actin complex on the depolymerization kinetics of rabbit skeletal muscle actin were studied by diluting pyrenyl F-actin into gelsolin or complex-containing buffers; a decrease in fluorescence represents disassembly of filaments. Dilution of F-actin to below the critical concentration required for filament assembly gave a biphasic depolymerization curve with both fast and slow components. Dilution into buffers containing gelsolin, as GCa2, increased the rate of depolymerization and gave a first order decay. The rate of decrease in fluorescence was found to be gelsolin concentration dependent. Electron microscopy of samples taken shortly after dilution into GCa2 showed a marked reduction in filament length consistent with filament severing and an increase in the number of ends. Conversely, occupancy of the EGTA-stable actin-binding site by an actin monomer eliminated the severing activity. Dilution of F-actin into the gelsolin-actin complex, either as GA1Ca1 or GA1Ca2, resulted in a decrease in the rate of depolymerization that was consistent with filament end capping. This result indicates that the EGTA-stable binding site is required and must be unoccupied for filament severing to occur. The effectiveness of gelsolin, GCa2, in causing filament depolymerization was dependent upon the ionic conditions: in KCI, actin filaments appeared to be more stable and less susceptible to gelsolin, whereas in Mg2+, actin filaments were more easily fragmented. Finally, a comparison of the number of kinetically active ends generated when filaments were diluted into gelsolin versus the number formed when gelsolin can function as a nucleation site suggests that gelsolin may sever more than once. The data are consistent with a mechanism where gelsolin, with both actin-binding sites unoccupied, can sever but not cap F-actin. Occupancy of the EGTA-stable binding site yields a gelsolin-actin complex that can no longer sever filaments, but can cap filament ends.

Actins↗
PubMed1985

Interactions of gelsolin and gelsolin-actin complexes with actin. Effects of calcium on actin nucleation, filament severing, and end blocking.

Gelsolin is a calcium binding protein that shortens actin filaments. This effect occurs in the presence but not in the absence of micromolar calcium ion concentrations and is partially reversed following removal of calcium ions. Once two actin molecules have bound to gelsolin in solutions containing Ca2+, one of the actins remains bound following chelation of calcium, so that the reversal of gelsolin's effect cannot be accounted for simply by its dissociation from the ends of the shortened filaments to allow for elongation. In this paper, the interactions with actin of the ethylene glycol bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid (EGTA) stable 1:1 gelsolin-actin complexes are compared with those of free gelsolin. The abilities of free or complexed gelsolin to sever actin filaments, nucleate filament assembly, bind to the fast growing (+) filament ends, and lower the filament size distribution in the presence of either Ca2+ or EGTA were examined. The results show that both free gelsolin and gelsolin-actin complexes are highly dependent on Ca2+ concentration when present in a molar ratio to actin less than 1:50. The gelsolin-actin complexes, however, differ from free gelsolin in that they have a higher affinity for (+) filament ends in EGTA and they cannot sever filaments in calcium. The limited reversal of actin-gelsolin binding following removal of calcium and the calcium sensitivity of nucleation by complexes suggest an alternative to reannealing of shortened filaments that involves redistribution of actin monomers and may account for the calcium-sensitive functional reversibility of the solation of actin by gelsolin.

Actin Cytoskeleton↗
PubMed1987

Polyphosphoinositide micelles and polyphosphoinositide-containing vesicles dissociate endogenous gelsolin-actin complexes and promote actin assembly from the fast-growing end of actin filaments blocked by gelsolin.

