Abstract:
:Regulation of the F-actin severing activity of gelsolin by Ca2+ has been investigated under physiologic ionic conditions. Tryptophan fluorescence intensity measurements indicate that gelsolin contains at least two Ca2+ binding sites with affinities of 2.5 x 10(7) M-1 and 1.5 x 10(5) M-1. At F-actin and gelsolin concentrations in the range of those found intracellularly, gelsolin is able to bind F-actin with half-maximum binding at 0.14 microM free Ca2+ concentration. Steady-state measurements of gelsolin-induced actin depolymerization suggest that half-maximum depolymerization occurs at approximately 0.4 microM free Ca2+ concentration. Dynamic light scattering measurements of the translational diffusion coefficient for actin filaments and nucleated polymerization assays for number concentration of actin filaments both indicate that severing of F-actin occurs slowly at micromolar free Ca2+ concentrations. The data suggest that binding of Ca2+ to the gelsolin-F-actin complex is the rate-limiting step for F-actin severing by gelsolin; this Ca2+ binding event is a committed step that results in a Ca2+ ion bound at a high-affinity, EGTA-resistant site. The very high affinity of gelsolin for the barbed end of an actin filament drives the binding reaction equilibrium toward completion under conditions where the reaction rate is slow.
journal_name
Biophys Jjournal_title
Biophysical journalauthors
Kinosian HJ,Newman J,Lincoln B,Selden LA,Gershman LC,Estes JEdoi
10.1016/S0006-3495(98)77751-3subject
Has Abstractpub_date
1998-12-01 00:00:00pages
3101-9issue
6eissn
0006-3495issn
1542-0086pii
S0006-3495(98)77751-3journal_volume
75pub_type
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