Role of the N- and C-terminal actin-binding domains of gelsolin in barbed filament end capping.
Gelsolin is a bivalent Ca(2+)-modulated actin-binding protein that severs, nucleates, and caps filaments. In order to gain a better understanding of the capping mechanism we have studied N- and C-terminal gelsolin fragments, 14NT and 41CT, each of which contains a single functional actin-binding site. The very tight binding measured between gelsolin and the barbed filament end requires gelsolin to greatly decrease the dissociation rate constant of the terminal actin from this end. A mechanism that could account for the observed decrease in dissociation is one in which gelsolin links two actin monomers so that they dissociate more slowly as a dimer. This cannot be the only mechanism, however, since, as shown here, 14NT and 41CT, fragments with single actin-binding sites, decrease the dissociation rate of the capped terminal actin molecule. The observations suggest that these fragments induce a conformational change in the actin monomer that either increases the affinity or alters the kinetics of the terminal actin-actin bond. The available data argue for strengthening of the terminal actin-actin bond.
Weber
A
A
Department of Biochemistry and Biophysics, University of Pennsylvania School of Medicine, Philadelphia 19104.
Pring
M
M
Lin
S L
SL
Bryan
J
J
D000177:Acrosome / Q000648:ultrastructure; D008841:Actin Cytoskeleton / Q000378:metabolism*; D000199:Actins / Q000737:chemistry / Q000378:metabolism*; D000818:Animals; D002118:Calcium / Q000378:metabolism; D002135:Calcium-Binding Proteins / Q000737:chemistry / Q000378:metabolism*; D004533:Egtazic Acid / Q000494:pharmacology; D018260:Gelsolin; D006737:Horseshoe Crabs; D066298:In Vitro Techniques; D007700:Kinetics; D008297:Male; D008840:Microfilament Proteins / Q000737:chemistry / Q000378:metabolism*; D010446:Peptide Fragments / Q000378:metabolism; D011108:Polymers; D011485:Protein Binding
D000199:Actins; D002135:Calcium-Binding Proteins; D018260:Gelsolin; D008840:Microfilament Proteins; D010446:Peptide Fragments; D011108:Polymers; D004533:Egtazic Acid; D002118:Calcium