The Ca2+-activated actin-binding protein gelsolin regulates actin filament length by severing preformed filaments and by binding actin monomers, stabilizing nuclei for their assembly into filaments. Gelsolin binds to phosphatidylinositol 4,5-bisphosphate (PIP2), with consequent inhibition of its filament severing activity and dissociation of EGTA-resistant complexes made with rabbit macrophage or human plasma gelsolin and rabbit muscle actin. This study provides evidence for an interaction of gelsolin with phosphatidylinositol monophosphate (PIP) as well as PIP2 and further describes their effects on gelsolin's function. Both phosphoinositides completely dissociate EGTA-insensitive rabbit macrophage cytoplasmic gelsolin-actin complexes and inhibit gelsolin's severing activity. The magnitude of inhibition depends strongly on the physical state of the phosphoinositides, being maximal in preparations that contain small micelles of either purified PIP or PIP2. Aggregation of PIP or PIP2 micelles by divalent cations or insufficient sonication or their incorporation into vesicles containing other phospholipids decreases but does not eliminate the inhibitory properties of the polyphosphoinositides. The presence of gelsolin partly inhibits the divalent cation-induced aggregation of PIP2 micelles. PIP2 in combination with EGTA inactivates gelsolin molecules that block the fast-growing end of actin filaments, thereby accelerating actin polymerization. Regulation of gelsolin by the intracellular messengers Ca2+ and polyphosphoinositides allows for the formation of several different gelsolin-actin intermediates with distinct functional properties that may be involved in changes in the state of cytoplasmic actin following cell stimulation.

Actins↗
PubMed1986

ATP hydrolysis by the gelsolin-actin complex and at the pointed ends of gelsolin-capped filaments.

To obtain kinetic information about the pointed ends of actin filaments, experiments were carried out in the presence of gelsolin which blocks all events at the kinetically dominant barbed ends. The 1:2 gelsolin-actin complex retains 1 mol/mol of actin-bound ATP, but it neither hydrolyzes the ATP nor exchanges it with ATP free in solution at a significant rate. On the other hand, the actin filaments with their barbed ends capped with gelsolin hydrolyze ATP relatively rapidly at steady state, apparently as a result of the continued interaction of ATP-G-actin with the pointed ends of the filaments. ATP hydrolysis during spontaneous polymerization of actin in the presence of relatively high concentrations of gelsolin lags behind filament elongation so that filaments consisting of as much as 50% ATP-actin subunits are transiently formed. Probably for this reason, during polymerization the actin monomer concentration transiently reaches a concentration lower than the final steady-state critical concentration of the pointed end. At steady state, however, there is no evidence for an ATP cap at the pointed ends of gelsolin-capped filaments, which differs from the barbed ends which do have an ATP cap in the absence of gelsolin. As there is no reason presently to think that gelsolin has any effect on events at the pointed ends of filaments, the properties of the pointed ends deduced from these experiments with gelsolin-capped filaments are presumably equally applicable to the pointed ends of filaments in which the barbed ends are free.

Actin Cytoskeleton↗
PubMed1986

Interactions of plasma gelsolin with actin. Isolation and characterization of binary and ternary plasma-gelsolin-actin complexes.

We have studied the interactions between plasma gelsolin and actin: firstly the complex formation between both proteins, secondly the effects of gelsolin and its complexes on G-actin polymerization and F-actin fragmentation. Complex formation has been studied by high-performance gel permeation chromatography; plasma gelsolin alone elutes at an Mr of about 77000 and a Stokes radius of 3.7 nm; complex formation occurs in the presence of Ca2+: by chromatography in the presence of EGTA, a binary complex is obtained with an Mr of 134000 and a Stokes radius of 4.7 nm; and by chromatography in the presence of Ca2+, a ternary complex is obtained with an Mr of 173000 and a Stokes radius of 5.2 nm. The binary complex is EGTA-stable. In relation to this stability of the binary complex, the depolymerizing function of gelsolin is not reversed upon chelation of Ca2+. The effects of plasma gelsolin and its complexes on both G-actin polymerization and F-actin fragmentation, and their Ca2+ dependence have been examined by viscometry and electron microscopy. The main conclusions of these studies are the following: the fast processes are the formation of ternary complex, which acts as a heteronucleus for G-actin polymerization, and the severing function of gelsolin, these fast processes are Ca2+-dependent; the slow processes are related to the capping ability of gelsolin or its complexes and are Ca2+-independent.

Actins↗
PubMed1988

Depression of gelsolin levels and detection of gelsolin-actin complexes in plasma of patients with acute lung injury.

Actin is the major protein of muscle and nonmuscle cells and is one of the most abundant body proteins. Physiologic or pathologic cell death may therefore result in the liberation of large amounts of this fibrous protein into the extravascular space. The potential for long actin filaments to increase plasma viscosity and change the rheology of the microvasculature are potentially obviated by the presence of 2 recently recognized plasma actin-binding proteins, vitamin-D-binding protein, and plasma gelsolin. As part of our initial evaluation of this newly recognized physiologic system in humans, we measured levels of gelsolin in plasma samples from patients with extensive lung injury. Gelsolin levels were depressed in 25 of 25 patients with the adult respiratory distress syndrome (ARDS), a disease characterized by massive cellular injury, as determined by either of 2 functional assays for gelsolin. Mean total gelsolin concentration of 20 patients with ARDS was 89.2 +/- 33 micrograms/ml (normal levels, approximately 240 micrograms/ml; p less than 0.001) and the mean free gelsolin concentration 69.6 +/- 29 micrograms/ml (normal levels, approximately 240 micrograms/ml; p less than 0.001). Gelsolin concentrations of 6 patients with bacterial pneumonias were also depressed, but to a lesser degree (mean total level, 117 +/- 21 micrograms/ml). Direct demonstration of the presence of actin in these plasmas (but not in normal plasmas) was performed by precipitating actin directly with DNase-Sepharose beads, or indirectly with antigelsolin-Sepharose beads, as confirmed with immunoblotting. Actin was found in 18 of 19 patients using DNase beads and in 7 of 19 using antigelsolin beads.(ABSTRACT TRUNCATED AT 250 WORDS)

Actins↗
PubMed1989

Gelsolin-polyphosphoinositide interaction. Full expression of gelsolin-inhibiting function by polyphosphoinositides in vesicular form and inactivation by dilution, aggregation, or masking of the inositol head group.

Calcium activates, and the polyphosphoinositides phosphatidylinositol 4-monophosphate (PIP) and phosphatidylinositol 4,5-bisphosphate (PIP2) inhibit the mechanical severing of actin filaments by gelsolin. Previous work indicated that the physical state of the two phospholipids is important for their effects in this system. This study correlates tests of gelsolin's severing function with quasielastic light scattering measurements of the size of mixed lipid particles and shows that the previously demonstrated diminution of the maximal effect of PIP2 in micellar form by aggregation of the micelles or mixing with other phospholipids is not the result of an absolute requirement for small lipid particles, but rather the masking of critical sites by aggregation, by sequestration in multilamellar vesicles, or by dilution of the polyphosphoinositides below a critical concentration. Large unilamellar vesicles of PIP and, importantly, PIP2 at low molar ratios (less than 3%) in mixed lipid vesicles of composition similar to plasma membranes are as active as PIP2 micelles. Aggregation or masking of polyphosphoinositide head groups by neomycin or profilin, respectively, blocked inhibition of gelsolin. Experiments with bilayer-forming phospholipids or with Triton X-100 indicate that a critical number of PIP2 molecules may be required for incipient effects on a gelsolin molecule. The actin and polyphosphoinositide binding protein profilin competed with gelsolin for binding PIP2 with a stoichiometry also suggesting binding to multiple PIP2 molecules. The membrane constituents sphingosine and cholesterol blocked the effect of PIP2 on gelsolin when added alone, but did not affect PIP2 when incorporated into mixed lipid bilayers containing phosphatidylinositol. The results suggest that profilin, small changes in membrane lipid composition, and, especially, membrane PIP2 concentration could have large effects on the modulation of gelsolin function in vivo.

Animals↗
PubMed1991

Gelsolin-related amyloidosis. Identification of the amyloid protein in Finnish hereditary amyloidosis as a fragment of variant gelsolin.

The Finnish type of familial amyloidosis is a systemic disease characterized by progressive cranial neuropathy, corneal lattice dystrophy, and distal sensimotor neuropathy. Amyloid fibrils were isolated from the kidney and heart of a patient with Finnish amyloidosis. After solubilization, the amyloid proteins were fractionated by gel filtration and purified by reverse-phase HPLC. Complete amino acid sequence analyses show that the two amyloid components obtained are fragments of gelsolin, an actin-modulating protein occurring in plasma and the cytoskeleton. The larger component represents residues 173-243 and the minor component residues 173-225, respectively, of mature gelsolin. When compared with the predicted primary structure of human gelsolin a single amino acid substitution is present in amyloid: at position 15 of the amyloid proteins an asparagine is found instead of an aspartic acid residue at the corresponding position (187) in gelsolin. Antibodies to a dodecapeptide of the amyloidogenic region of gelsolin specifically stain the tissue amyloid deposits in Finnish hereditary amyloidosis. The results show that the amyloid subunit protein in Finnish hereditary amyloidosis represents a new type of amyloid that is derived from an actin filament-binding region of a variant gelsolin molecule by limited proteolysis.

Amino Acid Sequence↗
PubMed1990

Gel electrophoresis of native gelsolin and gelsolin-actin complexes.

BHK gelsolin migrated on non-denaturing 8-25% polyacrylamide gels with an apparent molecular mass of 80 kDa. In the absence of Ca2+ no complex formation occurred between BHK gelsolin and actin. In the presence of Ca2+ two complex species were found: a ternary complex, GA2, of apparent molecular mass of 210 kDa at gelsolin:actin ratio of 1:2, and a novel quaternary complex, GA3, of apparent molecular mass of 247 kDa when actin was in excess. Both cytoplasmic and plasma gelsolin species form GA3 with skeletal muscle actin. No complexes larger than GA3 were observed. The formation of GA3 involves the binding of a third actin to the gelsolin molecule at the site previously assumed to be masked, rather than to the actin molecules already present in GA2. In preference to GA3, GA2 was incorporated into actin filaments stabilized with phalloidin. On chelation of free Ca2+, both GA2 and GA3 dissociated to form the EGTA stable binary complex (GA) with an apparent molecular mass of 140 kDa and free actin.

Actins↗
PubMed1992

The amino-terminal fragment of gelsolin is cross-linked to Cys-374 of actin in the EGTA-resistant actin-gelsolin complex.

It has been shown that the EGTA-resistant actin, one of the two actin molecules associated to gelsolin, can be predominantly cross-linked to gelsolin by benzophenone-4-maleimide (BPM), a photoaffinity-labeling reagent, which was conjugated to Cys-374 of actin prior to cross-linking (Doi, Y., Banba, M. and Vertut-Doï, A. (1991) Biochemistry 30, 5769-5777). When a chymotryptic digest of gelsolin containing the amino-terminal 15-kDa fragment was mixed with BPM-actin (42 kDa) and irradiated for cross-linking, a band of 58 kDa appeared on SDS-PAGE which was shown to contain actin molecule by using fluorescently labeled actin. The amino-terminal sequence of the 58-kDa complex was identical to that of gelsolin, confirming that the amino-terminal segment (residues 1-133) of pig plasma gelsolin lies closely to Cys-374 of actin in the EGTA-resistant complex.

Actins↗
PubMed1991

Cysteine-374 of actin resides at the gelsolin contact site in the EGTA-resistant actin-gelsolin complex.

The interaction of pig plasma gelsolin (G) and actin (A) was examined by using photoreactive 4-maleimidobenzophenone-actin (BPM-actin) in which BPM was previously conjugated to Cys-374 of actin through the maleimide moiety. In the presence of micromolar [Ca2+], the major cross-linked product observed after irradiation of the mixture of gelsolin (82 kDa) and actin (42 kDa) had an apparent molecular mass of 130 kDa although gelsolin predominantly existed in the form of an A2G complex (170 kDa). No cross-linked product was detected in the absence of Ca2+. BPM-actin itself did not give any cross-linked product. By use of fluorescent-labeled gelsolin, the cross-linked 130 kDa was shown to be an AG complex. The cross-linked complex was also formed from the A2G complex after removal of Ca2+ by [ethylenebis-(oxyethylenenitrilo)]tetraacetic acid (EGTA) followed by irradiation, indicating that it was the EGTA-resistant AG complex that was cross-linked. The results show that Cys-374 at the C-terminal segment of actin in the EGTA-resistant AG complex is 9-10 A apart from gelsolin. Furthermore, it was shown that the EGTA-resistant actin molecule once incorporated in the A2G complex did not exchange with free actin in the presence of Ca2+. This was also supported by the effect of phosphatidylinositol 4,5-bisphosphate, which did not dissociate the EGTA-resistant actin molecule from the A2G complex in the presence of Ca2+, but did after removal of Ca2+.

Actins↗
PubMed1987

pH-dependent rate of formation of the gelsolin-actin complex from gelsolin and monomeric actin.

The assembly of gelsolin with actin was followed by the increase of the fluorescence intensity of a fluorescence label bound to actin. The time course of the formation of the gelsolin-actin complex in the presence of micromolar [Ca2+] could be quantitatively interpreted by a model in which one actin molecule binds slowly to gelsolin in a rate-determining step and subsequently a second actin molecule is bound at least 40 times more rapidly. The rate of binding of the first actin molecule to gelsolin was found to be remarkably slow and to depend on the pH. The rate constants of formation of the gelsolin-actin complex range from 1.5 X 10(4) M-1 s-1 at pH 8 to 7 X 10(4) M-1 s-1 at pH 6.

Actins↗
PubMed1988

Nucleotide sequence of pig plasma gelsolin. Comparison of protein sequence with human gelsolin and other actin-severing proteins shows strong homologies and evidence for large internal repeats.

Pig plasma gelsolin (Mr = 81595; 739 residues) contains 704 identical residues out of a maximum 730 when compared to the cytoplasmic form of human gelsolin. The cDNA sequence also codes for a peptide of 33 residues N-terminal to the nine-residue plasma extension sequence previously reported: these 33 residues are highly homologous to the human signal peptide and plasma extension. Comparison of the gelsolin sequences with chicken brush border villin, severin from Dictyostelium discoideum and fragmin from Physarum polycephalum shows a strong evolutionary relationship between all these proteins. There are six large repeating segments in gelsolin and villin, and three similar segments in severin and fragmin. Although these multiple repeats cannot be related to any known function of these actin-severing proteins, this superfamily of proteins appears to have evolved from an ancestral sequence of 120 to 130 amino acid residues.

Animals↗
PubMed1986

Characterization of the Ca2+-induced conformational changes in gelsolin and identification of interaction regions between actin and gelsolin.

Serum gelsolin, a Ca2+-dependent protein regulating the length of actin filaments, undergoes conformational changes upon binding Ca2+. These were detected and analyzed by several approaches including ultraviolet difference spectroscopy, circular dichroism studies, analytical ultracentrifugation, thiol group titration, and limited proteolytic digestions. The effect of Ca2+ binding on the UV absorption difference spectrum and the near-UV circular dichroism spectrum was consistent with changes in the environments of tyrosine and phenylalanine residues. In the presence of Ca2+, the S0(20),w value decreased from 5.3 to 4.7. This latter result implies a transformation to a more asymmetric molecular shape. Gelsolin contained only two accessible thiol groups per mole of protein, one of which was titratable in the native protein; it was more accessible to 5,5'-dithiobis(2-nitrobenzoic acid) in the absence than in the presence of Ca2+. The limited digestion of gelsolin from serum and bovine aorta smooth muscle by two different proteases, chymotrypsin and trypsin, proceeded much faster in the presence of Ca2+ than in its absence with the production of three main fragments of about 40K, 32K, and 21K. This fragment mixture was found still able to shorten F-actin in a Ca2+-dependent manner; this severing activity was expressed by the isolated 40K peptide. Gelsolin was cross-linked to F- and G-actin by the zero-length cross-linker 1-ethyl-3-[3-(dimethylamino)propyl]-carbodiimide (EDC), generating a covalent 130K binary complex (actin1-gelsolin1) followed by a covalent 180K ternary complex (actin2-gelsolin1).(ABSTRACT TRUNCATED AT 250 WORDS)

Actins↗
PubMed1988

Circulating actin-gelsolin complexes following oleic acid-induced lung injury.

Plasma gelsolin is one of two extracellular proteins that bind actin, a major body protein, with high affinity. The authors performed a series of experiments to determine whether tissue injury leads to actin release and the formation of circulating actin-gelsolin complexes. Two functions of plasma gelsolin, filament-nucleating and filament-severing activity, were used to measure total and free gelsolin concentrations, respectively. Both gelsolin and gelsolin-actin complexes nucleate actin assembly, whereas only free gelsolin severs actin filaments. Therefore, nucleation reflects the total gelsolin concentration, severing, the free gelsolin concentration, and the difference, gelsolin-actin complexes. Injection of F-actin in the rat caused a reduction in the free, but not total, gelsolin levels, consistent with the formation of circulating actin-gelsolin complexes. Oleic acid (50 mg/kg) administered intravenously in rats, a treatment that causes acute hemorrhagic pulmonary necrosis, caused the free gelsolin concentration to fall to a greater extent than the total gelsolin concentration, which indicated the presence of circulating actin-gelsolin complexes. Lower doses (9-27 mg/kg) in rabbits caused a qualitatively similar but smaller change in the free gelsolin level. Plasma gelsolin was immunoprecipitated at times when actin-gelsolin complexes were present, as determined functionally, and bound actin was demonstrated by immunoblotting with an anti-actin antiserum. These studies show that considerable amounts of actin are released into the extracellular space during acute lung injury and that circulating actin-gelsolin complexes can be detected in the peripheral blood.

Actins↗
PubMed1988

Decreased plasma gelsolin levels in patients with Plasmodium falciparum malaria: a consequence of hemolysis?

Mammalian plasma contains a high-affinity actin-binding protein, plasma gelsolin, that severs actin filaments. Destruction of erythrocytes could result in the release of erythrocyte cytoskeletal actin into the plasma where it could bind to gelsolin. If the clearance of actin-gelsolin complexes exceeds its synthesis, lowering of the plasma gelsolin concentration might follow. To test this hypothesis, we measured plasma gelsolin levels in patients with falciparum malaria, a disease where at least part of the hemolysis takes place in the intravascular space and that is usually not accompanied by dysfunction of other organs. Two functional gelsolin assays showed that the mean plasma gelsolin concentration of 18 Nigerian children with Plasmodium falciparum malaria was less than 50% (P less than .001) of healthy Nigerian control subjects tested at the same time. Patients with pneumonia and febrile seizures also had depressed gelsolin levels, which indicates that factors other than hemolysis can lower gelsolin concentrations. Gelsolin levels were measured in 11 patients from The Gambia with P falciparum malaria before and approximately 3 weeks after treatment. In all cases the gelsolin level increased after treatment. To confirm the hypothesis that hemolysis can result in a lowering of plasma gelsolin levels, hemolysis was induced in rabbits, either acutely (by the injection of human serum) or subacutely (by the administration of phenylhydrazine). A fall in plasma gelsolin levels was seen, the rate of fall differing with the extent of hemolysis. Affinity adsorption of plasma from animals undergoing acute hemolysis with Sepharose beads coupled to the actin-binding protein DNase I, followed by immunoblotting of adherent proteins with antiactin antiserum demonstrated the presence of actin in circulating rabbit plasma. These studies suggest that under some conditions components of the red cell cytoskeleton are exposed to plasma proteins and that accelerated clearance of actin-gelsolin complexes may explain in part the depressed plasma gelsolin levels seen in patients with falciparum malaria.

Actins↗
PubMed1987

Quantitative measurement of plasma gelsolin and its incorporation into fibrin clots.

Gelsolin is a newly recognized actin-binding protein of plasma that severs actin filaments. The concentration of plasma gelsolin was measured by three independent methods: an enzyme-linked immunosorbent assay (ELISA) and two functional assays based on the ability of gelsolin to accelerate the polymerization of actin (a "nucleating" assay) or to sever preformed actin filaments (a "cutting" assay). The gelsolin level in 56 samples of human plasma ranged between 100 and 330 micrograms/ml. The mean plasma concentrations measured by the different assays were ELISA, 207 micrograms/ml; nucleating assay, 233 micrograms/ml; cutting assay, 247 micrograms/ml. The mean serum level of gelsolin was found to be 24% lower than that of plasma when paired samples were examined (183 micrograms/ml). The difference between plasma and serum gelsolin concentrations can be accounted for by a direct interaction between gelsolin and fibrin as shown by the binding of radiolabeled gelsolin to clots made from purified fibrinogen. Further, unlabeled gelsolin inhibits the binding of the labeled species to fibrin, but hemoglobin and albumin do not. Fibrin oligomers, but not fibrinogen, alter the sedimentation characteristics of radiolabeled gelsolin in sucrose gradients. The amount of gelsolin incorporated into the clot is increased if the clots are made in the presence of actin filaments or fibronectin. Thus, serum levels of gelsolin are lower than plasma levels because of an interaction between gelsolin and fibrin clots.

Actins↗